ALBERT

Beschreibung: 〈p〉Publication date: Available online 3 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Lamine Boumaiza, Ali Saeidi, Marco Quirion〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Among the methods used for evaluating the potential hydraulic erodibility of rock, the most common methods are those based on the correlation between the force of flowing water and the capacity of a rock to resist erosion, such as Annandale's and Pells' methods. The capacity of a rock to resist erosion is evaluated based on erodibility indices that are determined from specific geomechanical parameters of a rock mass. These indices include unconfined compressive strength (UCS) of rock, rock block size, joint shear strength, a block's shape and orientation relative to the direction of flow, joint openings, and the nature of the surface to be potentially eroded. However, it is difficult to determine the relevant geomechanical parameters for evaluating the hydraulic erodibility of rock. The assessment of eroded unlined spillways of dams has shown that the capacity of a rock to resist erosion is not accurately evaluated. Using more than 100 case studies, we develop a method to determine the relevant geomechanical parameters for evaluating the hydraulic erodibility of rock in unlined spillways. The UCS of rock is found not to be a relevant parameter for evaluating the hydraulic erodibility of rock. On the other hand, we find that the use of three-dimensional (3D) block volume measurements, instead of the block size factor used in Annandale's method, improves the rock block size estimation. Furthermore, the parameter representing the effect of a rock block's shape and orientation relative to the direction of flow, as considered in Pells' method, is more accurate than the parameter adopted by Annandale's method.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 9 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Qingrong Xiong, Diansen Yang, Weizhong Chen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this work, a multi-scale pore network with fractures is developed against experimental data in a wide range of degrees of water saturation. The pore network is constructed based on the measured microstructure information at several length scales. The gas transport is predicted by different gas transport equations (e.g. Javadpour, dusty gas model (DGM), Civan and Klinkenberg), which can consider the fundamental physics mechanisms in tight porous media, such as Knudsen diffusion and viscous flow. Then, the model is applied to simulating the gas permeability of the Callovo-Oxfordian (COx) claystone. The predicted gas permeability is basically in good agreement with the experimental data under different degrees of water saturation. Then the effects of micro-fissures are studied. The results suggest that this model can predict the gas flow in other tight porous media as well and can be applied to other fields such as carbon capture and storage.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 1 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Mateusz Janiszewski, Baotang Shen, Mikael Rinne〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉HYDROCK method aims to store thermal energy in the rock mass using hydraulically propagated fracture planes. The hydraulic fractures can interact with the pre-existing natural fractures resulting in a complex fracture network, which can influence the storage performance. This study investigates the interactions between hydraulic and natural fractures using a fracture mechanics approach. The new functionality of the fracture mechanics modelling code FRACOD that enables crossing of hydraulically driven fracture by a pre-existing fracture is presented. A series of two-dimensional numerical models is prepared to simulate the interaction at different approach angles in granitic rock of low permeability. It is demonstrated that multiple interaction mechanisms can be simulated using the fracture mechanics approach. The numerical results are in agreement with the modified Renshaw and Pollard analytical criterion for fracture crossing. The results show that for large approach angles, the hydraulic fracture crosses the natural fracture, whereas for small approach angles, the hydraulic fracture activates the natural fracture and the wing-shaped tensile fractures are propagated from its tips. Thus, the presence of fractures with low dip angles can lead to the growth of more complex fracture network that could impair the thermal performance of the HYDROCK method.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 1 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Arash Hosseini, S. Mohsen Haeri, Siavash Mahvelati, Aria Fathi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Loess as a subcategory of collapsible soils is a well-known aeolian deposit generally characterized as a highly-porous medium with relatively low natural density and water content and a high percentage of fine-grained particles. Such collapsible soil sustains large stresses under a dry condition with natural water content. However, it can experience high and relatively sudden decreases in its volume once it reaches a certain water content under a certain load and therefore, the natural condition of the soil might not be suitable for construction if the possibility of the exposure of the soil to excessive water exists during the lifetime of the project. This research presents the utilization of an innovative method for stabilization and improvement of Gorgan loessial soil. This method uses electrokinetics and nanomaterials to instigate additives to move through soil pores, as an in situ remedial measure. To assess the acceptability of this measure, the deformability and strength characteristics of the improved collapsible soil are measured and compared with those of the unimproved soil, implementing several unsaturated oedometer tests under constant vertical stress and varying matric suction. The result emphasizes the importance of the matric suction on the behavior of both improved and unimproved soils. The test results indicate that the resistance of the soil was highly dependent on the water content and matric suction of the soil. The oedometer tests on samples improved by 3% lime and 5% nanomaterials show considerable improvement of the collapse potential. Results also reveal that stabilized samples experience notably lower volume decrease under the same applied stresses.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 1 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Y.L. Gui, J.L. Shang, J.J. Ma, Z.Y. Zhao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Opening holes in rock including their size and distribution can affect the performance of rock-related structures. A good understanding on this will contribute to, for example, rock cavern design, and construction, tunnelling, and mining engineering. To improve the understanding, a comprehensive investigation of the opening hole effect on the rock mechanical behaviour under biaxial loading condition is carried out by virtue of a hybrid continuum-discrete element method. Laboratory specimens with both single hole and multi-hole of various radii are investigated and compared with the cases subjected to uniaxial compression. It is demonstrated that the confining pressure can increase both the stiffness and strength due to delaying the crack initiation and propagation. The increase due to the confining pressure is more evident for the compressive strength. For single hole specimens with 0.75 mm radius hole, the increase ratio of the compressive strength is a linear increasing function with width and the increase ratio ranges from 2.15 for the specimen with 3.5 mm width to 2.45 for 10 mm width. For the single hole specimen with 10 mm width, the increase ratio starts at 2.13 for the specimen with 0.75 mm radius hole, ascending to the peak of 2.37 for the specimen with 1 mm radius hole, followed by a decline to 2.2 for the specimen with 1.25 mm radius hole. However, for the multi-hole specimens, the increase ratio varies from 1.66 to 3.13. In addition, to verify the influence of confining pressure magnitude on the performance of the rock specimens, totalling 10 confining pressure levels are applied and modelled. The simulation results show that even though there are opening holes in the specimens, the simulated compressive strength generally follows the generalised Hoek-Brown model.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 8 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Sarada Prasad Pradhan, Tariq Siddique〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Large-scale slope destabilization could be aggravated due to swift urbanization and ever-rising demands of geoengineering projects such as dams, tunnels, bridges and widening roads. National Highway-58 connects Delhi to Badrinath in India, which passes through complex geomorphological and geological terrain and often encounters cut slopes susceptible to slope failures. In the present investigation, a detailed geotechnical appraisal is conducted along the road cut slopes from Rishikesh to Devprayag in the Himalayas. Twenty vulnerable road cut slopes were demarcated for detailed slope stability analysis using Phase2D finite element modeling simulator. Nonlinear generalized Hoek-Brown (GHB) criterion was adopted for stability analyses. Out of 20 slopes, five slopes (S6, S7, S18, S19 and S20) are unstable with factor of safety (FoS) less than or equals to 1, and thus needs immediate attention. The FoS of four slopes (S2, S9, S13 and S17) lie between 1 and 1.3, i.e. marginally stable and slopes S1, S3, S4, S5, S8, S10, S11, S12, S14, S15 and S16 are stable. Mohr-Coulomb (MC) criterion was also adopted to compare the slope stability analysis with GHB criterion. The FoS calculated from GHB criterion is close to that using MC criterion for lower values of FoS whereas for higher values, and the difference is marked. For the jointed rock in the Himalayan region, the nonlinear GHB criterion gives better results as compared to MC criterion and matches with the prevailing field conditions. Accordingly, some suggestions are proposed to strengthen the stability of cut slopes.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 30 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): José Antonio Schiavon, Cristina de Hollanda Cavalcanti Tsuha, Luc Thorel〈/p〉 〈div xml:lang="en"〉 〈h5〉A b s t r a c t〈/h5〉 〈div〉〈p〉Helical anchors are commonly used in Brazil for guyed transmission towers subjected to static and cyclic wind loads. In most cases, these anchors are installed in tropical residual soil, a micro-structured material in which the shear strength is provided by soil bonding. During installation of a helical anchor, as the helical plate moves downward into the ground, the soil penetrated is sheared and displaced. Consequently, in this type of soil, anchor installation affects the soil shear strength significantly associated with a bonded structure. However, the cyclic responses of helical anchors in this type of structured soils are rarely reported. To address this problem, tests were conducted in a Brazilian residual soil to investigate the monotonic, cyclic and post-cyclic performances of single-helix anchors. Field tests used two instrumented single-helix anchors installed in this typical residual soil of sandstone, which is frequently observed in large areas in the southern Brazil. The testing results indicate that the disturbance caused by the anchor installation affected the monotonic uplift performance markedly. The results of cyclic loading tests also show no significant degradation of helix bearing resistance and reduced displacement accumulation with increasing load cycles. This is perhaps due to the soil improvement caused by previous loading, which then increases the stiffness response of the anchor.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 26 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Mohammadhossein Sadeghiamirshahidi, Stanley J. Vitton〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The stability analysis of an abandoned underground gypsum mine requires the determination of the mine pillar’s strength. This is especially important for flooded abandoned mines where the gypsum pillars become saturated and are subjected to dissolution after flooding. Further, mine pillars are subjected to blast vibrations that generate some level of macro- and micro-fracturing. Testing samples of gypsum must, therefore, simulate these conditions as close as possible. In this research, the strength of gypsum is investigated in an as-received saturated condition using uniaxial compressive strength (UCS), Brazilian tensile strength (BTS) and point load index (PLI) tests. The scale effect was investigated and new correlations were derived to describe the effect of sample size on both UCS and BTS under dry and saturated conditions. Effects of blasting on these parameters were observed and the importance of choosing the proper samples was discussed. Finally, correlations were derived for both compressive and tensile strengths under dry and saturated conditions from the PLI test results, which are commonly used as a simple substitute for the indirect determination of UCS and BTS.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Ioannis Vazaios, Mark S. Diederichs, Nicholas Vlachopoulos〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Rockbursting in deep tunnelling is a complex phenomenon posing significant challenges both at the design and construction stages of an underground excavation within hard rock masses and under high in situ stresses. While local experience, field monitoring, and informed data-rich analysis are some of the tools commonly used to manage the hazards and the associated risks, advanced numerical techniques based on discontinuum modelling have also shown potential in assisting in the assessment of rockbursting. In this study, the hybrid finite-discrete element method (FDEM) is employed to investigate the failure and fracturing processes, and the mechanisms of energy storage and rapid release resulting in bursting, as well as to assess its utility as part of the design process of underground excavations. Following the calibration of the numerical model to simulate a deep excavation in a hard, massive rock mass, discrete fracture network (DFN) geometries are integrated into the model in order to examine the impact of rock structure on rockbursting under high in situ stresses. The obtained analysis results not only highlight the importance of explicitly simulating pre-existing joints within the model, as they affect the mobilised failure mechanisms and the intensity of strain bursting phenomena, but also show how the employed joint network geometry, the field stress conditions, and their interaction influence the extent and depth of the excavation induced damage. Furthermore, a rigorous analysis of the mass and velocity of the ejected rock blocks and comparison of the obtained data with well-established semi-empirical approaches demonstrate the potential of the method to provide realistic estimates of the kinetic energy released during bursting for determining the energy support demand.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Ali Alnedawi, Kali Prasad Nepal, Riyadh Al-Ameri, Mohanad Alabdullah〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Repeated load triaxial test is used to assess the deformation behaviour of unbound granular materials (UGMs) in flexible road pavements. Repeated load pulse characteristics (i.e. shape, loading period and rest period) are the stress configurations used in the experimental set-up to simulate the passing axle loads. Some researchers and standard testing protocols suggest a rest period of varying durations after a loading phase. A thorough review of existing literature and practises has revealed that there is no agreement about the effect of the rest period of vertical stress pulse on the deformation behaviour of the UGMs. Therefore, the main objective of this study is to investigate the effect of repeated stress rest period on the deformation behaviour of UGMs experimentally. Experiments are conducted, both with and without rest period, using basalt and granite crushed rocks from Victoria, Australia. Furthermore, in order to gain insight into the effect of the rest period, finite element modelling is also developed. Both the experimental and modelling results show that the rest period has a noticeable effect on both resilient and permanent deformation behaviours of UGMs. It is, therefore, recommended to take extra precautions while adopting a particular standard testing protocol and to supplement the results by additional tests with different loading configurations.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 3 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): C. Caselle, S. Bonetto, C. Colombero, C. Comina〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The high sedimentological variability of gypsum rocks has the effect that a univocal characterization of this material is not easy to establish. This is particularly true from the geomechanical point of view: when the mechanical properties of gypsum rocks are requested, it is therefore necessary to undertake detailed characterization analyses. Common facies of gypsum was observed in the Upper Miocene evaporitic succession (Messinian Salinity Crisis) within the whole Mediterranean Basin. In this work, mechanical tests were conducted on a site-specific facies, represented by the microcrystalline branching selenite. The tested samples came from the Monferrato area (northwestern Italy). Uniaxial compressive strength (UCS) tests were performed in order to obtain reference mechanical parameters. More rapid and economic point load test (PLT) and ultrasonic pulse velocity (UPV) measurements were additionally performed to verify their applicability as complementary/alternative methods for site characterization. Rock-type specific PLT-UCS and UPV-UCS relationships were established. A wide dispersion of the mechanical parameters was observed due to the heterogeneities of the studied material. Consequently, compositional, textural and microstructural observations on selected samples were performed. Two main material classes were recognized based on average grain size and total gypsum content, underlining the significant influence of the grain sorting on the measured mechanical properties.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 29 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): M.K. Atahu, F. Saathoff, A. Gebissa〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Various factors can affect the durability of roads, such as the strength of sub-grade, the quality of the sub-base and base course, the environments and properties of the soil used. Particularly, roads built on expansive soil are susceptible to early damage due to the swelling and shrinkage characteristics of this kind of soil under changing moisture conditions. The most common technique used to improve the properties of problematic soil is stabilization with additives. Using waste materials to improve the properties of expansive soil is a recent trend in soil stabilization. This study deals with the treatment of expansive soil with coffee husk ash (CHA). Coffee husk is a by-product of coffee production, and CHA is the resulting ash after burning it. In this study, the bearing capacity and compressibility characteristics of expansive soil (specifically black cotton (BC) soil) stabilized with varying percentages of CHA (5%, 10%, 15%, and 20%) are investigated. Then, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) were used to analyze the influence of CHA on surface morphology and chemical composition of the studied soil. The results showed that the soil treated with CHA is generally improved in terms of strength. Addition of 20% CHA increases the bearing capacity of the soil by three-fold. In addition, the morphological studies of the soil samples treated with 10% and 15% CHA indicated the formation of hydrated particles and cementitious compounds as a result of the reaction between the soil and CHA. This indicates the potential usage of CHA as a stabilization agent and subsequently, it can address the disposal and environmental concerns related to coffee husk.