ALBERT

Description: Publication date: Available online 11 September 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Saurabh Rawat, Ashok K. Gupta, Anil Dhiman An internal failure mode for a soil – nailed system consists of failure at nail heads, slope facing, nail strength, along grout-soil interface and pullout failure. A better understanding of pullout of soil nail thus becomes important to assess the stability of a soil - nailed system. In the present study an investigation on pullout behaviour of soil nail with circular discs along the shaft has been carried out by a Three - Dimensional Finite Element Analysis using Abaqus/Explicit routine. A total of 67 simulations have been carried out to accurately predict the pullout behaviour of soil nail. The soil nail under study has circular discs along its shaft varying in numbers from 1 to 4. The pullout of this soil nail in a pullout test box has been simulated with a constant overburden of 20 kN/m 2 acting on the nail. The pullout load - displacement characteristics, stresses around soil nail and failure mechanism during pullout are studied. Variation of dimensionless factors such as normalized pullout load factor and bearing capacity factor has been carried out with different combinations of parameters in terms of relative disc spacing ratio, anchorage length ratio, embedment ratio, diameter ratio and displacement ratio. From the results of analysis, it is found that nail with higher number of circular discs resorts to a high pullout load. There is a critical relative disc spacing ratio and diameter ratio which significantly affects the pullout behaviour of nail.

Description: Publication date: Available online 8 August 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Isabelle Thenevin, Laura Blanco-Martín, Faouzi Hadj-Hassen, Jacques Schleifer, Zbigniew Lubosik, Aleksander Wrana Laboratory pull-out tests were conducted on the following rock bolts and cable bolts: steel rebars, smooth steel bars, fiberglass reinforced polymer threaded bolts, flexible cable bolts, IR5/IN special cable bolts and Mini-cage cable bolts. The diameter of the tested bolts was between 16 mm and 26 mm. The bolts were grouted in a sandstone sample using resin or cement grouts. The tests were conducted under either constant radial stiffness or constant confining pressure boundary conditions applied on the outer surface of the rock sample. In most tests, the rate of displacement was about 0.02 mm/s. The tests were performed using a pull-out bench that allows testing a wide range of parameters. This paper provides an extensive database of laboratory pull-out test results and confirms the influence of the confining pressure and the embedment length on the pull-out response (rock bolts and cable bolts). It also highlights the sensitivity of the results to the operating conditions and to the behaviour of the sample as a whole, which cannot be neglected when the test results are used to assess the bolt-grout or the grout-rock interface.

Description: Publication date: Available online 18 September 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): A.P. Morris, D.A. Ferrill, G.R. Walter, A.M. Price, K.J. Smart, R.J. Skoumal, M.R. Brudzinski, B.S. Currie Abstract The Youngstown earthquake sequence of 2011 is one of the clearest examples of inadvertently induced seismicity for which detailed documentation is available. In this paper, we investigate (i) likely stress states in the vicinity of the injection well, (ii) a range of likely permeability scenarios, and (iii) relatively simple methods by which induced seismicity can be evaluated and mitigated. We use relocated hypocenters from the seismic sequence to construct a basement fault structure, which is then used to serve as a reference surface within the basement, and on which we calculate the effects of pore pressure changes induced by the injection activities of the Northstar #1 injection well. We also deduce an in situ (pre-injection) strike-slip stress regime, where σ 2 ≈ σ 3 , and it is consistent with both recent earthquake data and published stress estimates for the region. If the reactivation characteristics of the basement are known or assumed, a critical or threshold slip tendency can be determined and the basement faults can be analyzed for the likelihood of reactivation in a perturbed pore pressure field. Comparison of well injection pressures and simulated pore pressure perturbations within the basement below the injection well indicates that permeability anisotropy is necessary to generate sufficient pore pressure perturbation to induce fault reactivation. Simulations of the well’s injection history show that our estimate of in situ stress state, coupled with a highly anisotropic permeability structure, can generate sufficient pore pressure perturbation on the inferred basement structure to cause reactivation, potentially slipping an area of approximately 4×10 5 m 2 .

Description: Publication date: Available online 22 September 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): I. Ferestade, P. Hosseini Tehrani, R. Heidary Ballast is a layer composed of crushed stone basically with diameters of 20–60 mm, on which sleepers and rails are set. Ballast is used to withstand vertical, horizontal and lateral forces applied on sleepers and to hold the line in operative conditions. Ballast deterioration induced by crashed stones is a major issue of track instability as the ballast layer quality depending on the materials used and their densities should be focused on. Therefore, ballast should be resistant against loads applied, and the fracture toughness of ballast stone is of great importance. For this purpose, the fracture toughness of two kinds of ballast stones used in Iranian railway, i.e. Gaduk (limestone) and Anjylavnd (andesite), is investigated experimentally in this paper. The quality of ballast stone is evaluated in different weather conditions. Numerical results shown that the Anjylavnd stone is more appropriate for rainy and cold weather when there is a probability of fracturing due to frozen water captured in ballast.

Description: Publication date: Available online 14 September 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Sohrab Salehin The quality of designed structures embedded in rocks is strongly related to rock strength parameters of intact rock. Measuring different parameters from tests could be very expensive in designing phase of projects. Estimating some parameters from other ones can reduce costs and time of project procedure. In this paper, the relationships between static and dynamic parameters of marls are studied by using the single and multiple linear regressions. For this purpose, several marl core samples from Seydoon region, Khoozestan Province in Iran are collected and tested. Some equations with sufficient correlation have been obtained to predict the engineering parameters of marls, especially the uniaxial compressive strength (UCS).