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Sajjad Kalantari, Alireza Baghbanan, Hamid Hashemalhosseini〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The small-scale drilling technique can be a fast and reliable method to estimate rock strength parameters. It needs to link the operational drilling parameters and strength properties of rock. The parameters such as bit geometry, bit movement, contact frictions and crushed zone affect the estimated parameters. An analytical model considering operational drilling data and effective parameters can be used for these purposes. In this research, an analytical model was developed based on limit equilibrium of forces in a T-shaped drag bit considering the effective parameters such as bit geometry, crushed zone and contact frictions in drilling process. Based on the model, a method was used to estimate rock strength parameters such as cohesion, internal friction angle and uniaxial compressive strength of different rock types from operational drilling data. Some drilling tests were conducted by a portable and powerful drilling machine which was developed for this work. The obtained results for strength properties of different rock types from the drilling experiments based on the proposed model are in good agreement with the results of standard tests. Experimental results show that the contact friction between the cutting face and rock is close to that between bit end wearing face and rock due to the same bit material. In this case, the strength parameters, especially internal friction angle and cohesion, are estimated only by using a blunt bit drilling data and the bit bluntness does not affect the estimated results.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 31 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Klaus Thoeni, Martin Servin, Scott W. Sloan, Anna Giacomini〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Design of waste rock barriers forming safety berms for haul trucks requires knowledge of complex interactions which cannot readily be tested by physical means. An advanced numerical model based on non-smooth multi-domain mechanics is presented together with model calibration using limited full-scale experimental data. Waste rock is represented by spherical particles with rolling resistance, and an ultra-class haul truck is represented by a rigid multibody system interconnected with mechanical joints. The model components are first calibrated and then the calibrated model is used for simulating various collision scenarios with different approach conditions and safety berm geometries. Numerical predictions indicate that the width of the berm is most critical for efficiently stopping a runaway truck. The model can also predict if a certain berm geometry is capable of stopping a runaway truck. Results are summarised in a series of diagrams intended for use as design guidelines by practitioners and engineers.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Mojtaba Kamani, Rassoul Ajalloeian〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Aggregate degradation (AD) is one of the major reasons accounting for failure of aggregate materials, and the mechanical degradation of aggregate materials can be determined by different test methods. This process basically requires many aggregate samples and special instruments, and thus is time-consuming. The main purpose of this research is to evaluate the possibility of estimating the AD characteristics using rock strength tests and to investigate the relationships between AD properties and rock strength tests. For understanding the relationships, two common rock strength tests are employed, i.e. unconfined compressive strength (UCS) and point load index (PLI) tests. In the tests, the AD properties of 40 kinds of carbonate aggregates sampled from Iran were studied. The AD properties were determined by Los Angeles abrasion value (LAAV), aggregate impact value (AIV) and aggregate crushing value (ACV). Also, the samples are classified according to the strength and rock types, and the effect of this classification is investigated based on the relationship between rock strengths and AD properties. The results indicate that the PLI is better than UCS for evaluation of AD properties. Among rock strength tests, PLI has a closer relationship with AIV (〈em〉R〈/em〉〈sup〉2〈/sup〉 = 0.832). Also, UCS has relative larger effects on the ACV (〈em〉R〈/em〉〈sup〉2〈/sup〉 = 0.812) under the same loading condition. The weakest correlation occurs between LAAV and UCS (〈em〉R〈/em〉〈sup〉2〈/sup〉 = 0.679). In view of the rational AD properties in the predictive procedure, it is possible to predict AD properties based on the strength tests and rock types. The results also show that the prediction of AD properties using rock strength test based on rock types yields better correlations than that using unclassified samples. The classification based on rock types can extrapolate the different relationships of AD prediction from rock strength tests. The results in this context could be used for preliminarily selecting proper rock aggregates with a limit of allowable AD tests for practical applications by PLI.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 20 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Eclesielter Batista Moreira, Jair Arrieta Baldovino, Juliana Lundgren Rose, Ronaldo Luis dos Santos Izzo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉One of the conventional ways to improve the mechanical behavior of soils is to mix them with cementing agents such as cement, lime and fly ash. Recently, introduction to alternative materials or sub-products that can be adopted to improve the soil strength is of paramount importance. Therefore, the present study aims to investigate the effects of porosity (〈em〉η〈/em〉), dry unit weight (〈em〉γ〈/em〉〈sub〉d〈/sub〉) of molding, cement content (〈em〉C〈/em〉) and porosity/volumetric cement content ratio (〈em〉η〈/em〉/〈em〉C〈/em〉〈sub〉iv〈/sub〉) or void/cement ratio on the unconfined compressive strength (〈em〉q〈/em〉〈sub〉u〈/sub〉 or UCS) of silty soil–roof tile waste (RT) mixtures. Soil samples are molded into four different dry unit weights (i.e. 13 kN/m〈sup〉3〈/sup〉, 13.67 kN/m〈sup〉3〈/sup〉, 14.33 kN/m〈sup〉3〈/sup〉 and 15 kN/m〈sup〉3〈/sup〉) using 3%, 6% and 9% cement and 5%, 15% and 30% RT. The results show that with the addition of cement, the strength of the RT–soil mixtures increases in a linear manner. On the other hand, the addition of RT decreases 〈em〉q〈/em〉〈sub〉u〈/sub〉 of the samples at a constant percentage of cement, and the decrease in porosity can increase 〈em〉q〈/em〉〈sub〉u〈/sub〉. A dosage equation is derived from the experimental data using the porosity/volumetric cement content ratio (〈em〉η〈/em〉/〈em〉C〈/em〉〈sub〉iv〈/sub〉) where the control variables are the moisture content, crushed tile content, cement content and porosity.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 20 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Changbing Qin, Siau Chen Chian〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper presents a procedure for assessing the reinforcement force of geosynthetics required for maintaining dynamic stability of a steep soil slope. Such a procedure is achieved with the use of the discretization technique and kinematic analysis of plasticity theory, i.e. discretization-based kinematic analysis. The discretization technique allows discretization of the analyzed slope into various components and generation of a kinematically admissible failure mechanism based on an associated flow rule. Accordingly, variations in soil properties including soil cohesion, internal friction angle and unit weight are accounted for with ease, while the conventional kinematic analysis fails to consider the changes in soil properties. The spatial–temporal effects of dynamic accelerations represented by primary and shear seismic waves are considered using the pseudo-dynamic approach. In the presence of geosynthetic reinforcement, tensile failure is discussed providing that the geosynthetics are installed with sufficient length. Equating the total rates of work done by external forces to the internal rates of work yields the upper bound solution of required reinforcement force, below which slopes fail. The reinforcement force is sought by optimizing the objective function with regard to independent variables, and presented in a normalized form. Pseudo-static analysis is a special case and hence readily transformed from pseudo-dynamic analysis. Comparisons of the pseudo-static/dynamic solutions calculated in this study are highlighted. Although the pseudo-static approach yields a conservative solution, its ability to give a reasonable result is substantiated for steep slopes. In order to provide a more meaningful solution to a stability analysis, the pseudo-dynamic approach is recommended due to considerations of spatial–temporal effect of earthquake input.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Lamine Boumaiza, Ali Saeidi, Marco Quirion〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The most commonly used method for assessing the hydraulic erodibility of rock is Annandale's method. This method is based on a correlation between the erosive force of flowing water and the capacity of rock resistance. This capacity is evaluated using Kirsten's index, which was initially developed to evaluate the excavatability of earth materials. For rocky material, this index is determined according to certain geomechanical factors related to intact rock and rock mass, such as compressive strength of intact rock, rock block size, discontinuity shear strength and relative block structure. To quantify the relative block structure, Kirsten (1982) developed a mathematical expression that accounts for the shape and orientation of the blocks relative to the direction of flow. Kirsten's initial concept for assessing the relative block structure considers that the geological formation is mainly fractured by two joint sets forming an orthogonally fractured system. An adjusted concept is proposed to determine the relative block structure when the fractured system is non-orthogonal where the angle between the planes of the two joint sets is greater or less than 90°. An analysis of the proposed relative block structure rating shows that considering a non-orthogonally fractured system has a significant effect on Kirsten's index and, as a consequence, on the assessment of the hydraulic erodibility of rock.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 25 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Richeng Liu, Sha Lou, Xiaojing Li, Guansheng Han, Yujing Jiang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this context, we experimentally studied the anisotropic mechanical behaviors of rough-walled plaster joints using a servo-controlled direct shear apparatus under both constant normal load (CNL) and constant normal stiffness (CNS) conditions. The shear-induced variations in the normal displacement, shear stress, normal stress and sheared-off asperity mass are analyzed and correlated with the inclination angle of the critical waviness of joint surfaces. The results show that CNS condition gives rise to a smaller normal displacement due to the larger normal stress during shearing, compared with CNL condition. Under CNL conditions, there is one peak shear stress during shearing, whereas there are no peak shear stress for some cases and two peaks for other cases under CNS conditions depending on the geometry of joint surfaces. The inclination angle of the critical waviness has been verified to be capable of describing the joint surface roughness and anisotropy. The joint surface is more significantly damaged under CNS conditions than that under CNL conditions. With increment of the inclination angle of the critical waviness, both the normal displacement and sheared-off asperity mass increase, following power law functions; yet the coefficient of determination under CNL conditions is larger than that under CNS conditions. This is because the CNS condition significantly decreases the inclination angle of the critical waviness during shearing due to the larger degree of asperity degradation.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 8 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Ali Alnedawi, Riyadh Al-Ameri, Kali Prasad Nepal〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Several available mechanistic-empirical pavement design methods fail to include predictive model for permanent deformation (PD) of unbound granular materials (UGMs), which make these methods more conservative. In addition, there are limited regression models capable of predicting the PD under multi-stress levels, and these models have regression limitations and generally fail to cover the complexity of UGM behaviour. Recent researches are focused on using new methods of computational intelligence systems to address the problems, such as artificial neural network (ANN). In this context, we aim to develop an artificial neural model to predict the PD of UGMs exposed to repeated loads. Extensive repeated load triaxial tests (RLTTs) were conducted on base and subbase materials locally available in Victoria, Australia to investigate the PD properties of the tested materials and to prepare the database of the neural networks. Specimens were prepared over different moisture contents and gradations to cover a wide testing matrix. The ANN model consists of one input layer with five neurons, one hidden layer with twelve neurons, and one output layer with one neuron. The five inputs were the number of load cycles, deviatoric stress, moisture content, coefficient of uniformity, and coefficient of curvature. The sensitivity analysis showed that the most important indicator that impacts PD is the number of load cycles with influence factor of 41%. It shows that the ANN method is rapid and efficient to predict the PD, which could be implemented in the Austroads pavement design method.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 20 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): L.B. McQueen, A. Purwodihardjo, S.V.L. Barrett〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉This paper explores the potential implications of recent thinking in relation to rock mass strength for future tunnelling projects in Brisbane, Australia, as they are constructed within deep horizons where the in situ stress magnitudes is larger. Rock mass failure mechanisms for the current tunnels in Brisbane are generally discontinuity controlled and the potential for stress-induced failure is relatively rare. For the road tunnels which have been constructed in Brisbane over the last 12 years, the strength of the more massive rock masses for continuum analysis has been estimated by the application of the Hoek-Brown (H-B) failure criterion using the geological strength index (GSI) to determine the H-B parameters 〈em〉m〈/em〉〈sub〉b〈/sub〉, 〈em〉s〈/em〉 and 〈em〉a〈/em〉. Over the last few years, alternative approaches to estimating rock mass strength for ‘massive to moderately jointed hard rock masses’ have been proposed by others, which are built on the work completed by Hoek and Brown in this area over their joint careers. This paper explores one of these alternative approaches to estimating rock mass strength for one of the geological units (the Brisbane tuff), which is often encountered in tunnelling projects in Brisbane. The potential implications of these strength forecasts for future tunnelling projects are discussed along with the additional work which will need to be undertaken to confirm the applicability of such alternative strength criteria for this rock mass.〈/p〉 〈p〉© 2019 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (〈a href="https://creativecommons.org/licenses/by-nc-nd/4.0/" target="_blank"〉http://creativecommons.org/licenses/by-nc-nd/4.0/〈/a〉).〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 20 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Manchao He, L. Ribeiro e Sousa, André Müller, Eurípedes Vargas, R.L. Sousa, C. Sousa Oliveira, Weili Gong〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The 2008 Wenchuan earthquake resulted in a large number of fatalities and caused significant economic losses. Thousands of landslides, many of which are very large, were triggered by the earthquake. A majority of catastrophic landslides were distributed along the central Longmenshan fault system, at the eastern margin of the Tibetan Plateau. Some of the landslides resulted in sudden damming of rivers causing flooding, which in turn induced secondary sliding disasters. Among the most significant landslides, the Daguangbao landslide was the largest in volume with the maximum thickness. For this, a numerical model of the Daguangbao landslide, using the material point method (MPM), was developed to simulate the interaction of the seismic loads imposed on the slope. The numerical results then are compared with the post-earthquake profile. As a consequence of the landslide, a nearly vertical head scarp with a maximum height of about 700 m was generated. This is considered as a high risk situation that requires constant monitoring and evaluation. Finally, we propose a methodology based on Bayesian networks (BNs) to manage the risk associated with the stability of the rockwall at the Daguangbao landslide site.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 5 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): A. Rouabhi, P. Labaune, M. Tijani, N. Gatelier, G. Hévin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Recently, stress-based dilatancy criteria have become essential tools to design underground facilities in salt formations such as gas storage caverns. However, these criteria can depend critically on the volumetric strain measurements used to deduce the dilatancy onset. Results from conventional triaxial compression can show different volumetric behavior depending on the loading conditions, as well as on the measurement techniques. In order to obtain a quantitative understanding of this problem, an experimental program was carried out and the testing procedure was investigated numerically under homogeneous and heterogeneous stress states. The experimental results showed that the deviatoric stress corresponding to the dilatancy onset was significantly dependent on the measurement techniques. With a heterogeneous stress state, the simulation results revealed that the strain measurements at different scales (referred in this paper as local, hybrid or global) can provide different volumetric results with moderate to significant deviations from the idealized behavior, and hence different onset of dilatancy. They also proved that, under low confinement, tensile stresses can take place within the compressed specimen leading to a great deviation of the dilatancy onset from the idealized behavior. From both experimental and numerical investigations, the difference in sensitivity to the measurement techniques between the deviatoric and the volumetric behaviors is explained by the relatively small values of the volumetric strain. The non-ideal laboratory conditions have more impact on this strain than on the deviatoric one. These findings can have implications for the interpretation of the dilatancy behavior of rock salt, and hence on the geomechanical design aspects in salt formations.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 22 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Duaa Al-Jeznawi, Marcelo Sanchez, Abbas J. Al-Taie, Marcin Zielinski〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soil curling is an important phenomenon associated with volume changes induced by increasing soil suction upon desiccation. The study of soil behaviors associated with drying in soils (e.g. soil shrinkage, desiccation cracks and curling) has received increasing attention over the last few years, which has been mainly driven by the forecast climate change that will warm up our planet. There are significant gaps in the current knowledge related to the factors that control the development of curling deformations in soils. For this, the curling phenomenon is investigated through laboratory desiccation tests on different mixtures of artificial soils. The effects of soil grain size distribution, mineralogy, soil microstructure, and soil water content on the curling deformation are analyzed. Digital photos were taken at regular time intervals during the tests to understand the volume changes in the soil samples during drying. It is found that soil fabric and soil water content have significant effects on curling scenario. It is observed that the percentage of sand particles and the initial water content play a critical role in the development of soil curling. Samples of pure clayey minerals experienced shrinkage without or with minor curling during drying.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 23 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Ch.Vijaya Kumar, Harsha Vardha, Ch.S.N. Murthy, N.C. Karmakar〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In many engineering applications such as mining, geotechnical and petroleum industries, drilling operation is widely used. The drilling operation produces sound by-product, which could be helpful for preliminary estimation of the rock properties. Nevertheless, determination of rock properties is very difficult by the conventional methods in terms of high accuracy, and thus it is expensive and time-consuming. In this context, a new technique was developed based on the estimation of rock properties using dominant frequencies from sound pressure level generated during diamond core drilling operations. First, sound pressure level was recorded and sound signals of these sound frequencies were analyzed using fast Fourier transform (FFT). Rock drilling experiments were performed on five different types of rock samples using computer numerical control (CNC) drilling machine BMV 45 T20. Using simple linear regression analysis, mathematical equations were developed for various rock properties, i.e. uniaxial compressive strength, Brazilian tensile strength, density, and dominant frequencies of sound pressure level. The developed models can be utilized at early stage of design to predict rock properties.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 23 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): T. Voake, A. Nermoen, R.I. Korsnes, I.L. Fabricius〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Temperature history can have a significant effect on the strength of water-saturated chalk. In this study, hydrostatic stress cycles are applied to understand the mechanical response of chalk samples exposed to temperature cycling between each stress cycle, compared to the samples tested at a constant temperature. The total accumulated strain during a stress cycle and the irreversible strain are reported. Chalk samples from Kansas (USA) and Mons (Belgium), with different degrees of induration (i.e. amount of contact cementation), were used. The samples were saturated with equilibrated water (polar) and non-polar Isopar H oil to quantify water weakening. All samples tested during 10 stress cycles with varying temperature (i.e. temperature cycled in between each stress cycle) accumulated more strain than those tested at constant temperatures. All the stress cycles were performed at 30 °C. The two chalk types behaved similarly when saturated with Isopar H oil, but differently when saturated with water. When saturated with water, the stronger Kansas chalk accumulated more total strain and more irreversible strain within each stress cycle than the weaker Mons chalk.〈/p〉 〈p〉© 2018 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (〈a href="https://creativecommons.org/licenses/by-nc-nd/4.0/" target="_blank"〉http://creativecommons.org/licenses/by-nc-nd/4.0/〈/a〉).〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 19 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): I. Vazaios, N. Vlachopoulos, M.S. Diederichs〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Deep underground excavations within hard rocks can result in damage to the surrounding rock mass mostly due to redistribution of stresses. Especially within rock masses with non-persistent joints, the role of the pre-existing joints in the damage evolution around the underground opening is of critical importance as they govern the fracturing mechanisms and influence the brittle responses of these hard rock masses under highly anisotropic in situ stresses. In this study, the main focus is the impact of joint network geometry, joint strength and applied field stresses on the rock mass behaviours and the evolution of excavation induced damage due to the loss of confinement as a tunnel face advances. Analysis of such a phenomenon was conducted using the finite-discrete element method (FDEM). The numerical model is initially calibrated in order to match the behaviour of the fracture-free, massive Lac du Bonnet granite during the excavation of the Underground Research Laboratory (URL) Test Tunnel, Canada. The influence of the pre-existing joints on the rock mass response during excavation is investigated by integrating discrete fracture networks (DFNs) of various characteristics into the numerical models under varying in situ stresses. The numerical results obtained highlight the significance of the pre-existing joints on the reduction of in situ rock mass strength and its capacity for extension with both factors controlling the brittle response of the material. Furthermore, the impact of spatial distribution of natural joints on the stability of an underground excavation is discussed, as well as the potentially minor influence of joint strength on the stress induced damage within joint systems of a non-persistent nature under specific conditions. Additionally, the in situ stress-joint network interaction is examined, revealing the complex fracturing mechanisms that may lead to uncontrolled fracture propagation that compromises the overall stability of an underground excavation.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 28 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Sevda Dehkhoda, Bryce Hill〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper investigates the effect of cutter clearance angle on variation of depth of cut and cutting process with an Actuated Disc Cutting (ADC). ADC is a cyclic cutting method with two main characteristics: i) a disk-shape cutter is used to attack the rock in an undercutting mechanism; ii) the cutter is dynamically actuated as it is moved across the rock. Hence, the cutting process of such system is periodic, each recurrence known as actuation cycle. The first ADC model (Dehkhoda and Detournay, 2017) represented an idealization of the technology with a flat disc cutter, where no clearance angle was considered. The evolution of the contact between the disc and the rock was, therefore, computed only on horizontal 〈em〉x〈/em〉-〈em〉y〈/em〉 plane, ignoring the effect of normal component of the force acting on cartridge. This article reports on a study that incorporates the cutter inclination angle in derivation of cutter/rock interface laws. It extends the proposed kinematic and geometry based model to take into account the variable depth of cut in estimating the forces associated with cutting in one actuation cycle. Experiments were conducted using Wobble to test the predictions of the improved model at various operating conditions. The model predictions are matched with the experiment results and effects of various factors are analyzed.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 10 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Suraparb Keawsawasvong, Boonchai Ukritchon〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A parametric study of undrained stability of a spherical cavity in clays is investigated by finite element limit analysis with an axisymmetric condition. Influences of cover depth ratio of cavity and dimensionless overburden factor on predicted failure mechanisms and dimensionless load factor are examined. It is found that a previously recommended and up-to-date lower bound solution to the problem was significantly inaccurate for practice use. Thus, an accurate approximate solution to the problem is proposed from nonlinear regression analysis of the computed average bound solutions. New cavity stability factors for the soil cohesion and soil unit weight are proposed. New findings are revealed for the three-dimensional effect of the cavity shape on these factors between the axisymmetric and plane strain conditions, and their applications to the undrained stability evaluation of cavity problems in practice are described.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 9 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Aditya Singh, K. Seshagiri Rao, Ramanathan Ayothiraman〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Deep wellbores/boreholes are generally drilled into rocks for oil and gas exploration, monitoring of tectonic stresses purposes. Wellbore and tunnel in depth are generally in true triaxial stress state, even if the ground is under axisymmetric loading condition. Stability of such wellbores is very critical and collapse of wellbore must be avoided. Mogi-Coulomb failure criterion is a better representation of rock strength under true triaxial condition. In this paper, an analytical solution is proposed using Mogi-Coulomb failure criterion. The solution is obtained for rock mass exhibiting elastic-perfectly plastic or elastic-brittle-plastic behaviour considering in-plane isotropic stresses. The proposed solution is then compared with exact analytical solution for incompressible material and experimental results of thick-wall cylinder. It is shown that the results obtained by the proposed analytical solution are in good agreement with the experimental results and exact analytical solution. A reduction of about 13%–20% in plastic zone from the proposed closed-form solution is observed, as compared to the results from the finite element method (FEM) based Mohr-Coulomb criterion. Next, the influences of various parameters such as Poisson's ratio, internal pressure (mud weight), dilation angle, and out-of-plane stress are studied in terms of stress and deformation responses of wellbore. The results of the parametric study reveal that variation in the out-of-plane stress has an inverse relation with the radius of plastic zone. Poisson's ratio does not have an appreciable influence on the tangential stress, radial stress and radial deformation. Dilation angle has a direct relation with the deformation. Internal pressure is found to have an inverse relation with the radial deformation and the radius of plastic zone.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 10 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Wei Yao, Kaiwen Xia〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Rocks are increasingly used in extreme environments characterized by high loading rates and high confining pressures. Thus the fracture properties of rocks under dynamic loading and confinements are critically important in various rock mechanics and rock engineering problems. Due to the transient nature of dynamic loading, the dynamic fracture tests of rocks are much more challenging than their static counterparts. Understanding the dynamic fracture behavior of geomaterials relies significantly on suitable and reliable dynamic fracture testing methods. One of such methods is the notched semi-circle bend (NSCB) test combined with the advanced split Hopkinson pressure bar (SHPB) system, which has been recommended by the International Society for Rock Mechanics and Rock Engineering (ISRM) as the standard method for determination of dynamic fracture toughness. The dynamic NSCB-SHPB method can provide detailed insights into dynamic fracture properties including initiation fracture toughness, fracture energy, propagation fracture toughness and fracture velocity. This review aims to fully describe the detailed principles and state-of-the-art of applications of dynamic NSCB-SHPB techniques. The history and principles of dynamic NSCB-SHPB tests for rocks are outlined, and then the applications of dynamic NSCB-SHPB method (including the measurements of initiation and propagation fracture toughnesses and the limiting fracture velocity, the size effect and the digital image correlation (DIC) experiments) are discussed. Further, other applications of dynamic NSCB-SHPB techniques (i.e. the thermal, moisture and anisotropy effects on the dynamic fracture properties of geomaterials, and dynamic fracture toughness of geomaterials under pre-loading and hydrostatic pressures) are presented.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 10 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Philippe Morissette, John Hadjigeorgiou〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉There are considerable challenges associated with the design of ground support for seismically-active underground mines. It is extremely difficult to establish the demand on ground support as well as the capacity of a ground support system. The resulting dynamic or impact loads caused by mining-induced seismicity are difficult to anticipate and quantify. The performance of a ground support system is defined by the load distribution and interaction between several reinforcement and surface support elements. Consequently, the design of ground support in seismically-active mines tends to evolve, or be modified based on qualitative assessments of perceived performance or response to significant seismic events or rockbursts. This research is motivated by a need to provide quantitative and data-driven design guidelines for ground support systems subjected to dynamic-loading conditions. Rockburst data were collected from three deep and seismically-active underground mines in the Sudbury basin in Canada. The constructed database comprises 209 seismic events that resulted in damage to mine excavations and ground support. These events were associated with damage at 324 locations within the three mines. The developed ground support design strategy, based on these documented case studies, identifies areas where the use of dynamic or enhanced support should be employed. The developed design methodology provides guidelines for the zoning of mine locations in which installation of enhanced support is recommended, the specifications for an optimal ground support system, and the timing or sequence of installation.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 8 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Onur Vardar, Chengguo Zhang, Ismet Canbulat, Bruce Hebblewhite〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Coal burst is a manifestation of rapid energy release, which is considered as one of the most critical operational hazards in underground coal mines. This study numerically investigates the effects of discontinuities on the strength and energy release characteristics of coal mass samples under uniaxial compression. The universal distinct element code (UDEC) was used to model pillar-scale coal mass samples that were represented by an assembly of triangular deformable blocks, and pre-existing discontinuities such as bedding planes and cleats were also included in the models. It shows that cleat spacing can have a significant impact on compressive strength and energy release, with both strength and energy release (magnitude and rate) reducing as the number of cleats was increased. This work is one of the first attempts to numerically model and quantify the energy release which occurs during the failure of pillar-scale coal mass samples with varying cleat densities. The insights from the numerical modelling can help to understand the possible energy release mechanisms and associated coal burst potential in changing coal cleat conditions.〈/p〉 〈p〉© 2019 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (〈a href="https://creativecommons.org/licenses/by-nc-nd/4.0/" target="_blank"〉http://creativecommons.org/licenses/by-nc-nd/4.0/〈/a〉).〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 12 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Divya Shaunik, Mahendra Singh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Constructions in the field of civil engineering basically need to deal with rocks. Strength behaviour of rock intersected by a discontinuity or a set of discontinuities has been a hot topic for engineering and research community. The popular attributes of discontinuities that have been given due importance are their frequency, orientation and surface characteristics. Non-persistency joints, however, have been received little attention. This article presents an experimental study wherein focus has been made on the effect of non-persistency of the joint on the uniaxial compressive strength (UCS) of a model rock for various geometries such as orientation, discontinuity length ratio and number of joint segments. The applicability of single plane of weakness theory (SPWT) to assess the strength of jointed specimens has also been evaluated. It has been noticed that SPWT captures the strength behaviour only for a narrow range of discontinuity orientations. As an improvement, an approach is suggested by extending concepts of degree of persistence and joint factor to have a better understanding towards strength behaviour of rocks intersected by non-persistent joints.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 19 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Aria Mardalizad, Marco Caruso, Andrea Manes, Marco Giglio〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The mechanical behaviour of a quasi-brittle material, i.e. Pietra Serena sandstone, was investigated both numerically and experimentally in order to build a reliable numerical modelling system applicable to more complex cases. The Karagozian and Case concrete (KCC) model was exploited as the material constitutive law and a new method to utilise this model for efficient and accurate simulation of quasi-brittle materials is discussed. The capability of this model is evaluated by comparing the results of the numerical simulations with the corresponding experimental results, and the method itself is critically assessed.