Description: Publication date: Available online 23 September 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Francisco Lamas-Lopez, Yu-Jun Cui, Nicolas Calon, Sofia Costa D’Aguiar, Tongwei Zhang For the 30,000 km French conventional railway lines (94 % of the whole network), the speed is currently limited to 220 km/h, to be compared with the speed of 320 km/h for the 1,800 km high speed lines. Nowadays, there is a growing need to improve the service by increasing the speed limit for the conventional lines. This paper aims at studying the influence of train speed on the mechanical behaviour of track-bed materials based on field monitoring data. Emphasis is put on the behaviour of interlayer and subgrade soils. The selected experimentation site is located in Vierzon, France. Several sensors including accelerometers and soil pressure gauges were installed at different depths. The vertical strain of different layers can be obtained by integrating the records of accelerometers installed at different track-bed depths. The experimentation was carried out using an intercity test train running at different speeds, from 60 to 200 km/h. This test train was composed of a locomotive (22.5 Mg/axle) and 7 ‘Corail’ coaches (10.5 Mg/axle). It was observed that when the train speed was raised, the loadings transmitted to track-bed increased. Moreover, the response of the track-bed materials was amplified by the speed rise at different depths: the vertical dynamic stress was increased by about 10% when the train speed was raised from 60 km/h to 200 km/h for the locomotive loading, and the vertical strains doubled their quasi-static values in the shallow layers. Moreover, the stress-strain paths were estimated using the vertical stress and vertical strain for each train speed. These loading paths allowed the resilient modulus M r to be determined. It was found that M r decreased by about 10 % when the train speed was increased from 100 km/ to 200 km/h. However, the damping ratio D r kept stable in the range of speeds explored.

Description: Publication date: Available online 18 September 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Qidong Gao, Wenbo Lu, Yingguo Hu, Zhaowei Yang, Peng Yan, Ming Chen The shear wave (S-wave) component of the total blast vibration always plays an important role in damage to rock or adjacent structures. The numerical simulation approach has been received as an economical and effective one in predicting the blast vibration. However, S-wave has not yet attracted enough attention in previous numerical simulations. Three typical numerical models, i.e. the continuum-based elastic model, the continuum-based damage model, and the coupled Smoothed Particle Hydrodynamics - Finite Element Method model, were first introduced and developed to simulate the blasting of a single cylindrical charge. Then the numerical results from different models were comprehensively evaluated based on the review on the generation mechanisms of S-wave during blasting. Finally, some valuable suggestions on the selection of numerical approaches in simulating the generation of blast-induced S-wave were put forward. Results indicate that different numerical models produce different results of S-wave. The coupled numerical model is chosen as the best one among the three, for its outstanding capacity in producing S-wave components. It is suggested that the model that can describe the cracking, sliding or heaving of rock mass, and movement of fragments near the borehole should be selected preferentially, and priority should be given to the material constitutive law that could record the nonlinear mechanic behavior of rock mass near the borehole.

Description: Publication date: Available online 10 August 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Yifei Sun, Chen Chen, Sanjay Nimbalkar Grading has long been recognized to critically influence the mechanical behaviour of ballast. To identify the ballast grading for heavy-haul rail track, monotonic and cyclic triaxial tests are conducted to assess the performances of different gradings. Permanent deformations, aggregates degradation, resilience, shear resistance, maximum and minimum densities are recorded and analysed. The grading is found to affect the behaviour of ballast in that coarser gradings exhibit relatively better strength, resilience and therefore less permanent deformation. However, ballast degradation increases with the overall aggregate size. Therefore, to identify the grading for ballast with different performance objectives, a grey relational theory is used to convert the multi-objective into single-objective, i.e. grey relational grade. A relatively optimal grading that provides the highest grey relational grade is thus suggested for the improved ballast performance.

Description: Publication date: Available online 14 August 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Asskar Janalizadeh Choobbasti, Saman Soleimani Kutanaei An experimental program was conducted to explore the impact of nanosilica on the microstructure and mechanical characteristics of cemented sandy soil. Cement agent included Portland cement type II. Cement content was 6% by weight of the sandy soil. Nanosilica was added in percentages of 0%, 4%, 8% and 12% by weight of cement. Cylindrical samples were prepared with relative density of 80% and optimum water content and cured for 7 d, 28 d and 90 d. Microstructure characteristics of cement-nanosilica-sand mixtures after 90 d of curing have been explored using atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. Effects of curing time on microstructure properties of cemented sandy soil samples with 0% and 8% nanosilica have been investigated using SEM test. Unconfined compression test (for all curing times) and compaction test were also performed. The SEM and AFM tests results showed that nanosilica contributes to enhancement of cemented sandy soil through yielding denser, more uniform structure. The XRD test demonstrated that the inclusion of nanosilica in the cemented soil increases the intensity of the calcium silicate hydrate (CSH) peak and decreases the intensity of the calcium hydroxide (CH) peak. The results showed that adding optimum percentages of nanosilica to cement-stabilized sandy soil enhances its mechanical and microstructure properties.

Description: Publication date: Available online 13 June 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): N. Salih, A. Mohammed In order to understand the effects of soaking time and confined water pressure on the strength of rock due to dissolution of gypsum, rock samples with 96% of gypsum content collected from Kurdistan Region in northern Iraq were investigated. Laboratory tests were then performed on the normal gypsum rock samples under pre-saturated condition to obtain their uniaxial compressive strength (UCS) values. The pre-saturated samples were submerged in distilled water for 35 d, 70 d and 105 d, respectively, under confined water pressures of 0−0.5 MPa. The gypsum content decreased by 11% after 105 d of soaking under confined water pressure of 0.5 MPa. The UCS of the normal gypsum rock was 19.6 MPa and it decreased to 6.3 MPa and 2 MPa after 105 d of soaking under confined water pressures of 0 and 0.5 MPa, respectively. A nonlinear constitutive model was used to simulate the experimental stress-strain relationships of rock samples under various conditions. The constitutive model parameters were sensitive to the gypsum content.