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 31 May 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): F. Ouchterlony, J.A. Sanchidrián〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The paper reviews the development of prediction formulas for the fragmentation from bench blasting. Much attention has been paid to the Kuz-Ram model, its development and errors, and the mean vs. median misunderstanding. The work by the US Bureau of Mines (USBM) and Chung and Katsabanis are also reviewed, as well as the two Julius Kruttschnitt Mineral Research Centre (JKMRC) models, i.e. the crush zone model (CZM) and the two-component model (TCM), which were developed to cope with the underestimation of blasting fines. The change brought by the Swebrec distribution and the associated Kuznetsov-Cunningham-Ouchterlony (KCO) model is described. Studying distribution-free fragment sizes 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈msub〉〈mrow〉〈mi〉x〈/mi〉〈/mrow〉〈mrow〉〈mi〉P〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 for an arbitrary mass passing 〈em〉P〈/em〉 led to the discovery of the fragmentation-energy fan, and with the help of dimensional analysis, to the new fragmentation prediction model 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈msub〉〈mrow〉〈mi〉x〈/mi〉〈/mrow〉〈mrow〉〈mi〉P〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉-frag, which has much lower errors than those of the Kuz-Ram and CZM models.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 30 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Krishna Kanta Panthi, Chhatra Bahadur Basnet〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In situ stress condition in rock mass is influenced by both tectonic activity and geological environment such as faulting and shearing in the rock mass. This influence is of significance in the Himalayan region, where the tectonic movement is active, resulting in periodic dynamic earthquakes. Each large-scale earthquake causes both accumulation and sudden release of strain energy, instigating changes in the in situ stress environment in the rock mass. This paper first highlights the importance of the magnitude of the minimum principal stress in the design of unlined or shotcrete lined pressure tunnel as water conveyance system used for hydropower schemes. Then we evaluated the influence of local shear faults on the magnitude of the minimum principal stress along the shotcrete lined high pressure tunnel of Upper Tamakoshi Hydroelectric Project (UTHP) in Nepal. A detailed assessment of the in situ stress state is carried out using both measured data and three-dimensional (3D) numerical analyses with FLAC〈sup〉3D〈/sup〉. Finally, analysis is carried out on the possible changes in the magnitude of the minimum principal stress in the rock mass caused by seismic movement (dynamic loading). A permanent change in the stress state at and nearby the area of shear zones along the tunnel alignment is found to be an eminent process.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 30 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): C. Drover, E. Villaescusa〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A novel design of development face destress blasting was implemented during the construction of an experimental tunnel at great depth. A second tunnel was developed nearby using conventional blasting as a control. The tunnels were developed parallel to one another and perpendicular to a high sub-horizontal stress. High resolution seismic monitoring was used to record and compare the seismic response generated by each excavation. Analysis of the seismic data from the conventionally-blasted tunnel indicated that the seismogenic zone of stress-driven instability extended up to 3.6 m ahead of the face. Destress blasting within the corresponding zone of the adjacent tunnel had the effect of reducing the rock mass stiffness, primarily due to weakening of the pre-existing natural discontinuities. The reduction in rock mass stiffness was inferred from the spatial broadening of the seismogenic zone and associated reduction in the measured spatial density of events, radiated energy and seismic potency ahead of the face. High strain gradients around the unsupported portion of the conventionally blasted excavation were implied by the rate at which the spatial density of seismicity changed with respect to the tunnel face position. In contrast, the change in the spatial density of seismicity around the destressed development face was much more gradual. This was indicative of lower strain gradients in the rock there. A reduction in rock mass stiffness following destress blasting was also indicated by the much wider variety of seismic source mechanisms recorded adjacent to the destressed tunnel. Seismic source mechanisms associated with destress blasting were also more clearly characteristic of compressive overstressing with fracture closure. The source mechanism data also indicated that destress blasting induced instability on all natural joint sets. When compared to conventional development blasting, destress blasting typically reduced violent strain energy release from the rock mass and the associated seismicity, but not always.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 30 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Ö. Aydan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Rockburst, earthquake and blasting cause some dynamic loads on rock support and rock reinforcement system. Elements of rock support and rock reinforcement are generally made of steel bar or cables, which are resistant against corrosion. These support elements may be subjected to vibrations induced by turbines, vehicle traffic and long-term corrosion in addition to dynamic loading caused by earthquake, rockburst and blasting. In this study, some theoretical, numerical and experimental studies are conducted on rockbolts and rock anchors under shaking and impulsive loading. Then the outcomes of these studies are presented and their practical implications are discussed accordingly.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 27 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Morteza Nejati, Marie Luise Texas Dambly, Martin O. Saar〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉This paper introduces a new methodology to measure the elastic constants of transversely isotropic rocks from a single uniaxial compression test. We first give the mathematical proof that a uniaxial compression test provides only four independent strain equations. As a result, the exact determination of all five independent elastic constants from only one test is not possible. An approximate determination of the Young’s moduli and the Poisson’s ratios is however practical and efficient when adding the Saint-Venant relation as the fifth equation. Explicit formulae are then developed to calculate both secant and tangent definitions of the five elastic constants from a minimum of four strain measurements. The results of this new methodology applied on three granitic samples demonstrate a significant stress-induced nonlinear behavior, where the tangent moduli increase by a factor of three to four when the rock is loaded up to 20 MPa. The static elastic constants obtained from the uniaxial compression test are also found to be significantly smaller than the dynamic ones obtained from the ultrasonic measurements.〈/p〉 〈p〉© 2019 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (〈a href="https://creativecommons.org/licenses/by-nc-nd/4.0/" target="_blank"〉http://creativecommons.org/licenses/by-nc-nd/4.0/〈/a〉).〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 13 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Jair de Jesús Arrieta Baldovino, Ronaldo Luis dos Santos Izzo, Eclesielter Batista Moreira, Juliana Lundgren Rose〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉In the present study, unconfined compressive strength (〈em〉q〈/em〉〈sub〉u〈/sub〉) values of two lime-treated soils (soil 1 and 2) with curing times of 28 d, 90 d and 360 d were optimized. The influence of void/lime ratio was represented by the porosity/volumetric lime content ratio (〈em〉η〈/em〉/〈em〉L〈/em〉〈sub〉iv〈/sub〉) as the main parameter. 〈em〉η〈/em〉/〈em〉L〈/em〉〈sub〉iv〈/sub〉 represents the volume of void influenced by compaction effort and lime volume. The evolution of 〈em〉q〈/em〉〈sub〉u〈/sub〉 was analyzed for each soil using the coefficient of determination as the optimization parameter. Aiming at providing adjustments to the mechanical resistance values, the 〈em〉η〈/em〉/〈em〉L〈/em〉〈sub〉iv〈/sub〉 parameter was modified to 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mi〉η〈/mi〉〈mo linebreak="badbreak"〉/〈/mo〉〈msubsup〉〈mi〉L〈/mi〉〈mrow〉〈mtext〉iv〈/mtext〉〈/mrow〉〈mi〉C〈/mi〉〈/msubsup〉〈/mrow〉〈/math〉 using the adjustment exponent 〈em〉C〈/em〉 (to make 〈em〉q〈/em〉〈sub〉u〈/sub〉-〈em〉η〈/em〉/〈em〉L〈/em〉〈sub〉iv〈/sub〉 variation rates compatible). The results show that with the decrease of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"〉〈mrow〉〈mi〉η〈/mi〉〈mo linebreak="badbreak"〉/〈/mo〉〈msubsup〉〈mi〉L〈/mi〉〈mrow〉〈mtext〉iv〈/mtext〉〈/mrow〉〈mi〉C〈/mi〉〈/msubsup〉〈mo〉,〈/mo〉〈/mrow〉〈/math〉 〈em〉q〈/em〉〈sub〉u〈/sub〉 increases potentially and the optimized values of 〈em〉C〈/em〉 were 0.14-0.18. The mechanical resistance data show similar trends between 〈em〉q〈/em〉〈sub〉u〈/sub〉 and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mi〉η〈/mi〉〈mo linebreak="badbreak"〉/〈/mo〉〈msubsup〉〈mi〉L〈/mi〉〈mrow〉〈mtext〉iv〈/mtext〉〈/mrow〉〈mi〉C〈/mi〉〈/msubsup〉〈/mrow〉〈/math〉 for the studied silty soil-ground lime mixtures, which were cured at ambient temperature (23 ± 2) °C with different curing times of 28–360 d. Finally, optimized equations were presented using the normalized strengths and the proposed optimization model, which show 6% error and 95% acceptability on average.〈/p〉 〈p〉© 2019 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 3〈/p〉 〈p〉Author(s): Qihu Qian〈/p〉

Beschreibung: 〈p〉Publication date: Available online 7 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Tetsuji Okada, Tomohiro Naya〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The dynamic shear strength of rocks is required for the earthquake-resistant design of nuclear power plants in Japan. This research aims to propose a mathematical model for estimating the dynamic strength and to validate the model. Two different types of specimens were prepared for the model validation, and the monotonic and cyclic loading tests were conducted to obtain the mathematical model parameters. Subsequently, multistep cyclic loading tests were performed, followed by simulations using the mathematical model. The test results demonstrated that the dynamic shear strength exceeded the static shear strength, which agreed with previous researches. Furthermore, the dynamic shear strength calculated using the mathematical model was generally consistent with that obtained from the experimental data.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 26 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Bhagya Jayasinghe, Zhiye Zhao, Anthony Goh Teck Chee, Hongyuan Zhou, Yilin Gui〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Blasting has been widely used in mining and construction industries for rock breaking. This paper presents the results of a series of field tests conducted to investigate the ground wave propagation through mixed geological media. The tests were conducted at a site in the northwestern part of Singapore composed of residual soil and granitic rock. The field test aims to provide measurement data to better understand the stress wave propagation in soil/rock and along their interface. Triaxial accelerometers were used for the free field vibration monitoring. The measured results are presented and discussed, and empirical formulae for predicting peak particle velocity (PPV) attenuation along the ground surface and in soil/rock were derived from the measured data. Also, the ground vibration attenuation across the soil-rock interface was carefully examined, and it was found that the PPV of ground vibration was decreased by 37.2% when it travels from rock to soil in the vertical direction.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 21 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Heraldo Luiz Giacheti, Roger Augusto Rodrigues, Renan Cravera Bezerra, Breno Padovezi Rocha〈/p〉 〈div xml:lang="en"〉〈div〉〈p〉Interpröetation of electric cone penetration test (CPT) based pore water pressure measurement (CPTu) is well established for soils with behavior that follows classical soil mechanics. The literature on the interpretation of these tests performed on unsaturated tropical soils is limited, and little is known about the influence of soil suction on in situ test data. In this context, the CPT data are presented and discussed to illustrate the seasonal variability in an unsaturated tropical soil site. The test data show that soil suction significantly influenced CPT data up to a depth of 4 m at the study site. It shows the importance of considering seasonal variability in unsaturated soil sites caused by soil suction, which was related to water content through a soil-water retention curve (SWRC). It is also important to consider this aspect in the interpretation of CPT data from these soils.〈/p〉〈/div〉〈/div〉

Beschreibung: 〈p〉Publication date: Available online 5 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Xia-Ting Feng, Yang-Yi Zhou, Quan Jiang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Rock mechanics plays a critical role in the design and construction of hydroelectric projects including large caverns under high in situ stress, deep tunnels with overburden more than 2500 m, and excavated rock slopes of 700 m in height. For this, this paper conducts a review on the rock mechanics contributions to recent hydroelectric developments in China. It includes the development of new testing facilities, mechanical models, recognition methods for mechanical parameters of rock masses, design flowchart and modelling approaches, cracking-restraint method, governing flowchart of rock engineering risk factors enabling the development of risk-reduced design and risk-reduced construction, and initial and dynamic design methods. As an example, the optimal design of underground powerhouses at the Baihetan hydroelectric plant, China, is given. This includes determination of in situ stresses, prediction of deformation and failure depth of surrounding rock masses, development of the optimal excavation scheme and support design. In situ monitoring results of the displacements and excavation damaged zones (EDZs) have verified the rationality of the design methodology.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 28 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): T. Voake, A. Nermoen, C. Ravnås, R.I. Korsnes, I.L. Fabricius〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Calcite has a highly anisotropic thermal expansion coefficient, and repeated heating and cooling cycles can potentially destabilize chalks by breaking cement bonds between neighboring particles. Based on tensile strength measurements, we investigated how temperature cycles induce weakening of chalk. Tensile strength tests were performed on chalk specimens sampled from Kansas (USA) and Mons (Belgium), each with differing amounts of contact cement. Samples of the two chalk types were tested in dry and water-saturated states, and then exposed to 0, 15, and 30 temperature cycles in order to find out under what circumstances thermally induced tensile strength reduction occurs. The testing results show that the dry samples were not influenced by temperature cycling in either of the chalk types. However, in the water-saturated state, tensile strength is increasingly reduced with progressive numbers of temperature cycles for both chalk samples, especially for the more cemented Kansas chalk. The Kansas chalk demonstrated higher initial tensile strength compared to the less cemented Mons chalk, but the strength of both chalks was reduced by the same relative proportion when undergoing thermal cycles in the water-saturated state.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 26 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Giovanni Spagnoli, Satoru Shimobe〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉More than 500 datasets from the literature have been used to evaluate the relationships of specific surface area (SSA), cation exchange capacity (CEC) and activity versus the liquid limit (LL). The correlations gave 〈em〉R〈/em〉〈sup〉2〈/sup〉 values ranging between 0.71 and 0.92. Independent data were also used to validate the correlations. Estimated SSA values slightly overestimate the measured SSA up to 100 m〈sup〉2〈/sup〉/g. Regarding the estimated CEC values, they overestimated the measured CEC values up to 20 meq/(100 g). A probabilistic approach was performed for the correlations of SSA, CEC and activity versus LL. The analysis shows that the relations of SSA, CEC and activity with LL are robust. Using the LL values, it is possible to assess other basic engineering properties of clays.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 26 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Amir Alipour, Abolfazl Eslami〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, design, re-design, and performance of a long-standing very deep excavation, which was originally planned to depth of 38 m, are presented. Over-digging was not planned in the original design, thus the reassessment was performed. Two main topics were followed: deepening to increase the maximum depth of an existent excavation from 38 m to 42.5 m, and feasibility for upgrading a predesigned support system from temporary to permanent support system. The geological investigations in the project site illustrated a type of stiff and cemented coarse-grained alluvium. An observational approach with additional geotechnical investigations and in situ tests was applied. Back analyses of stability of an unsupported access ramp, as well as deformation monitoring of walls, were used in order to review geotechnical design parameters that represent the full-scale behavior of the ground. Additional nails and soldier piles together with building mat foundation were implemented as a complementary lateral support in the retaining system. From an engineering point of view, by assuming a corrosion rate of 0.065 mm/a for existent rebars, according to chemical and electrical resistivity tests, the long-term performance of the revised retaining system was verified by static and pseudo-dynamic ultimate limit state analyses. Performance monitoring during the construction shows that the measured deformation is in the lower limit of the prediction.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): 〈/p〉