Description: Publication date: Available online 28 June 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Xibing Li, Fengqiang Gong, Ming Tao, Longjun Dong, Kun Du, Chunde Ma, Zilong Zhou, Tubing Yin Rock failure phenomena, such as rockburst, slabbing (or spalling) and zonal disintegration, related to deep underground excavation of hard rocks are frequently reported and pose a great threat to deep mining. Currently, the explanation for these failure phenomena using existing dynamic or static rock mechanics theory is not straightforward. In this study, new theory and testing method for deep underground rock mass under coupled static-dynamic loading are introduced. Two types of coupled loading modes, i.e. “critical static stress + slight disturbance” and “elastic static stress + impact disturbance”, are proposed, and associated test devices are developed. Rockburst phenomena of hard rocks under coupled static-dynamic loading are successfully reproduced in the laboratory, and the rockburst mechanism and related criteria are demonstrated. The results of true triaxial unloading compression tests on granite and red sandstone indicate that the unloading can induce slabbing when the confining pressure exceeds a certain threshold, and the slabbing failure strength is lower than the shear failure strength according to the conventional Mohr-Column criterion. Numerical results indicate that the rock unloading failure response under different in situ stresses and unloading rates can be characterized by an equivalent strain energy density. In addition, we present a new microseismic source location method without premeasuring the sound wave velocity in rock mass, which can efficiently and accurately locate the rock failure in hard rock mines. Also, a new idea for deep hard rock mining using a non-explosive continuous mining method is briefly introduced.

Description: Publication date: Available online 1 July 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Maral Goharzay, Ali Noorzad, Ahmadreza Mahboubi Ardakani, Mostafa Jalal In this context, two different approaches of soil liquefaction evaluation using a soft computing technique based on the worldwide standard penetration test (SPT) databases have been studied. Gene expression programming (GEP) as a gray-box modeling approach is used to develop different deterministic models in order to evaluate the occurrence of soil liquefaction in terms of liquefaction field performance indicator ( LI ) and factor of safety ( F s ) in logistic regression and classification concepts. The comparative plots illustrate that the classification concept-based models show a better performance than those based on logistic regression. In the probabilistic approach, a calibrated mapping function is developed in the context of Bayes’ theorem in order to capture the failure probabilities ( P L ) in the absence of the knowledge of parameter uncertainty. Consistent results obtained from the proposed probabilistic models, compared to the most well-known models, indicate the robustness of the methodology used in this study. The probability models provide a simple, but also efficient decision-making tool in engineering design to quantitatively assess the liquefaction triggering thresholds.

Description: Publication date: Available online 1 July 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Mounir Belghali, Zied Saada, Denis Garnier, Samir Maghous The stability analysis of passive bolt-reinforced rock slopes under seismic loads is investigated within the framework of the kinematic approach of limit analysis theory. A pseudo-static method is adopted to account for the inertial forces induced in the rock mass by seismic events. The strength properties of the rock material are described by a modified Hoek-Brown strength criterion, whereas the passive bolts are modeled as bar-like inclusions that exhibit only resistance to tensile-compressive forces. Taking advantage of the ability to compute closed-form expressions for the support functions associated with the modified Hoek-Brown strength criterion, a rotational failure mechanism is implemented to derive rigorous lower bound estimates for the amount of reinforcement strength to prevent slope failure. The approach is then applied to investigating the effects of relevant geometry, strength and loading parameters in light of a preliminary parametric study. The accuracy of the approach is assessed by comparison of the lower bound estimates with finite element limit analysis solutions, thus emphasizing the ability of the approach to properly predict the stability conditions and to capture the essential features of deformation localization pattern. Finally, the extension of the approach to account for slipping at the interface between reinforcements and surrounding rock mass is outlined.

Description: Publication date: Available online 12 July 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Alaa H.J. Al-Rkaby, A. Chegenizadeh, H.R. Nikraz Although the cyclic rotation of the principal stress direction is important, its effect on the deformation behavior and dynamic properties of reinforced soil have not been reported to date. Tests carried out on large scale hollow cylinder samples reveal that the cyclic rotation of the principal stress direction results in significant development of strain components ( ε z , ε r , ε θ and γ zθ ) with periodic characteristics despite the deviator stress being constant during tests. This oscillation can be related to the corresponding variation in the stress components and the anisotropic fabric that rotated continuously along the principal stress direction. Sand under rotation appears to develop a plastic strain. Similar trends were observed for reinforced sand but shear interaction, interlocking between particles and the reinforcement layer, and the confinement results in significant reduction in the induced strains and associated irrecoverable plastic strains. Most of the strains occurred in the first cycle and as number of cycles increased the presence of strains become very small, almost insignificant. This indicated that the soil had reached anisotropic critical state (ACS), where a stable structure formed after continuous orientation, realignment and rearrangement of the particles that accompanied increasing cyclic rotation. Rotation in the range of 60°-135° produces more induced strains even in the presence of the reinforcement, when compared with other ranges. This relates to the extension mode of the test in this range in which σ θ > σ z and to the relative approach between the mobilised plane and the weakest horizontal plane. Reinforcement results in increased shear modulus while it appears to have no effect on the damping ratio. Continuous cycles of rotation results in an increase in the shear modulus and lower damping ratio due to the densification that resulted in a decrease in shear strain and less dissipation of energy.

Description: Publication date: Available online 20 July 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): S. Liakas, C. O’Sullivan, C. Saroglou The particulate discrete element method (DEM) can be used to capture the response of rock provided appropriate bonding models are used to cement the particles to each other. Simulations of laboratory tests are important to establish the extent to which such models can capture realistic rock behaviour. Hitherto the focus in such comparison studies has either been on homogeneous samples or use of 2D models. In situ, rock formations are often heterogeneous and so exploring the ability this type of model to capture heterogeneous material behaviour is important to facilitate their use in design analysis. In situ stress states are three-dimensional and so it is important to develop 3D models. This contribution revisits an earlier experimental study, which considered the response of heterogeneous samples where the relative proportions of weak material (siltstone) and stronger, hard material (sandstone) was varied in a controlled manner. Using a 3D DEM model with the parallel bond contact model, virtual heterogeneous samples were created. The overall responses in terms of the variation of strength and stiffness with percentage of weaker (siltstone) material were shown to be equivalent to the experimental observations. There was also good qualitative agreement in the failure patterns observed in the experiments and the simulations. The DEM data enabled analysis of the initiation of localizations and micro-fractures in the samples.