Beschreibung: 〈p〉Publication date: Available online 6 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Nick Barton, Eda Quadros〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Pre-grouting ahead of tunnels has three main functions: to control water inflow into the tunnel, to limit groundwater drawdown above the tunnel, and to make tunnelling progress more predictable since rock mass quality is effectively improved. It helps to avoid settlement damage caused by consolidation of clay deposits beneath built-up areas, since towns tend to be built where terrain is more flat, due to the clay deposits. There are so many instances of settlement damage that the profession needs to take note of the need for high-pressure pre-grouting, to use micro-cements and micro-silica additives. The use of high-pressure injection may cause joint jacking, but this is local in extent when the rapid pressure decay away from an injection hole is understood. This effect is variable and depends on the geometrical parameters of the joints. This pressure-decay advantage must not be violated by maintaining high pressure when grout flow from the injection hole has ceased. The latter can cause damage to the grouting already achieved. Simplified methods of estimating mean hydraulic apertures (〈em〉e〈/em〉) from Lugeon testing are described, and from more sophisticated three-dimensional (3D) permeability measurement. The estimation of the larger mean physical joint apertures (〈em〉E〈/em〉) is based on the joint roughness coefficient (JRC). Comparison is then made with the empirical aperture-particle size criterion 〈em〉E〈/em〉 〉 4〈em〉d〈/em〉〈sub〉95〈/sub〉, where 〈em〉d〈/em〉〈sub〉95〈/sub〉 represents almost the largest cement particle size. Depending on joint set orientations and on the available micro-cements, the decision must be made of which range of pre-injection pressure should be aimed for, using successive reductions of the water-cement ratio 〈em〉w〈/em〉/〈em〉c〈/em〉. More simple estimation of permeability, also with depth dependence, can be made with the empirical link between the rock mass quality 〈em〉Q〈/em〉 and permeability, which is termed 〈em〉Q〈/em〉〈sub〉H2O〈/sub〉. The value of this parameter can be based on core-logging or in-tunnel face logging. The 3D before-and-after-grouting permeability measurements have been used to justify the quantification of rock mass quality 〈em〉Q〈/em〉-parameter improvement, and the consequent increases in expected P-wave velocity and deformation modulus, for application in dam foundation treatment and its monitoring.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 6 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Luis-Fernando Contreras, Edwin T. Brown〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A Bayesian approach is proposed for the inference of the geotechnical parameters used in slope design. The methodology involves the construction of posterior probability distributions that combine prior information on the parameter values with typical data from laboratory tests and site investigations used in design. The posterior distributions are often complex, multidimensional functions whose analysis requires the use of Markov chain Monte Carlo (MCMC) methods. These procedures are used to draw representative samples of the parameters investigated, providing information on their best estimate values, variability and correlations. The paper describes the methodology to define the posterior distributions of the input parameters for slope design and the use of these results for evaluation of the reliability of a slope with the first order reliability method (FORM). The reliability analysis corresponds to a forward stability analysis of the slope where the factor of safety (FS) is calculated with a surrogate model from the more likely values of the input parameters. The Bayesian model is also used to update the estimation of the input parameters based on the back analysis of slope failure. In this case, the condition 〈em〉FS〈/em〉 = 1 is treated as a data point that is compared with the model prediction of FS. The analysis requires a sufficient number of observations of failure to outbalance the effect of the initial input parameters. The parameters are updated according to their uncertainty, which is determined by the amount of data supporting them. The methodology is illustrated with an example of a rock slope characterised with a Hoek-Brown rock mass strength. The example is used to highlight the advantages of using Bayesian methods for the slope reliability analysis and to show the effects of data support on the results of the updating process from back analysis of failure.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Jielin Li, Rennie B. Kaunda, Shrey Arora, Philipp Hartlieb, Priscilla P. Nelson〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Fully-coupled thermo-mechanical simulations are implemented in COMSOL Multiphysics to investigate micro-scale stress-strain variability in pegmatite specimens subjected to thermal loading using microwaves. Thermally-induced compressive and tensile stresses increase as the microwave irradiation duration increases. The dielectric constant, coefficient of expansion, and type and size of mineralogical boundary have significant impacts on the responses of the rock to microwave irradiation. The maximum principal stress of the chlorite is the smallest, indicating that the chlorite experiences the most damage under microwave irradiation, followed by the quartz. The maximum principal stress values of plagioclase and orthoclase are larger, indicating that they are likely to incur the least damage. Where quartz or chlorite is dominant, the resulting von Mises stresses are consistently higher after 120 s of microwave irradiation. The rate of generation of von Mises stresses increases most rapidly along the interface between quartz and plagioclase, and the interface between quartz and orthoclase, followed by the interface between quartz and chlorite, and finally the interface between plagioclase and orthoclase. The presented modeling approach provides a practical method to investigate stress-strain relationships within mineralogical boundaries inside a rock thin section.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 30 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Zhenghong Huang, Shouchun Deng, Haibo Li, Hong Zuo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, a compression-to-tension conversion technique is developed by applying predominant mode I loading test, using a servo-controlled compression system. The technique is applied to thin mortar plate specimens of different widths that include a prefabricated crack on either a single side to facilitate unilateral crack propagation, or prefabricated cracks positioned on both sides asymmetrically with respect to the specimen midpoint to facilitate bilateral crack propagation under direct tensile stress with a loading rate of 0.001 mm/s. The results show that the main pathways of unilateral crack propagation governing specimen failure are fluctuated locally, but present an approximately straight line overall in the absence of pre-existing internal defects. However, the pathways of bilateral crack propagation are relatively complex, although they present similar characteristics. Analysis results suggest that bilateral crack propagation can be basically divided into three stages, i.e. a stage of linear propagation, a stage representing deviation from the other crack, and a stage where one crack approaches either the other crack or approaches the opposite edge of the specimen, and thereby forming a continuous crack through the specimen. In addition, the stress-strain curves of bilateral crack specimens do not vary significantly around the point of peak stress prior to specimen failure, which means that the specimens do not fail instantaneously.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 31 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Harry Holmes, Emilio Garcia-Taengua, Raul Fuentes〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper presents a rigorous statistical approach to identify the controlling factors in the development of ground movements associated with deep excavations. It also gives the most suitable definition of support stiffness from many suggested definitions in the literature. The study is based on a newly compiled database from 389 case studies of propped and anchored excavations. Data mining techniques (e.g. principal component analysis and multi-linear regression) were used to identify significant relationships between the parameters under study and to quantify the global trends in the database. The study shows that the main factors controlling the ground movements are those related to ground conditions, confirming the conclusions of previous empirical studies. It is also shown that the definition of Addenbrooke et al. (1994) is the most suitable expression of support stiffness, therefore providing conclusive evidence for its future use.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 22 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Liansheng Tang, Zhanlun Zhao, Zhengui Luo, Yinlei Sun〈/p〉 〈div xml:lang="en"〉 〈h5〉A b s t r a c t〈/h5〉 〈div〉〈p〉The traditional limit equilibrium method (LEM) is often used to search for the failure surface with a minimum safety factor of slope. In this method, the failure surface is considered as a shear surface, irrespective of its form. However, tensile cracks are frequently found at the outcrops of landslides. In this study, three sets of tests on small-scale landslides with different inclination angles were conducted. The test results demonstrated that tensile cracks could arise in the slope sliding process and the failure surface is composed of both a shear and a tensile fracture surface. Based on the test results, we used the improved LEM, and replaced the traditional shear failure surface by a tensile-shear coupling one, thus new tensile failure modes for slope stability analysis can be established. The safety factors of slope in different failure modes were compared, which show that when considering soil tensile failure and tensile strength less than a certain value (e.g. 15 kPa, 44 kPa and 55 kPa for linear, circular and logarithmic spiral failure surfaces, respectively), the safety factors of slope with three different failure surfaces are less than the one that did not consider the tensile failure. The most critical failure surfaces of the slope may be composed of shear and tensile damages because the tensile strength of the soil cannot be generally greater than its cohesion.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 10, Issue 6〈/p〉 〈p〉Author(s): Dinesh R. Katti, Keshab B. Thapa, Kalpana S. Katti〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Swelling clays are found extensively in various parts of the world, and sodium-montmorillonite (Na-MMT) is the main constituent of an expansive clay mineral. In this work, the swelling behavior of Na-MMT clay with a wide range of organic fluids, high polar through low polar fluids, is studied using a combination of Fourier transform infrared (FTIR) technique and molecular dynamics (MD) simulations. The construction of the representative clay–fluid models is carried out, and the nature of nonbonded interactions between clay and fluids is studied using MD. Our FTIR and MD simulations results suggest the significant nonbonded interactions between Na-MMT clay and polar fluids, such as formamide and water. The nonbonded interactions of Na-MMT with methanol and acetone are significantly less than those in Na-MMT with polar fluids. The interactions of the fluids with various entities of the clay such as Si〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉O, Fe〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉OH, Mg〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉OH, and Al〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉OH captured via the spectroscopy experiments and modeling provide a finer understanding of the interactions and their contributions to swelling. The MD simulations are able to capture the band shifts observed in the spectra obtained in the spectroscopy experiments. This work also captures the conformations of interlayer sodium ions with formamide, water, methanol, and acetone during swelling. These nonbonded interactions provide insight into the molecular mechanism that the polarity of fluids plays an important role in the initiation of interlayer swelling, alteration in the orientations, and evolution of microstructure of swelling clays at the molecular scale.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Daisuke Katsuki, Marte Gutierrez, Abdulhadi Almrabat〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉It is well known that shear wave propagates slower across than parallel to a fracture, and as a result, a travelling shear wave splits into two directions when it encounters a fracture. Shear wave splitting and permeability of porous rock core samples having single fracture were experimentally investigated using a high-pressure triaxial cell, which can measure seismic shear wave velocities in two directions mutually perpendicular to the sample axis in addition to the longitudinal compressive wave velocity. A single fracture was created in the samples using a modified Brazilian split test device, where the cylindrical sample edges were loaded on two diametrically opposite lines by sharp guillotines along the sample length. Based on tilt tests and fracture surface profilometry, the method of artificially induced tensile fracture in the sample was found to create repeatable fracture surfaces and morphologies. Seismic velocities of the fractured samples were determined under different levels of stress confinement and fracture shear displacement or mismatch. The effective confining stress was varied from 0.5 MPa to 55 MPa, while the fractures were mismatched by 0 mm, 0.45 mm and 1 mm. The degree of matching of the fracture surfaces in the core samples was evaluated using the joint matching coefficient (〈em〉JMC〈/em〉). Shear wave splitting, as measured by the difference in the magnitudes of shear wave velocities parallel (〈em〉V〈/em〉〈sub〉S1〈/sub〉) and perpendicular (〈em〉V〈/em〉〈sub〉S2〈/sub〉) to the fracture, is found to be insensitive to the degree of mismatching of the fracture joint surfaces at 2 MPa, and decreased and approached zero as the effective stress was increased. Simple models for the stress- and 〈em〉JMC-〈/em〉dependent shear wave splitting and fractured rock permeability were developed based on the experimental observations. The effects of the joint wall compressive strength (〈em〉JCS〈/em〉), 〈em〉JMC〈/em〉 and stress on the stress dependency of joint aperture were discussed in terms of hydro-mechanical response. Finally, a useful relationship between fractured rock permeability and shear wave splitting was found after normalization by using 〈em〉JMC〈/em〉.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Sankhaneel Sinha, Gabriel Walton〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉With recent advances in numerical modeling, design of underground structures increasingly relies on numerical modeling-based analysis approaches. While modeling tools like the discrete element method (DEM) and the combined finite-discrete element method (FDEM) are useful for investigating small-scale damage processes, continuum models remain the primary practical tool for most field-scale problems. The results obtained from such models are significantly dependent on the selection of an appropriate yield criterion and dilation angle. Towards improving its capabilities in handling mining-related problems, the authors have previously developed a new yield criterion (called progressive S-shaped criterion). The focus of the current study is to demonstrate its use in modeling rock pillars through a comparative analysis against four other yield criteria. In addition to the progressive S-shaped criterion, only one out of the four other criteria predicted a trend in strength consistent with an empirical pillar strength database compiled from the literature. Given the closely-knit relationship between yield criteria and dilation angle in controlling the overall damage process, a separate comparison was conducted using a mobilized dilation model, a zero degree dilation angle and a constant non-zero dilation angle. This study also investigates the impact of meso-scale heterogeneity in mechanical properties on the overall model response by assigning probability distributions to the input parameters. The comparisons revealed that an isotropic model using a combination of progressive S-shaped criterion and mobilized dilation angle model is sufficient in capturing the behaviors of rock pillars. Subsequently, the pillar model was used to assess the effect of 〈em〉L〈/em〉/〈em〉W〈/em〉 (length/width) ratio on the peak strength.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Yaru Lv, Jiagui Liu, Ziming Xiong〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Calcareous sand has distinct characteristics in comparison with silica sand, such as dynamic behavior at high strain rates (HSRs). This is closely related to pile driving, aircraft wheel loading and mining activities. To understand the response of calcareous sand at HSRs, a series of dynamic tests is performed using the split Hopkinson pressure bar (SHPB) with steel sleeve, including 6 validation tests of bar-against-bar and 16 comparative tests relevant to the relative density and strain rate of calcareous and silica sands. The apparent dynamic stiffness of calcareous sand is approximately 10% of that for silica sand due to different particle shapes and mineral compositions. The axial stress-strain response of silica sand is mainly governed by the deformation of individual grain and soil skeleton, and particle crushing. However, porous calcareous sand shows yielding and strain-hardening responses that are always followed by particle crushing. As the applied loading increases, the particle crushing of calcareous sand develops from local instability to whole breakage. Calcareous sand has lower viscous flow effects compared with silica sand at HSRs.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Hossein Agheshlui, Mohammad H. Sedaghat, Siroos Azizmohammadi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study compares the calculated fracture apertures in a fragmented rock layer under different stress scenarios using two different approaches. Approach 1 is a simplified method using a two-dimensional (2D) mapping of the fracture network and projects the far-field stresses to individual fractures, and calculates the dilation, normal and shear displacements using experimental stiffnesses available in the literature. Approach 2 employs a three-dimensional (3D) finite element method (FEM) for the mechanical analysis of the fragmented rock layer considering the interaction with the neighbouring rock layers, frictional interfaces between the rock blocks, stress variations within the fragmented rock layer, and displacements, rotations and deformations of rock blocks. After calculating the fracture apertures using either of the approaches, the permeability of the fragmented rock layer is calculated by running flow simulations using the updated fracture apertures. The comparison between the results demonstrates an example of the inaccuracies that may exist in methods that use simplified assumptions such as 2D modelling, ignoring the block rotations and displacements, projected far-field stresses on fractures, and the stress variations within the rock layer. It is found that for the cases considered here, the permeability results based on apertures obtained from the simplified approach could be 40 times different from the results from apertures calculated using a full mechanical approach. Hence, 3D mechanical modelling implementing realistic boundary conditions, while considering the displacements and rotations of rock blocks, is suggested for the calculation of apertures in fragmented rocks.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 30 May 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Liang Xu, Qi Li, Matthew Myers, Quan Chen, Xiaochun Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Carbon capture, utilization and storage (CCUS) is considered as a very important technology for mitigating global climate change. Carbon dioxide (CO〈sub〉2〈/sub〉) injected into an underground reservoir will induce changes in its physical properties and the migration of CO〈sub〉2〈/sub〉 will be affected by many factors. Accurately understanding these changes and migration characteristics of CO〈sub〉2〈/sub〉 is crucial for selecting a CCUS project site, estimating storage capacity and ensuring storage security. In this paper, the basic principles of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) technologies are briefly introduced in the context of laboratory experiments related to CCUS. The types of NMR apparatus, experimental samples and testing approaches applied worldwide are discussed and analyzed. Then two typical NMR core analysis systems used in CCUS field and a self-developed high-pressure, low-field NMR rock core flooding experimental system are compared. Finally, a summary of the current deficiencies related to NMR applied to CCUS field is given and future research plans are proposed.