Description: Publication date: Available online 1 August 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): M.C. Villeneuve The transition from grinding to chipping can be observed in tunnel boring machine (TBM) penetration test data by plotting the penetration rate (distance/revolution) against the net cutter thrust (force per cutter) over the full range of penetration rates in the test. Correlating penetration test data to the geological and geomechanical characteristics of rock masses through which a penetration test is conducted provides the ability to reveal the efficiency of the chipping process in response to changing geological conditions. Penetration test data can also be used to identify stress-induced tunnel face instability. We show that the strength of the rock is an important control on how much net cutter thrust is required to transition from grinding to chipping. We also show that the geological characteristics of a rock will determine how efficiently chipping occurs once it has begun. In particular, geological characteristics that lead to efficient fracture propagation, such as fabric and mica content, will lead to efficient chipping. These findings will enable a better correlation between TBM performance and geological conditions for use in TBM design, as a basis for contractual payments where penetration rate dominates the excavation cycle and in further academic investigations into the TBM excavation process.

Description: Publication date: Available online 1 August 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Saurabh Rawat, Ashok Kumar Gupta An investigation into the pullout response of helical soil nail using finite element subroutine Plaxis 2D is presented. The numerical modelling of actual pullout response is achieved by axisymmetric and horizontal loading condition. The effect of varying number of helical plates, helical plate spacing and helical plate diameter is studied to understand the pullout capacity behaviour. The failure surfaces for various helical soil nail configurations and their pullout mechanisms are also analysed and discussed. The pullout capacity is found to increase with increase in number of helical plates. The helical plate spacing ratio ( s / D h ) and diameter ratio ( D h / D s ) are found to increase the pullout only up to a critical value. The response of helical soil nail using axisymmetric finite element simulation is found similar to the uplift behaviour of helical piles and helical soil anchors. In the absence of literature regarding numerical modelling of helical soil nail, simulation results are validated with uplift responses of helical piles and soil anchors. A good agreement in their comparative study for pullout response is also observed.

Description: Publication date: Available online 1 August 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Ł. Wojtecki, P. Konicek, J. Schreiber In the Upper Silesian Coal Basin (USCB), coal seams are exploited under progressively more difficult geological and mining conditions (greater depth, higher horizontal stress, more frequent occurrence of competent rock layers, etc.). Mining depth, dislocations and mining remnants in coal seams are the most important factors responsible for the occurrence of rockburst hazards. Longwall mining next to the mining edges of neighbouring coal seams is particularly disadvantageous. The levels of rockburst hazards are minimised via the use of rockburst prevention methods. One active prevention method is torpedo blasting in roof rocks. Torpedo blastings are performed in order to decrease local stress concentrations in rock masses and to fracture the roof rocks to prevent or minimise the impact of high-energy tremors on excavations. The estimation of the effectiveness of torpedo blasting is particularly important when mining is under difficult geological and mining conditions. Torpedo blasting is the main form of active rockburst prevention in the assigned colliery in the Polish part of the USCB. The effectiveness of blasting can be estimated using the seismic effect method, in which the seismic monitoring data and the mass of explosives are taken into consideration. The seismic effect method was developed in the Czech Republic and is always being used in collieries in the Czech part of the coal basin. Now, this method has been widely adopted for our selected colliery in the Polish part of the coal basin. The effectiveness of torpedo blastings in the faces and galleries of the assigned longwall in coal seam 506 has been estimated. The results show that the effectiveness of torpedo blastings for this longwall was significant in light of the seismic effect method, which corresponds to the in situ observations. The seismic effect method is regularly applied to estimating the blasting effectiveness in the selected colliery.

Description: Publication date: Available online 16 October 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Mohammad Mohammadi, Mohammad Farouq Hossaini Rock mass classification systems are the very important part for underground projects and rock mass rating (RMR) is one of the most commonly applied classification systems in numerous civil and mining projects. The type of rock mass consisting of an interbedding of strong and weak layers poses difficulties and uncertainties for determining the RMR. For this, the present paper uses the concept of rock bolt supporting factor (RSF) for modification of RMR system to be used in such rock mass types. The proposed method also demonstrates the importance of rock bolting practice in such rock masses. The geological parameters of the Shemshak Formation of the Alborz Tunnel in Iran are used as case examples for development of the theoretical approach.

Description: Publication date: Available online 25 September 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): M. Jobmann, A. Bebiolka, V. Burlaka, P. Herold, S. Jahn, A. Lommerzheim, J. Maßmann, A. Meleshyn, S. Mrugalla, K. Reinhold, A. Rübel, L. Stark, G. Ziefle In the ANSICHT project that was jointly carried out by DBE TECHNOLOGY GmbH, BGR, and GRS gGmbH, two generic geological site models were used to develop a first draft of a methodology to demonstrate the safety of a high-level waste (HLW) repository in argillaceous formations in Germany, taking into account the regulatory requirements. The main results of the project are characterized by the developed repository concepts adapted to the geological conditions. The specific quantifications of the integrity criteria and their exemplary application with calculational proofs were used to demonstrate the integrity of the host rocks. The development of site-specific FEP (features, events, and processes) catalogues provided a complete system description for evaluation of the repository evolution. The developed work flow of the demonstration concept illustrated the complete sequence of the safety proof in a transparent way. It shows that various steps have to be performed, possibly iteratively, to provide a successful safety proof. The results form a useful tool in the pending search for a HLW repository site, especially when providing a basis for comparing safety analyses of different sites in Germany.