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 22 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Andrey Polyakov, Aleksandr Zhabin, Eugene Averin, Aleksey Polyakov〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉One of the promising methods for rock cutting technology is the use of high-speed water jets. In order to improve the cutting capacity of water jets without increasing the hydraulic power of equipment, pulsed water jets are basically used to increase the rock cutting efficiency. However, there are no mature recommendations for selection of rational parameters, and the relationship between indicators of rock cutting efficiency and parameters of pulsed water jet is still not established. In this context, we aimed at developing a generalized equation for calculating rock cutting efficiency, in which all the major parameters in consideration of rock cutting process are included. Then, a calibration of the rational parameters of rock cutting by pulsed water jets was conducted. The results are likely helpful for increasing productivity and reducing energy consumption.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Hemant Agrawal, A.K. Mishra〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The blast-induced ground vibration prediction using scaled distance regression analysis is one of the most popular methods employed by engineers for many decades. It uses the maximum charge per delay and distance of monitoring as the major factors for predicting the peak particle velocity (PPV). It is established that the PPV is caused by the maximum charge per delay which varies with the distance of monitoring and site geology. While conducting a production blasting, the waves induced by blasting of different holes interfere destructively with each other, which may result in higher PPV than the predicted value with scaled distance regression analysis. This phenomenon of interference/superimposition of waves is not considered while using scaled distance regression analysis. In this paper, an attempt has been made to compare the predicted values of blast-induced ground vibration using multi-hole trial blasting with single-hole blasting in an opencast coal mine under the same geological condition. Further, the modified prediction equation for the multi-hole trial blasting was obtained using single-hole regression analysis. The error between predicted and actual values of multi-hole blast-induced ground vibration was found to be reduced by 8.5%.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 13 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Hai-Sui Yu, Pei-Zhi Zhuang, Pin-Qiang Mo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper is prepared in honour of Professor E.T. Brown for his outstanding contributions to rock mechanics and geotechnical engineering and also for his personal influence on the first author's research career in geomechanics and geotechnical engineering. As a result, we have picked a topic that reflects two key research areas in which Professor E.T. Brown has made seminal contributions over a long and distinguished career. These two areas are concerned with the application of the critical state concept to modelling geomaterials and the analysis of underground excavation or tunnelling in geomaterials. Partially due to Professor Brown's influence, the first author has also been conducting research in these two areas over many years. In particular, this paper aims to describe briefly the development of a unified critical state model for geomaterials together with an application to cavity contraction problems and tunnelling in soils.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Wangping Qian, Taiyue Qi, Yunjian Zhao, Yizhou Le, Haiyang Yi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Stratum deformation (settlement) is a challenging issue in tunnel engineering, especially when construction of metro tunnels has to undercut high-speed railway. For this purpose, we used the FLAC〈sup〉3D〈/sup〉 software to analyze the stratum settlement characteristics of high-speed railway at different crossing angles intersected by metro tunnel, in terms of ground settlement trough, stratum slip line and irregularity of ballastless tracks. According to the evolution of the stratum settlement at different angle regions, an optimized angle is proposed for the actual project design. In order to reduce the influence of stratum settlement on the safety of high-speed railway, an approach of safety assessment is proposed for the shield engineering undercutting high-speed railway, as per Chinese specifications using numerical results and on-site conditions. A case study is conducted for the shield tunnel section crossing the Wuhan – Guangzhou High-speed Railway between the Guangzhou North Railway Station and the Huacheng Road Station, which represents the first metro tunnel project passing below a high-speed railway in China. A series of measures is taken to ensure the safe excavation of the shield tunnel and the operation of the high-speed railway. The results can provide a technical support for performing a safety evaluation between high-speed railways and metro tunnels.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): A.K. Verma, Sahil Sardana, Pushpendra Sharma, Lal Dinpuia, T.N. Singh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Rockfall is one of severe natural hazards that are frequently reported in northeast region of India. It carries rock block falling from the cliff with high velocities and energies which can result in damages to vehicles, disruption to transportation, injuries and fatalities. The massive rockfall event which occurred in April 2017 on the highway NH-44A, near Lengpui Airport, blocked the traffic for 1 d, and fortunately, no casualties were reported as the event occurred in the night. This is the only highway connecting the Aizawl city to the airport and the region is highly prone to rockfall events. Hence assessment of rockfall along this highway is necessary. In the current study, rockfall hazard assessment has been carried out on three locations by rockfall hazard rating system (RHRS). During pre-failure analysis, the result shows that most hazardous slopes have RHRS score of 639. The slopes were found to be vulnerable and later on the rockfall activity occurred. Three-dimensional (3D) stability analysis has been carried out using 3DEC software package to analyze the failure behavior and to decide the rockfall-prone zone (unstable blocks) for slope. The total displacement of 2.24 cm and velocity of 2.25 mm/s of the failed block have been observed in the numerical analysis. Further, the rockfall vulnerable zone (unstable blocks) is considered to determine the parameters such as run-out distance, bounce height and energies of the falling rock blocks. The maximum total kinetic energy of 5047 kJ has been observed in the numerical analysis with the maximum run-out distance up to 18 m.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Partha Narayan Mishra, Alexander Scheuermann, Thierry Bore, Ling Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Fine-grained clayey soils are prone to substantial volume changes during desiccation in response to the dynamics of their moisture regime, and are of critical importance in several geotechnical and geo- environmental engineering applications. As such, the complex interactions between the fraction of soil solids and the ionic pore fluid play a critical role in governing such volume changes, and have been the focus in studies dealing with marine geotechnology, mine-tailing ponds, engineered barrier systems, etc. With this in mind, the present investigation evaluates the volume changes and accompanying densification from a saturated slurry state to a constant volume state of a reference fine-grained geomaterial, kaolin, subjected to evaporative dewatering. For this purpose, several parametric studies involving determination of soil shrinkage characteristic curves (SSCCs) of kaolin under the influence of varied salt constituents and concentrations of pore fluid are performed. Furthermore, a critical assessment of SSCCs depicting progressive shrinkage and volume change behaviour of geomaterials is provided, followed by the analysis of experimentally obtained SSCCs of the kaolin to explore the impacts of pore fluid salinity. Moreover, the SSCCs are parameterised with a predictive model and the fitting parameters are used to quantitatively demonstrate the salinity-dependent volume change response of a representative fine-grained porous system.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Ngoc Anh Do, Daniel Dias, Van Diep Dinh, Tien Tung Tran, Van Canh Dao, Viet Doan Dao, Phuc Nhan Nguyen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The amount of tunnels excavated along stratified/sedimentary rock masses in Quangninh coal mine area, Vietnam, is gradually increasing. Rock mass in Quangninh is characterized by beddings between rock layers. The behavior of stratified rock masses surrounding the tunnels depends on both the intact rock and the beddings between rock layers. The main characteristics of stratified rock masses that need to be considered are their heterogeneity and anisotropy. Depending on the dip angle of rock layers, movements and failure zones developed surrounding the tunnels can be asymmetrical over the vertical axis of tunnel. This asymmetry causes adverse behaviors of the tunnel structures. The objective of this study is to highlight convergences and yielded zones developed in rock masses surrounding noncircular tunnels in Quangninh coal mine area using a finite element method. The presence of bedding joints is explicitly simulated. The numerical results indicated that with the increase in dip angle of bedding joints, the stress asymmetry over the tunnel vertical axis increases. It gradually leads to an asymmetry of the failure zone surrounding the tunnel. An increase of rock mass quality means a decrease of rock mass sensitivity to the discontinuities. In addition, a dip angle of the bedding joints of approximately 45° could be considered as the critical angle at which the rock mass mechanism changes between sliding and bending.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Amin Soltani, Mehdi Mirzababaei〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The present discussion aims at complementing the original work published by Baldovino et al. (2018) by outlining a novel point of view. In light of the inherent limitations associated with the empirical model suggested in the original article, the dimensional analysis technique was introduced to the soil-lime strength problem, thereby leading to the development of simple and physically meaningful dimensional models capable of predicting the unconfined compressive and splitting tensile strengths of compacted soil-lime mixtures as a function of the mixture's index properties, i.e. lime content, initial placement (or compaction) condition, initial specific surface area and curing time. The predictive capacity of the proposed dimensional models was examined and validated by statistical techniques. The proposed dimensional models contain a limited number of fitting parameters, which can be calibrated by minimal experimental effort and hence implemented for predictive purposes.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 2 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Yifei Sun, Sanjay Nimbalkar, Chen Chen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Particle breakage is commonly observed in granular materials when subjected to external loads. It was found that particle breakage would occur during both sample preparation and loading stages. However, main attention was usually paid to the particle breakage behaviour of samples during loading stage. This study attempts to explore the breakage behaviour of granular materials during sample preparation. Triaxial samples of rockfill aggregates are prepared by layered compaction method to achieve different relative densities. Extents of particle breakage based on the gradings before and after test are presented and analysed. It is found that particle breakage during sample preparation cannot be ignored. Gradings after test are observed to shift away from the initial grading. Aggregates with larger size that appear to break are more than the smaller-sized ones. Irrespective of the initial gradings, an increase in the extent of particle breakage with the increasing relative density is observed during sample preparation.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 2 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Tongtao Wang, Jianjun Li, Gang Jing, Qingqing Zhang, Chunhe Yang, J.J.K. Daemen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Increasing the allowable gas pressure of underground gas storage (UGS) is one of the most effective methods to increase its working gas capacity. In this context, hydraulic fracturing tests are implemented on the target formation for the UGS construction of Jintan salt caverns, China, in order to obtain the minimum principal in situ stress and the fracture breakdown pressure. Based on the test results, the maximum allowable gas pressure of the Jintan UGS salt cavern is calibrated. To determine the maximum allowable gas pressure, KING-1 and KING-2 caverns are used as examples. A three-dimensional (3D) geomechanical model is established based on the sonar data of the two caverns with respect to the features of the target formation. New criteria for evaluating gas penetration failure and gas seepage are proposed. Results show that the maximum allowable gas pressure of the Jintan UGS salt cavern can be increased from 17 MPa to 18 MPa (i.e. a gradient of about 18 kPa/m at the casing shoe depth). Based on numerical results, a field test with increasing maximum gas pressure to 18 MPa has been carried out in KING-1 cavern. Microseismic monitoring has been conducted during the test to evaluate the safety of the rock mass around the cavern. Field monitoring data show that KING-1 cavern is safe globally when the maximum gas pressure is increased from 17 MPa to 18 MPa. This shows that the geomechanical model and criteria proposed in this context for evaluating the maximum allowable gas pressure are reliable.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 27 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): R.P. Bewick, P.K. Kaiser, F. Amann〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Hoek-Brown (HB) failure criterion and the geological strength index (GSI) were developed for the estimation of rock mass strength in jointed and blocky ground where rock mass failure is dominated by sliding along open joints and rotation of rock blocks. In massive, veined and moderately jointed rock in which rock blocks cannot form without failure of intact rock, the approach to obtain HB parameters must be modified. Typical situations when these modifications are required include the design of pillars, excavation and cavern stability, strainburst potential assessment, and tunnel support in deep underground conditions (around 〈em〉σ〈/em〉〈sub〉1〈/sub〉/〈em〉σ〈/em〉〈sub〉ci〈/sub〉 〉 0.15, where 〈em〉σ〈/em〉〈sub〉1〈/sub〉 is the major principal compressive stress and 〈em〉σ〈/em〉〈sub〉ci〈/sub〉 is the unconfined compressive strength of the homogeneous rock) in hard brittle rocks with 〈em〉GSI〈/em〉 ≥ 65. In this article, the strength of massive to moderately jointed hard rock masses is investigated, and an approach is presented to estimate the rock mass strength envelope using laboratory data from uniaxial and triaxial compressive strength tests without reliance on the HB-GSI equations. The data from tests on specimens obtained from massive to moderately jointed heterogeneous (veined) rock masses are used to obtain the rock and rock mass strengths at confining stress ranges that are relevant for deep tunnelling and mining; and a methodology is presented for this purpose from laboratory data alone. By directly obtaining the equivalent HB rock mass strength envelope for massive to moderately jointed rock from laboratory tests, the HB-GSI rock mass strength estimation approach is complemented for conditions where the GSI-equations are not applicable. Guidance is also provided on how to apply the proposed approach when laboratory test data are not or not yet available.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 21 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Marzieh Khalili, Abdul Vahed Mirzakurdeh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The faults and fractures are known as two of the most important parameters in earthquake occurrence. During the construction in urban areas, faults and fractures may be covered in depth and thus are not visible at the ground surface. In this context, non-invasive geophysical prospecting methods (microtremor and geoelectrical methods) and borehole data were used to detect subsurface geological structures (hidden faults) in a suburb of Shiraz in Iran. The horizontal to vertical spectral ratio (HVSR) method was used to obtain the dynamic parameters (predominant frequency and resonance amplitude) of the soil, to detect hidden faults. The results show that the abrupt changes in the sediment thickness and predominant frequencies at a specific direction (NW-SE) can be related to the displacement of a nearly vertical fault with NW-SE trend. In addition, the electrical resistivity method using continuous resistivity profiling (CRP) and Schlumberger arrays was employed to detect a hidden fault and the results were compared with previous data. The obtained results of both arrays illustrate the presence of a nearly vertical fault with NW-SE trend in the region. Comparison of all results shows that the detected faults by both methods are consistent with each other. Therefore, it can be conclusive that combination of the two methods is a useful and reliable approach to study and detect hidden faults.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 21 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Iman Hosseinpour, Cristian Soriano, Marcio S.S. Almeida〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper describes a three-dimensional (3D) numerical analysis of a test embankment on geotextile-encased columns (GECs), in comparison with two-dimensional (2D) axisymmetric and plane strain analyses. The 3D numerical analysis was performed considering a rectangular strip under the embankment centerline. The 2D analysis was also carried out using axisymmetric unit cell and plane strain approaches. Numerical results indicated that the adopted 3D strip model represented well the measured deformations and pore pressure evolution during embankment construction and post-contraction periods. Unlike the unit cell model, both plane strain and 3D analyses could properly determine the settlement profile along the embankment base as well as the profile of the horizontal soil deformation beneath the embankment toes. The plane strain analysis, however, was not able to compute the geotextile ring force which might be simply calculated using the axisymmetric unit cell approach. The paper also showed that, due to horizontal boundary fixities applied to the embankment borders, the unit cell model clearly underestimated the tension developed in the basal geogrid.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 11 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Chijioke Christopher Ikeagwuani, Donald Chimobi Nwonu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Expansive soils are problematic due to the performances of their clay mineral constituent, which makes them exhibit the shrink-swell characteristics. The shrink-swell behaviours make expansive soils inappropriate for direct engineering application in their natural form. In an attempt to make them more feasible for construction purposes, numerous materials and techniques have been used to stabilise the soil. In this study, the additives and techniques applied for stabilising expansive soils will be focused on, with respect to their efficiency in improving the engineering properties of the soils. Then we discussed the microstructural interaction, chemical process, economic implication, nanotechnology application, as well as waste reuse and sustainability. Some issues regarding the effective application of the emerging trends in expansive soil stabilisation were presented with three categories, namely geoenvironmental, standardisation and optimisation issues. Techniques like predictive modelling and exploring methods such as reliability-based design optimisation, response surface methodology, dimensional analysis, and artificial intelligence technology were also proposed in order to ensure that expansive soil stabilisation is efficient.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Zhaohuang Zhang, Muhammad Aqeel, Cong Li, Fei Sun〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Predicting the cutter consumption and the exact time to replace the worn-out cutters in tunneling projects constructed with tunnel boring machine (TBM) is always a challenging issue. In this paper, we focus on the analyses of cutter motion in the rock breaking process and trajectory of rock breaking point on the cutter edge in rocks. The analytical expressions of the length of face along which the breaking point moves and the length of spiral trajectory of the maximum penetration point are derived. Through observation of rock breaking process of disc cutters as well as analysis of disc rock interaction, the following concepts are proposed: the arc length theory of predicting wear extent of inner and center cutters, and the spiral theory of predicting wear extent of gage and transition cutters. Data obtained from 5621 m-long Qinling tunnel reveal that among 39 disc cutters, the relative errors between cumulatively predicted and measured wear values for nine cutters are larger than 20%, while approximately 76.9% of total cutters have the relative errors less than 20%. The proposed method could offer a new attempt to predict the disc cutter's wear extent and changing time.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Maria Heloisa Barros de Oliveira Frascá〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉All engineering projects consist of several steps, and one of the main tasks is to identify and characterize the most important features of rock types that will be excavated, crushed, or mined for any particular usage purpose, from a single residential building to major works of infrastructure. Laboratory investigation on engineering geology is thus conducted in order to determine the most relevant rock properties when designing structures such as mining shafts, tunnels, buildings, or reservoir dams to be built in sites associated with rocks. A wide range of laboratory tests is available, making the correct choice of test methods greatly relevant to determine the key property for the planned use of the rock. This paper is an illustrative case of laboratory testing of basaltic rocks to be used as riprap in a reservoir dam. It shows the important role of the petrographic study carried out to analyze the distribution pattern of smectite clay minerals. Test results are explained for the assessment of rock alterability, an essential aspect for the selection of the most suitable basalt variety for the envisaged conditions of use.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Jiliang Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉One of the important issues for geotechnical engineers is the characterization of soil properties such as cohesion and internal friction angle by means of soil testing. A new experimental method of soil characterization based on the surface displacement of strip loaded soils is proposed. The theory to relate the soil deformation/displacement to soil strength properties is presented and compared with a series of conventional soil characterization techniques with direct shear tests. The proposed/developed strip loading tests provide reasonably accurate results compared with traditional direct shear tests. The new strip loading physical simulation and testing devices are helpful for understanding soil strength concepts and also provide an effective bridge connecting with engineering mechanics and foundation engineering courses instructions wherein derivation of bearing capacity theory equations is based on the same Mohr-Coulomb soil strength parameters. The advantages, limitations, and use of the strip loading modeling/testing technique in engineering education and further more in depth researches are discussed in the concluding remarks part.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 1〈/p〉 〈p〉Author(s): Shaosen Ma, Weizhong Chen, Wusheng Zhao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Foamed concrete has a good energy absorption capability and can be used as seismic isolation material for tunnels. This study aims to investigate the mechanical properties and associated seismic isolation effects of foamed concrete layer in rock tunnel. For this, a series of uniaxial/triaxial compression tests was conducted to understand the effects of concrete density, confining stress and strain rate on the mechanical properties of foamed concrete. The direct shear tests were also performed to investigate the effects of concrete density and normal stress on the nonlinear behaviors of foamed concrete layer-lining interface. The test results showed that the mechanical properties of foamed concrete are significantly influenced by the concrete density. The foamed concrete also has high volumetric compressibility and strain-rate dependence. The peak stress, residual stress, shear stiffness and residual friction coefficient of the foamed concrete layer-lining interface are influenced by the foamed concrete density and normal stress applied. Then, a crushable foam constitutive model was constructed using ABAQUS software and a composite exponential model was also established to study the relationship between shear stress and shear displacement of the interface, in which their parameters were fitted based on the experimental results. Finally, a parametric analysis using the finite element method (FEM) was conducted to understand the influence of foamed concrete layer properties on the seismic isolation effect, including the density and thickness of the layer as well as the shear stiffness and residual friction coefficient of the interface. It was revealed that lower density and greater thickness in addition to smaller shear stiffness or residual friction coefficient of the foamed concrete layer could yield better seismic isolation effect, and the influences of the first two tend to be more significant.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 14 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Dongdong Xu, Aiqing Wu, Cong Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The numerical manifold method (NMM) can be viewed as an inherent continuous-discontinuous numerical method, which is based on two cover systems including mathematical and physical covers. Higher-order NMM that adopts higher-order polynomials as its local approximations generally shows higher precision than zero-order NMM whose local approximations are constants. Therefore, higher-order NMM will be an excellent choice for crack propagation problem which requires higher stress accuracy. In addition, it is crucial to improve the stress accuracy around the crack tip for determining the direction of crack growth according to the maximum circumferential stress criterion in fracture mechanics. Thus, some other enriched local approximations are introduced to model the stress singularity at the crack tip. Generally, higher-order NMM, especially first-order NMM wherein local approximations are first-order polynomials, has the linear dependence problems as other partition of unit (PUM) based numerical methods does. To overcome this problem, an extended NMM is developed based on a new local approximation derived from the triangular plate element in the finite element method (FEM), which has no linear dependence issue. Meanwhile, the stresses at the nodes of mathematical mesh (the nodal stresses in FEM) are continuous and the degrees of freedom defined on the physical patches are physically meaningful. Next, the extended NMM is employed to solve multiple crack propagation problems. It shows that the fracture mechanics requirement and mechanical equilibrium can be satisfied by the trial-and-error method and the adjustment of the load multiplier in the process of crack propagation. Four numerical examples are illustrated to verify the feasibility of the proposed extended NMM. The numerical examples indicate that the crack growths simulated by the extended NMM are in good accordance with the reference solutions. Thus the effectiveness and correctness of the developed NMM have been validated.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 24 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): G. Li, X.F. Cheng, H. Pu, C.A. Tang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Damage smear method (DSM) is adopted to study trans-scale progressive rock failure process, based on statistical meso-damage model and finite element solver. The statistical approach is utilized to reflect the mesoscopic rock heterogeneity. The constitutive law of representative volume element (RVE) is established according to continuum damage mechanics in which double-damage criterion is considered. The damage evolution and accumulation of RVEs are used to reveal the macroscopic rock failure characteristics. Each single RVE will be represented by one unique element. The initiation, propagation and coalescence of meso-to macro-cracks are captured by smearing failed elements. The above ideas are formulated into the framework of the DSM and programed into self-developed rock failure process analysis (RFPA) software. Two laboratory-scale examples are conducted and the well-known engineering-scale tests, i.e. Atomic Energy of Canada Limited’s (AECL’s) Underground Research Laboratory (URL) tests, are used for verification. It shows that the simulation results match with other experimental results and field observations.〈/p〉 〈p〉© 2019 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (〈a href="https://creativecommons.org/licenses/by-nc-nd/4.0/" target="_blank"〉http://creativecommons.org/licenses/by-nc-nd/4.0/〈/a〉).〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 14 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Eleni Stavropoulou, Matthieu Briffaut, Frédéric Dufour, Guillaume Camps〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In the context of the Cigéo project, the French National Radioactive Waste Management Agency (Andra) is studying the behaviour of a deep geological facility for radioactive waste deposit in the Callovo-Oxfordian (COx) claystone. The assessment of durability of this project requires the prediction of irreversible strain over a large time scale. The mechanical interaction of the host rock and the concrete support of tunnels must be investigated to ensure the long-term sustainability of the structure. The instantaneous and time-dependent behaviour of the claystone-concrete interface is experimentally investigated with direct shear tests and long-duration shear tests of a few months. The mechanical and structural state of the claystone which is affected after interaction with concrete reflects to the response of the claystone-concrete interface, and thus different types of COx claystone-concrete interfaces are tested. The delayed deformation of the interface is found to be linked to the level of the normal loading and the loading history, while a different response of the interface was observed from the short- and long-duration tests, indicating a possible progressive modification of interface under long-duration loadings.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 14 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Richeng Liu, Ming He, Na Huang, Yujing Jiang, Liyuan Yu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study proposes a double-rough-walled fracture model to represent the natural geometries of rough fractures. The rough surface is generated using a modified successive random additions (SRA) algorithm and the aperture distribution during shearing is calculated using a mechanistic model. The shear-flow simulations are performed by directly solving the Navier-Stokes (NS) equations. The results show that the double-rough-walled fracture model can improve the accuracy of fluid flow simulations by approximately 14.99%–19.77%, compared with the commonly used single-rough-walled fracture model. The ratio of flow rate to hydraulic gradient increases by one order of magnitude for fluids in a linear flow regime with increment of shear displacement from 2.2 mm to 2.6 mm. By solving the NS equations, the inertial effect is taken into account and the significant eddies are simulated and numerically visualized, which are not easy to be captured in conventional experiments. The anisotropy of fluid flow in the linear regime during shearing is robustly enhanced as the shearing advances; however, it is either increased or decreased for fluids in the nonlinear flow regime, depending on the geometry of shear-induced void spaces between the two rough walls of the fracture. The present study provides a method to represent the real geometry of fractures during shearing and to simulate fluid flow by directly solving the NS equations, which can be potentially utilized in many applications such as heat and mass transfer, contaminant transport, and coupled hydro-thermo-mechanical processes within rock fractures/fracture networks.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 16 December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Chun-Liang Zhang, Ben Laurich〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The mechanical behavior of sandy facies of Opalinus Clay at the Mont Terri underground rock laboratory (URL) in Switzerland was investigated with drained and undrained triaxial compression and extension, cyclic compression, and creep tests. Samples were taken from boreholes drilled parallel to bedding. Most of the samples were reconditioned to minimize sampling effects of desaturation and micro-cracking. The compression was accomplished by increasing axial stress at constant radial stress. The extension was carried out by increasing radial stress at constant axial stress. Moreover, extension was also achieved by simultaneously increasing radial stress and decreasing axial stress under constant mean stress. The test results showed elastoplastic stress-strain behavior with volumetric compaction until onset of dilatancy at high deviatoric stresses above 80%–90% of the peak failure strength. The strength is dependent upon load path and mean stress. The strength under triaxial compression is higher than that under extension. The respective strength increases with increasing mean stress. Desaturation enhances the stiffness and strength of the claystone. The deformation and strength of the claystone are time-dependent. Under constant deviatoric stress, the claystone crept continuously with time, which can be characterized by a transient phase and a following stationary phase, and even a tertiary phase at high deviatoric stresses to rupture. © 2019 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 2 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Gaoming Lu, Xiating Feng, Yuanhui Li, Xiwei Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The realisation of microwave-induced fracturing of hard rocks has potential significance for microwave-assisted mechanical rock fracturing and stress release in deep rock masses. In this context, compact basalts were treated by microwave heating in a multi-mode cavity at a frequency of 2450 MHz, and then, we investigated the mechanical behaviour of basalt samples after microwave treatment under uniaxial compression and conventional triaxial compression (CTC) tests. After microwave exposure, cracks appeared on the surface and inside of the rock sample, and the temperature of the sample’s surface was unevenly distributed. The results show that the conventional triaxial compressive strength (CTCS) of basalt samples decreased linearly with microwave exposure time, and the higher the confining pressure, the smaller the reduction in the strength of basalt samples after microwave treatment. Under uniaxial compression, microwave exposure greatly affected the axial deformation, suggesting that deformation resistance of the samples gradually decreases with increasing microwave exposure time. Under triaxial compression, some microcracks induced by microwave exposure closed due to the effect of confining pressure, resulting in the confining pressure inhibiting any rightward shift of the axial deformation curve. Furthermore, under uniaxial compression, the elastic modulus and Poisson’s ratio of basalts also decreased in a quasi-linear manner with elapsed microwave exposure time. Under triaxial compression, microwave exposure has slight influence on elastic modulus and Poisson’s ratio. After microwave treatment, the changes in rock strength and deformation mainly result from changes in between the mineral structures. Confining pressure results in the closure of microcracks produced by microwave exposure, so that effects of microwave treatment on strength and deformation decrease, thus reducing the influence on elastic constants. The cohesion decreases with increasing microwave exposure time and shows an approximately linear decrease over time. In the basalt samples, new microcracks in various directions generated by microwave exposure can increase the discreteness of test results, while the discreteness of test results caused by microcracks gradually reduces with increasing confining pressure.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 14 December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Sen Wen, Chunshun Zhang, Yulin Chang, Ping Hu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Layered rock mass of significant strength changes for adjacent layers is frequently observed in underground excavation, and dynamic loading is a prevalent scenario generated during excavation. In order to improve the driving efficiency and reduce engineering accidents, dynamic compression characteristics of this kind of rock mass should be understood. The dynamic properties of a layered composite rock mass are investigated through a series of rock tests and numerical simulations. The rock mass is artificially made of various proportions of sand, cement and water to control the distinct strength variations at various composite layers separated by parallel bedding planes. All rock specimens are prefabricated in a specially designed mould and then cut into 50 mm in diameter and 50 mm in height for split Hopkinson pressure bar (SHPB) dynamic compression testing. The test results reveal that increasing strain rate causes the increases of peak strength, 〈em〉σ〈/em〉〈sub〉p〈/sub〉, and the corresponding failure strain, 〈em〉ε〈/em〉〈sub〉p〈/sub〉, while the dynamic elastic modulus, 〈em〉E〈/em〉〈sub〉d〈/sub〉, remains almost unchanged. Interestingly, under the same strain rates, 〈em〉E〈/em〉〈sub〉d〈/sub〉 of the composite rock specimen is found to decline first and then increase as the dip angle of bedding plane increases. The obtained rock failure patterns due to various dip angles lead to failure modes that could be classified into four categories from our dynamic tests. Also, a series of counterpart numerical simulations has been undertaken, showing that dynamic responses are in good agreement with those obtained from the SHPB tests. The numerical analysis enables us to look into the dynamic characteristics of the composite rock mass subjected to a broader range of strain rates and dip angles than these being tested.