Description: Publication date: Available online 27 September 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Kamel Filali, Badreddine Sbartai This paper estimated the liquefaction potential of a saturated soil deposit subjected to a horizontal seismic excitation at its base using the total stress approach. A comparative analysis between the simplified and the nonlinear dynamic methods was used to verify to what extent the simplified method could be reliable. In order to generalise the reliability of the simplified method for any value of the maximum acceleration for the used earthquakes, a correction for the maximum acceleration less than 0.3 g was proposed based on the comparison of safety factor values determined by the dynamic method illustrated by the equivalent linear model with lumped masses and the simplified method for a given profile of soil subjected to 38 earthquakes. The nonlinear behaviour of soil was represented by two hyperbolic models: Hardin and Drnevich, and Masing. To determine the cyclic resistance ratio (CRR), the cone penetration test (CPT) based methods, the standard penetration test (SPT) based method, and the shear wave velocity based method were used. The safety factor was calculated as the ratio of CRR/CSR, where CSR represents the cyclic stress ratio. The results of the proposed correction have given smaller values of the safety factor compared to the nonlinear dynamic methods for the maximum acceleration less than 0.3 g . In other words, by considering this correction, the most unfavourable case is always given by the modified simplified method.

Description: Publication date: Available online 24 September 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Y.S. Zhao, Z.J. Feng, B.P. Xi, D. Yang, W.G. Liang, Z.J. Wan Deep drilling is becoming the direct and the most efficient means in exploiting deep mineral resources, facilitating to understanding the earthquake mechanism and performing other scientific researches on the Earth’s crust. In order to understand the limit of drilling depth in the Earth’s crust, we first conducted tests on granite samples with respect to the borehole deformation and stability under high temperature and high pressure using the triaxial servo-controlled rock testing system. Then the critical temperature-pressure coupling conditions that result in borehole instability are derived. Finally, based on the testing results obtained and the requirements for the threshold values of borehole deformations during deep drilling, the limit of drilling depth in the Earth’s crust is formulated with ground temperature.

Description: Publication date: Available online 6 October 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Atsushi Sainoki, Hani S. Mitri In the present study, methodologies to evaluate damage around an underground opening due to seismic waves arising from mining-induced fault-slip are examined. First, expressions for an associated flow rule with a failure criterion are developed for biaxial stress conditions, which are implemented into FLAC3D code. A three-dimensional (3D) mine model encompassing a fault running parallel to a steeply dipping orebody is constructed, whereby static and dynamic analyses are performed to extract stopes and simulate fault-slip in dynamic condition, respectively. In the analysis, the developed biaxial model is applied to the stope wall. The fault-slip simulation is performed, considering shearing of fault surface asperities and resultant stress drop driving the fault-slip. Two methodologies to evaluate damage caused by seismic waves arising from the simulated fault-slip are examined: (i) the ratio of dynamic plastic strain increment to elastic strain limit and (ii) plastic strain energy density. For the former one, two types of strain increments are tested, namely effective shear strain increment and volumetric strain increment. The results indicate that volumetric strain increment is a suitable index for detecting damage near the stope wall, while effective shear strain increment is appropriate for evaluating damage in backfill. The evaluation method with plastic strain energy density is found to be capable of assessing damage accumulated in an extensive area caused by rock mass oscillation due to seismic wave propagation. Possible damage to mine developments in the proximity of a stope is clearly described with the index. The comparison of the two methods clarifies that the former one assesses “instantaneous” damage, which is found to be different from “accumulated” damage calculated using plastic strain energy density, in terms of damage area and its location. It is thus concluded that the combination of the two methodologies leads to more accurate damage assessment as a proper measure against rockburst.

Description: Publication date: Available online 16 October 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Mirella Dalvi dos Santos, Kátia Vanessa Bicalho Field tests in geotechnical engineering are fundamental for identification of the underground conditions. The standard penetration test (SPT) is the most commonly used geotechnical approach. There has been an increase both in the use and application of the in situ tests: cone penetration test (CPT) and dynamic probing (DP). Several empirical SPT-CPT and dynamic probing light (DPL)-CPT correlations for sandy soils have been discussed in the literature. New SPT-CPT and DPL-CPT correlations for the sandy soils of the city of Vitoria, in the southeast of Brazil, are suggested in this paper. Statistical analyses to evaluate the quality of the data used are performed, and the suggested correlations are validated with several previous published datasets. The paper also provides some insights into SPT-CPT correlations and soil characteristics (i.e. the mean particle size and the fines fraction of the soil).

Description: Publication date: Available online 16 October 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): W.R. Azzam, A. Basha This article deals with the assessment of the soil nailing technique with a vertical inclusion to improve the geotechnical parameters of cohesive soil. A series of unconfined compression tests and direct shear tests were carried out to establish the stress-strain relationship and strength characteristics of the reinforced clay sample by vertical steel nails. The shear strength performance of the new composite material was tested by varying the number of vertical inclusions, the embedment depth and the alignment radius. The results confirmed that the vertical bars/inclusions shared the vertical applied load with clay. Increase in the number of vertical inclusions significantly increases the shear strength and the stiffness with a remarkable reduction in settlement. When the clay samples were reinforced with six inclusions along the perimeter, the shear strength was increased to 231% for the embedment depth ratio equal to 0.85. To obtain the optimum effect in eliminating shear failure, the vertical inclusions should be extended to a deeper zone with sufficient numbers. It has been found that the vertical inclusions significantly influence the shear strength, and the brittle or general shear failure of the unreinforced sample can be diverted to partial/plastic shear failure.

Description: Publication date: Available online 21 October 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Chuang Liu, Huamin Li, Hani Mitri, Dongjie Jiang, Huigui Li, Junfa Feng The influence of the varying immediate roof thickness on lower strong roof strata movement and failure pattern in longwall coal mining with large mining height is investigated in this paper. The study is based on 58 geological drill holes and hydraulic shield pressure measurements around Panel 42105 of the Buertai Mine in Inner Mongolia, China. The Panel is characterized by relatively soft immediate roof strata of varying thickness superposed by strong strata, herein defined as lower strong roof. A Voussoir beam model is adopted to help interpret the structural movement of the lower strong roof strata and shield pressure measurements. It is shown that when the immediate roof is relatively thick, the broken overlying lower strong lower roof tends to form a stable Voussoir beam with previously broken layer, thus not exerting high pressure on the hydraulic shield and the working face. When the immediate roof is relatively thin, the broken overlying broken lower strong roof tends to behave as a cantilever beam, thus exerting higher pressure on the hydraulic shield and working face. Comparison of model predictions with measured time-weighted average shield pressure (TWAP) shows good agreement.

Description: Publication date: Available online 22 October 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): S. Rezazadeh, A. Eslami Abstract Semi-deep foundations socketed in rocks are considered to be a viable option for the foundations in the presence of heavy load imposed by high-rise structures, due to the low settlement and high bearing capacity. In the optimum design of semi-deep foundations, prediction of the shaft bearing capacity, r s , of foundations socketed in rocks is thus critically important. In this study, the unconfined compressive strength (UCS), q u , has been applied in order to investigate the shaft bearing capacity. For this, a database of 106 full-scale load tests is compiled with UCS values of surrounding rocks, in which 34 tests with rock quality designation (RQD), and 5 tests with rock mass rating (RMR). The bearing rocks for semi-deep foundations include limestone, mudstone, siltstone, shale, granite, tuff, granodiorite, claystone, sandstone, phyllite, schist, and greywacke. Using the database, the applicability and accuracy of the existing empirical methods are evaluated and new relations are derived between the shaft bearing capacity and UCS based on the types of rocks. Moreover, a general equation in case of unknown rock types is proposed and it is verified by another set of data. Since rock-socketed shafts are supported by rock mass (not intact rock), a reduction factor for the compressive strength is suggested and verified in which the effect of discontinuities is considered using the modified UCS, q u(modified) , based upon RMR and RQD in order to take into account the effect of the rock mass properties.

Description: Publication date: Available online 18 December 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Hem Bahadur Motra, Sascha Zertani An increased knowledge of the elastic and geomechnical properties of rocks is important for numerous engineering and geoscience applications (e.g., petroleum geoscience, underground waste repositories, geothermal energy, earthquake studies, and hydrocarbon exploration). To assess the effect of pressure and temperature on seismic velocities and their anisotropy, laboratory experiments were conducted on metamorphic rocks. P- ( V p ) and S-wave ( V s ) velocities were determined on cubic samples of granulites and eclogites with an edge length of 43 mm in a triaxial multianvil apparatus using the ultrasonic pulse emission technique in dependence of changes in pressure and temperature. At successive isotropic pressure states up to 600 MPa and temperatures up to 600 °C, measurements were performed related to the sample coordinates given by the three principal fabric directions (X, Y, Z) representing the foliation (XY plane), the normal to the foliation (Z-direction), and the lineation direction (X-direction). Progressive volumetric strain was logged by the discrete piston displacements. Cumulative errors in V p and V s are estimated to be 〈 1%. Microcrack closure significantly contributes to the increase in seismic velocities and decrease in anisotropies for pressures up to 200-250 MPa. Characteristic P-wave anisotropies of about 10% are obtained for eclogite and 3-4% in a strongly retrogressed eclogite as well as granulites. The wave velocities were used to calculate the geomechanical properties (e.g. density, Poisson’s ratio, volumetric strain, elastic moduli) at different pressure and temperature conditions. These results contribute to the reliable estimate of geomechanical properties of rocks.

Description: Publication date: Available online 26 December 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Rashid Geranmayeh Vaneghi, Behnam Ferdosi, Achola.D. Okoth, Barnabas Kuek Change in mechanical properties of rocks under static loading has been widely studied and documented. However, the response of rocks to cyclic repetitive loads is still a much-debated topic. Fatigue is the phenomenon where rocks under cyclic loading fail at much lower strength as compared to when subjected to the monotonic loading conditions. A few selected cored granodiorite and sandstone specimens have been subjected to uniaxial cyclic compression tests to obtain the unconfined fatigue strength and fatigue life. This study seeks to examine the effect of cyclic loading conditions, loading amplitude and applied stress level on the fatigue life of sandstone, as a soft rock, and granodiorite, as a hard rock, under uniaxial compression test. One aim of this study is determine which of the loading conditions has a stronger effect on rock fatigue response. The fatigue response of hard rocks and soft rocks is also compared. It is shown that the loading amplitude is the most important factor affecting the cyclic response of the tested rocks. The more the loading amplitude, the shorter the fatigue life and the greater the strength degradation. The granodiorite specimens showed more strength degradation compared to the sandstone specimens when subjected to cyclic loading. It is shown that failure modes of specimens under cyclic loadings are different from those under static loadings. More local cracks were observed under cyclic loadings especially for granodiorite rock specimens.

Description: Publication date: Available online 28 December 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Tina Marolt Čebašek, Thomas Frühwirt The aim of this study is to identify the influence of the dip angle of a pre-existing macrocrack on the lifetime and ultimate deformation of rock-like material. Prediction of lifetime has been studied for three groups of specimens under axial static compressive load levels. The specimens were investigated from 65% to 85% of UCS (uniaxial compressive strength) at an interval of 10% of UCS for the groups of specimens with a single modelled open flaw with a dip angle to the loading direction of 30° (first group), at an interval of 5% of UCS increment for the groups of specimens with single (second group), and double sequential open flaws with a dip angle to the loading direction of 60° (third group). This study shows that crack propagation in specimens with a single flaw follows the same sequences. At first, wing cracks appear, and then shear crack develops from the existing wing cracks. Shear cracking is responsible for specimen failure in all three groups. A slip is expected in specimens from the third group which connects two individual modelled open flaws. The moment of the slip is noticed as a characteristic rise in the axial deformation at a constant load level. It is also observed that axial deformation versus time follows the same pattern, irrespective of local geometry. Specimens from the first group exhibit higher axial deformation under different load levels in comparison with the specimens from the second and third groups.