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 14 December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Qiuhao Du, Xiaoli Liu, Enzhi Wang, Jianping Zuo, Weimin Wang, Yujie Zhu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉There are a large number of abandoned coalmines in China, and most of them are located around major coal-fired power stations, which are the largest emission sources of carbon dioxide (CO〈sub〉2〈/sub〉). Considering the injection of CO〈sub〉2〈/sub〉 into abandoned coalmines, which are usually in the flooded condition, it is necessary to investigate the effect of CO〈sub〉2〈/sub〉–water–coal interaction on minerals and pore structures at different pressures, temperatures and times. It reveals that the CO〈sub〉2〈/sub〉–water–coal interaction can significantly improve the solubility of Ca, S, Mg, K, Si, Al, Fe and Na. By comparing the mineral content and pore structure before and after CO〈sub〉2〈/sub〉–water–coal interaction, quartz and kaolinite were found to be the main secondary minerals, which increased in all samples. The structures of micropores and mesopores in the range of 1.5–8 nm were changed obviously. Specific surface areas and pore volumes first increased and then decreased with pressure and time, while both increased with temperature. By using the Frenkel–Halsey–Hill model, the fractal dimensions of all samples were analyzed based on 〈em〉D〈/em〉〈sub〉s1〈/sub〉 and 〈em〉D〈/em〉〈sub〉s2〈/sub〉, which reflected the complexities of the pore surface and pore volume, respectively. The results show that fractal dimensions had very weak positive correlations with the carbon content. 〈em〉D〈/em〉〈sub〉s1〈/sub〉 had a positive correlation with the quartz and kaolinite contents, while 〈em〉D〈/em〉〈sub〉s2〈/sub〉 had a negative correlation with the quartz and kaolinite contents.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 30 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Abbasali TaghaviGhalesari, Mohsen Isari, Reza Tarinejad, Abdollah Sohrabi-Bidar〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this context, a new boundary element algorithm based on the time-convoluted traction kernels is employed to evaluate the spatially varying earthquake ground motions of the Pacoima dam in the USA subjected to SH, SV and P incident waves. An accurate three-dimensional (3D) model of the dam canyon is implemented into the computer code BEMSA to investigate the seismic response of the dam. The analyses are performed in time domain with a linearly elastic constitutive model for the medium. This modeling procedure has been validated by the results reported in the existing literature. According to the results of this study, the response of the dam to earthquake waves is generally influenced by predominant frequency of the incident motion, surface topography, relative distance of observation points, and type of the incident seismic wave. For the cases considered, the incident SV wave has led to the maximum amplification of incident motions, especially at the left side of the dam. The results indicate that the proposed procedure can be employed for accurate prediction of a dam response during an earthquake.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 10 December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Aswin Lim, Petra Cahaya Atmaja, Siska Rustiani〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This article presents an innovative method of bio-mediated soil improvement for increasing the shear strength of loose sand. The improvement is realized by mixing the loose sand with the inoculum of Rhizopus oligosporus〈em〉,〈/em〉 a kind of fungus widely used in food industry for making Indonesian tempeh. The objective of this article is to investigate the performance and mechanism of mixing tempeh inoculum as a binding agent of loose sand particles. The inoculum dosage, water content of loose sand, and curing time were examined for identifying the increment of unconfined compressive strength (〈em〉q〈/em〉〈sub〉u〈/sub〉) of the samples. The results showed that 〈em〉q〈/em〉〈sub〉u〈/sub〉 of the treated samples increased when the inoculum dosage was elevated. It shows that 5.24% inoculum could yield 68 kPa of 〈em〉q〈/em〉〈sub〉u〈/sub〉, and 5% water content and 3 d curing time produced the maximum 〈em〉q〈/em〉〈sub〉u〈/sub〉. Moreover, the mechanism of hypha and mycelium in binding the soil particles was clearly observed using a digital microscope and scanning electron microscope.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 27 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Charlie C. Li, Peter Mikula, Brad Simser, Bruce Hebblewhite, William Joughin, Xiaowei Feng, Nuwen Xu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The paper is a summary of discussions on four topics in rockburst and dynamic ground support. Topic 1 is the mechanisms of rockburst. Rockburst events are classified into two categories in accordance with the triggering mechanisms, i.e. strain burst and fault-slip burst. Strain burst occurs on rock surfaces when the tangential stress exceeds the rock strength in hard and brittle rocks. Fault-slip burst is triggered by fault-slip induced seismicity. Topic 2 is prediction and forecasting of rockburst events. Prediction for a rockburst event must tell the location, timing and magnitude of the event. Forecasting could simply foresee the probability of some of the three parameters. It is extremely challenging to predict rockbursts and large seismic events with current knowledge and technologies, but forecasting is possible, for example the possible locations of strain burst in an underground opening. At present, the approach using seismic monitoring and numerical modelling is a promising forecasting method. Topic 3 is preconditioning methods. The current preconditioning methods are blasting, relief-hole drilling and hydrofracturing. Defusing fault-slip seismicity is difficult and challenging but has been achieved. In very deep locations (〉3000 m), the fracturing could extend from the excavation face to a deep location ahead of the face and therefore preconditioning is usually not required. Topic 4 is dynamic ground support against rockburst. Dynamic ground support requires that the support system be strong enough to sustain the momentum of the ejecting rock on one hand and tough enough on the other hand to absorb the strain and seismic energies released from the rock mass. The current dynamic support systems in underground mining are composed of yielding tendons and flexible surface retaining elements like mesh/screen and straps. Yielding props and engineered timber props are also used for dynamic support.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 13 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Xing Li, Jian Zhao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉This review summarizes the development of particle-based numerical manifold method (PNMM) and its applications to rock dynamics. The fundamental principle of numerical manifold method (NMM) is first briefly introduced. Then, the history of the newly developed PNMM is given. Basic idea of PNMM and its simulation procedure are presented. Considering that PNMM could be regarded as an NMM-based model, a comparison of PNMM and NMM is discussed from several points of view in this paper. Besides, accomplished applications of PNMM to the dynamic rock fracturing are also reviewed. Finally, some recommendations are provided for the future work of PNMM.〈/p〉 〈p〉© 2019 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (〈a href="https://creativecommons.org/" target="_blank"〉http://creativecommons.org/〈/a〉〈/p〉 〈p〉licenses/by-nc-nd/4.0/).〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 13 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Nezam Bozorgzadeh, John P. Harrison〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Reliability-based design (RBD) is being adopted by geotechnical design codes worldwide, and it is therefore necessary that rock engineering practice evolves to embrace RBD. This paper examines the Hoek-Brown (H-B) strength criterion within the RBD framework, and presents three distinct analyses using a Bayesian approach. Firstly, a compilation of intact compressive strength test data for six rock types is used to examine uncertainty and variability in the estimated H-B parameters 〈em〉m〈/em〉 and 〈em〉σ〈/em〉〈sub〉c〈/sub〉, and corresponding axial strength predicted. The results suggest that within and between rock types, variability is so large that these parameters need to be determined from rock testing campaigns, rather than reference values being used. The second analysis uses an extensive set of compressive and tensile (both direct and indirect) strength data for a granodiorite, together with a new Bayesian regression model, to develop joint probability distributions of 〈em〉m〈/em〉 and 〈em〉σ〈/em〉〈sub〉c〈/sub〉 suitable for use in RBD. This analysis also shows how compressive and indirect tensile strength data may be robustly used to fit an H-B criterion. The third analysis uses the granodiorite data to investigate the important matter of developing characteristic strength criteria. Using definitions from Eurocode 7, a formal Bayesian interpretation of characteristic strength is proposed and used to analyse strength data to generate a characteristic criterion. These criteria are presented in terms of characteristic parameters 〈em〉m〈/em〉〈sub〉k〈/sub〉 and 〈em〉σ〈/em〉〈sub〉ck〈/sub〉, the values of which are shown to depend on the testing regime used to obtain the strength data. The paper confirms that careful use of appropriate Bayesian statistical analysis allows the H-B criterion to be brought within the framework of RBD. It also reveals that testing guidelines such as the International Society for Rock Mechanics and Rock Engineering (ISRM) suggested methods will require modification in order to support RBD. Importantly, the need to fully understand the implications of uncertainty in nonlinear strength criteria is identified.〈/p〉 〈p〉© 2019 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (〈a href="https://creativecommons.org/licenses/by-nc-nd/4.0/" target="_blank"〉http://creativecommons.org/licenses/by-nc-nd/4.0/〈/a〉).〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 13 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Aida Mehrpazhouh, Seyed Naser Moghadas Tafreshi, Mehdi Mirzababaei〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Pavements constructed over loosely compacted subgrades may not possess adequate California bearing ratio (CBR) to meet the requirements of pavement design codes, which may lead to a thicker pavement design for addressing the required strength. Geosynthetics have been proven to be effective for mitigating the adverse mechanical behaviors of weak soils as integrated constituents of base and sub-base layers in road construction. This study investigated the behaviors of unreinforced and reinforced sand with nonwoven geotextile using repeated CBR loading test (followed by unloading and reloading). The depth and number of geotextile reinforcement layers, as well as the compaction ratio of the soil above and below the reinforcement layer(s) and the compaction ratio of the sand bed, were set as variables in this context. Geotextile layers were placed at upper thickness ratios of 0.3, 0.6 and 0.9 and the lower thickness ratio of 0.3. The compaction ratios of the upper layer and the sand bed varied between 85% and 97% to simulate a dense layer on a medium dense sand bed for all unreinforced and reinforced testing scenarios. Repeated CBR loading tests were conducted to the target loads of 100 kg.f, 150 kg.f, 200 kg.f and 400 kg.f, respectively (1 kg.f = 9.8 N). The results indicated that placing one layer of reinforcement with an upper thickness ratio of 0.3 and compacting the soil above the reinforcement to compaction ratio of 97% significantly reduced the penetration of the CBR piston for all target repeated load levels. However, using two layers of reinforcement sandwiched between two dense soil layers with a compaction ratio of 97% with upper and lower thickness ratios of 0.3 resulted in the lowest penetration.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering, Volume 11, Issue 3〈/p〉 〈p〉Author(s): E.T. Brown〈/p〉

Beschreibung: 〈p〉Publication date: Available online 29 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Brendan T. Scott, Mark B. Jaksa, Peter W. Mitchell〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The influence of towing speed on the effectiveness of the 4-sided impact roller using earth pressure cells (EPCs) is investigated. Two field trials were undertaken; the first trial used three EPCs placed at varying depths between 0.5 m and 1.5 m with towing speeds of 9-12 km/h. The second used three EPCs placed at a uniform depth of 0.8 m, with towing speeds of 5-15 km/h. The findings from the two trials confirmed that towing speed influences the pressure imparted to the ground and hence compactive effort. This paper proposes that the energy imparted to the ground is best described in terms of work done, which is the sum of the change in both potential and kinetic energies. Current practice of using either kinetic energy or gravitational potential energy should be avoided as neither can accurately quantify rolling dynamic compaction (RDC) when towing speed is varied.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Rohola Hasanpour, Jamal Rostami, Jürgen Schmitt, Yilmaz Ozcelik, Babak Sohrabian〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study presents an application of artificial neural network (ANN) and Bayesian network (BN) for evaluation of jamming risk of the shielded tunnel boring machines (TBMs) in adverse ground conditions such as squeezing grounds. The analysis is based on database of tunneling cases by numerical modeling to evaluate the ground convergence and possibility of machine entrapment. The results of initial numerical analysis were verified in comparison with some case studies. A data set was established by performing additional numerical modeling of various scenarios based on variation of the most critical parameters affecting shield jamming. This includes compressive strength and deformation modulus of rock mass, tunnel radius, shield length, shield thickness, in situ stresses, depth of over-excavation, and skin friction between shield and rock. Using the data set, an ANN was trained to predict the contact pressures from a series of ground properties and machine parameters. Furthermore, the continuous and discretized BNs were used to analyze the risk of shield jamming. The results of these two different BN methods are compared to the field observations and summarized in this paper. The developed risk models can estimate the required thrust force in both cases. The BN models can also be used in the cases with incomplete geological and geomechanical properties.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 6 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Hadi Abioghli, Amir Hamidi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The aim of this study is to present a constitutive model for prediction of the mechanical behavior of fiber-reinforced cemented sand. For this purpose, a generalized plasticity constitutive model of sandy soil is selected and the parameters of the model are determined for three types of sandy soils using the results of triaxial tests. Next, the proposed model is developed using the existing models based on the physico-mechanical characteristics of fiber-reinforced cemented sand. The elastic parameters, flow rule and hardening law of the base model are modified for fiber-reinforced cemented sand. To verify the proposed model, the predicted results are compared with those of triaxial tests performed on fiber-reinforced cemented sand. Finally, the efficiency of the proposed model is studied at different confining pressures, and cement and fiber contents.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 26 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): R.A.T.M. Ranasinghe, M.B. Jaksa, F. Pooya Nejad, Y.L. Kuo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Rolling dynamic compaction (RDC), which employs non-circular module towed behind a tractor, is an innovative soil compaction method that has proven to be successful in many ground improvement applications. RDC involves repeatedly delivering high-energy impact blows onto the ground surface, which improves soil density and thus soil strength and stiffness. However, there exists a lack of methods to predict the effectiveness of RDC in different ground conditions, which has become a major obstacle to its adoption. For this, in this context, a prediction model is developed based on linear genetic programming (LGP), which is one of the common approaches in application of artificial intelligence for nonlinear forecasting. The models are based on in situ density-related data in terms of dynamic cone penetrometer (DCP) results obtained from several projects that have employed the 4-sided, 8-t impact roller (BH-1300). It is shown that the model is accurate and reliable over a range of soil types. Furthermore, a series of parametric studies confirms its robustness in generalizing data. In addition, the results of the comparative study indicate that the optimal LGP model has a better predictive performance than the existing artificial neural network (ANN) model developed earlier by the authors.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 3 May 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Rock Mechanics and Geotechnical Engineering〈/p〉 〈p〉Author(s): Danial Jahed Armaghani, Mohammadreza Koopialipoor, Aminaton Marto, Saffet Yagiz〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉This study aims to develop several optimization techniques for predicting advance rate of tunnel boring machine (TBM) in different weathered zones of granite. For this purpose, extensive field and laboratory studies have been conducted along the 12,649 m of the Pahang – Selangor raw water transfer tunnel in Malaysia. Rock properties consisting of uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), rock mass rating (RMR), rock quality designation (RQD), quartz content (〈em〉q〈/em〉) and weathered zone as well as machine specifications including thrust force and revolution per minute (RPM) were measured to establish comprehensive datasets for optimization. Accordingly, to estimate the advance rate of TBM, two new hybrid optimization techniques, i.e. an artificial neural network (ANN) combined with both imperialist competitive algorithm (ICA) and particle swarm optimization (PSO), were developed for mechanical tunneling in granitic rocks. Further, the new hybrid optimization techniques were compared and the best one was chosen among them to be used for practice. To evaluate the accuracy of the proposed models for both testing and training datasets, various statistical indices including coefficient of determination (〈em〉R〈/em〉〈sup〉2〈/sup〉), root mean square error (RMSE) and variance account for (VAF) were utilized herein. The values of 〈em〉R〈/em〉〈sup〉2〈/sup〉, RMSE, and VAF ranged between 0.939–0.961, 0.022–0.036, and 93.899–96.145, respectively, with the PSO-ANN hybrid technique demonstrating the best performance. It is concluded that both the optimization techniques, i.e. PSO-ANN and ICA-ANN, could be utilized for predicting the advance rate of TBMs; however, the PSO-ANN technique is superior.〈/p〉 〈p〉© 2019 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (〈a href="https://creativecommons.org/licenses/by-nc-nd/4.0/" target="_blank"〉http://creativecommons.org/licenses/by-nc-nd/4.0/〈/a〉)〈/p〉 〈/div〉 〈/div〉