Description: Publication date: Available online 28 December 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): T. Miranda, L.R. Sousa, A.T. Gomes, J. Tinoco, C. Ferreira This paper tries to characterize volcanic rocks through the development and application of an empirical geomechanical system. Geotechnical information was collected from the samples from several Atlantic Ocean islands including Madeira, Azores and Canarias archipelagos. An empirical rock classification system termed as the volcanic rock system (VRS) is developed and presented in detail. Results using the VRS are compared with those obtained using the traditional rock mass rating (RMR) system. Data mining (DM) techniques are applied to a database of volcanic rock geomechanical information from the islands. Different algorithms were developed and consequently approaches were followed for predicting rock mass classes using the VRS and RMR classification systems. Finally, some conclusions are drawn with emphasis on the fact that a better performance was achieved using attributes from VRS.

Description: Publication date: Available online 2 December 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Isaac Vennes, Hani Mitri This study aims to determine if large-scale choked panel destress blasting can provide sufficient beneficial stress reduction in highly-stressed remnant ore pillar that is planned for production. The orebody is divided into 20 stopes over 2 levels, and 2 panels are choke-blasted in the hanging wall to shield the ore pillar by creating a stress shadow around it. A linear-elastic model of the mining system is constructed with finite difference code FLAC3D. The effect of destress blasting in the panels is simulated by applying a fragmentation factor ( α ) to the rock mass stiffness and a stress reduction factor ( β ) to the current state of stress in the region occupied by the destress panels. As an extreme case, the destress panel is also modeled as a void to obtain the maximum possible beneficial effects of destressing and stress shadow. Four stopes are mined in the stress shadow of the panels in 6 lifts and then backfilled. The effect of destress blasting on the remnant ore pillar is quantified based on stress change and brittle shear ratio (BSR) in the stress shadow zone compared to the base case without destress blasting. To establish realistic rock fragmentation and stress reduction factors, model results are compared to measured stress changes reported for case studies at Fraser and Brunswick mines. A 1.5 MPa immediate stress decrease was observed 20 m away from the panel at Fraser Mine, and a 4 MPa immediate stress decrease was observed 25 m away at Brunswick Mine. Comparable results are obtained from the current model with a rock fragmentation factor α of 0.2 and a stress reduction factor β of 0.8. It is shown that a destress blasting with these parameters reduces the major principal stress in the nearest stopes by 10–25 MPa. This yields an immediate reduction of BSR, which is deemed sufficient to reduce volume of ore at risk in the pillar.

Description: Publication date: Available online 5 October 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Amin Manouchehrian, Ming Cai The presence of geological structures such as faults, joints, and dykes has been observed near excavation boundaries in many rockburst case histories. In this paper, the role of discontinuities around tunnels in rockburst occurrence was studied. For this purpose, the Abaqus explicit code was used to simulate dynamic rock failure in deep tunnels. Material heterogeneity was considered using Python scripting in Abaqus. Rockbursts near fault regions in deep tunnels under static and dynamic loads were studied. Several tunnel models with and without faults were built and static and dynamic loads were used to simulate rock failure. The velocity and the released kinetic energy of failed rocks, the failure zone around the tunnel, and the deformed mesh were studied to identify stable and unstable rock failures. Compared with models without discontinuities, the results showed that the velocity and the released kinetic energy of failed rocks were higher, the failure zone around the tunnel was larger, and the mesh was more deformed in the models with discontinuities, indicating that rock failure in the models with discontinuities was more violent. The modeling results confirm that the presence of geological structures in the vicinity of deep excavations could be one of the major influence factors for the occurrence of rockburst. It can explain localized rockburst occurrence in civil tunnels and mining drifts. The presented methodology in this paper for rockburst analysis can be useful for rockburst anticipation and control during mining and tunneling in highly stressed ground.

Description: Publication date: Available online 28 October 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Dariush Javani, Bernt Aadnoy, Mahdi Rastegarnia, Siavash Nadimi, Mohammad Ali Aghighi, Bijan Maleki Production of fines together with reservoir fluid is called solid production. It varies from a few grams or less per ton of reservoir fluid posing only minor problems, to catastrophic amount possibly leading to erosion and complete filling of the borehole. This paper assesses solid production potential in a carbonate gas reservoir located in the south of Iran. Petrophysical logs obtained from the vertical well were employed to construct mechanical earth model. Then, two failure criteria, i.e. Mohr-Coulomb and Mogi-Coulomb, were used to investigate the potential of solid production of the well in the initial and depleted conditions of the reservoir. Using these two criteria, we estimated critical collapse pressure and compared them to the reservoir pressure. Solid production occurs if collapse pressure is greater than pore pressure. Results indicate that the two failure criteria show different estimations of solid production potential of the studied reservoir. Mohr-Coulomb failure criterion estimated solid production in both initial and depleted conditions, where Mogi-Coulomb criterion predicted no solid production in the initial condition of reservoir. Based on Mogi-Coulomb criterion, the well may not require completion solutions like perforated liner, until at least 60% of reservoir pressure was depleted which leads to decrease in operation cost and time.

Description: Publication date: Available online 13 May 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Mohamed Amine Sobhi, Li Li Backfill is commonly used in underground mines to help to increase the ore recovery rate and reduce the ore dilution. The use of a part of mine waste as underground backfill material also helps to reduce the environmental impact of mining operations. After all, backfill is used to provide a working platform or safer working space. Its primary and most important role is to improve the rock mass stability around mine openings. However, most available solutions to stress analyses were developed for an isolated stope, without taking into account the influence of mine depth, or of adjacent stopes. In this paper, results from a numerical study carried out to evaluate the stresses in backfilled stopes overlying a sill mat are presented. Mine depth and excavation of the underlying stope below the sill mat (horizontal pillar) are both taken into consideration. The influence of stope geometry, backfill, sill mat and rock properties on the stresses is also evaluated. Compared with the case of a single isolated backfilled stope, the numerical results show that the stress magnitudes in the overlying backfill are considerably increased due to the excavation of the underlying stope. In general, the stresses also increase with mine depth and backfill stiffness, while these tend to decrease with an increase in the surrounding rock mass stiffness. These results suggest that existing solutions for backfill design may need to be revised.

Description: Publication date: Available online 3 May 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Charlie C. Li Abstract This article introduces the principles of underground rockbolting design. The items discussed include underground loading conditions, natural pressure zone around an underground opening, design methodologies, selection of rockbolt types, determination of bolt length and spacing, factor of safety, and compatibility between support elements. Different types of rockbolting used in engineering practise are also presented. The traditional principle of selecting strong rockbolts is valid only in conditions of low in situ stresses in the rock mass. Energy-absorbing rockbolts are preferred in the case of high in situ stresses. A natural pressure arch is formed in the rock at a certain distance behind tunnel wall. Rockbolts should be long enough to reach the natural pressure arch when the failure zone is small. The bolt length should be at least 1 m beyond the failure zone. In the case of a vast failure zone, tightly spaced short rockbolts are installed to establish an artificial pressure arch within the failure zone and long cables are anchored on the natural pressure arch. In this case, the rockbolts are usually less than 3 m long in mine drifts, but can be up to 7 m in large-scale rock caverns. Bolt spacing is more important than bolt length in the case of establishing an artificial pressure arch. In addition to the factor of safety, the maximum allowable displacement in the tunnel and the ultimate displacement capacity of rockbolts must be also taken into account in the design. Finally, rockbolts should be compatible with other support elements in the same support system in terms of displacement and energy absorption capacities.

Description: Publication date: Available online 23 April 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Y. Jia, H.B. Bian, G. Duveau, J.F. Shao In this paper, the thermo-hydro-mechanical (THM) response of claystone is studied via a series of parametric studies, considering the evolution of mechanical properties and deformation behavior of corroded steel. The numerical simulations are performed by using a coupled THM finite element code and two different constitutive models: a visco-elastoplastic model for geological formation and a von Mises type model for steel liner. The mechanical properties and deformation behavior of corroded steel are described in a conceptual model. Finally, a disposal tunnel supported by a steel liner is studied and a series of parametric studies is defined to demonstrate the corrosion effects of steel liner on the THM response of the claystone. The comparison of different numerical calculations exhibits that the volumetric expansion related to corrosion products has an important impact on the stress and displacement fields in the claystone surrounding the disposal tunnel. However, the evolutions of temperature and liquid pressure in the claystone are essentially controlled by its THM properties and independent of the steel corrosion.

Description: Publication date: Available online 21 April 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): W.Z. Chen, Y.S. Ma, H.D. Yu, F.F. Li, X.L. Li, X. Sillen Boom Clay is one of the potential host rocks for deep geological disposal of high-level radioactive nuclear waste in Belgium. In order to investigate the mechanism of hydraulic conductivity variation under complex thermo-mechanical coupling conditions and to better understand the thermo-hydro-mechanical (THM) coupling behaviour of Boom Clay, a series of permeability tests using temperature-controlled triaxial cell has been carried out on the Boom Clay samples taken from Belgian underground research laboratory (URL) HADES. Due to its sedimentary nature, Boom Clay presents across-anisotropy with respect to its sub-horizontal bedding plane. Direct measurements of the vertical ( K v ) and horizontal ( K h ) hydraulic conductivities show that the hydraulic conductivity at 80 °C is about 2.4 times larger than that at room temperature (23 °C), and the hydraulic conductivity variation with temperature is basically reversible during heating-cooling cycle. The anisotropic property of Boom Clay is studied by scanning electron microscope (SEM) tests, which highlight the transversely isotropic characteristics of intact Boom Clay. It is shown that the sub-horizontal bedding feature accounts for the horizontal permeability higher than the vertical one. The measured increment in hydraulic conductivity with temperature is lower than the calculated one when merely considering the changes in water kinematic viscosity and density with temperature. The nuclear magnetic resonance (NMR) tests have also been carried out to investigate the impact of microstructure variation on the THM properties of clay. The results show that heating under unconstrained boundary condition will produce larger size of pores and weaken the microstructure. The discrepancy between the hydraulic conductivity experimentally measured and predicted (considering water viscosity and density changes with temperature) can be attributed to the microstructural weakening effect on the thermal volume change behaviour of Boom Clay. Based on the experimental results, a hydraulic conductivity evolution model is proposed and then implemented in ABAQUS. Three-dimensional (3D) numerical simulation of the admissible thermal loading for argillaceous storage (ATLAS) III in situ heating test has been conducted subsequently, and the numerical results are in good agreement with field measurements.

Description: Publication date: Available online 6 March 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): E.T. Brown

Description: Publication date: Available online 6 March 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Yanjun Shang, Lihui Li, Wantong He, Luqing Zhang, Tianbin Li, Zhifa Yang Long-term stability of large-span caverns is a challenging issue for design and construction of underground rock engineering. The Heidong cavern group consisting of 21 caverns was constructed about 1400 years ago for quarrying in massive Cretaceous tuff. The cavern No. 5 of the Heidong cavern group is characterized by an unsupported span up to 92 m, with the overburden thickness of only 3–25 m. To analyze its long-term stability, a detailed investigation was conducted to obtain its geometry and rock mass characteristics, and to monitor surrounding rock displacements. Based on field survey and laboratory tests, numerical simulations were performed using the finite difference code FLAC 3D . The analysis results revealed that for the long-term stability of the cavern No. 5, some major factors should be carefully considered, such as cavern excavation method in hard massive rocks, site investigation using trial pits, tools like short iron chisel and hammer for manual excavation, geometric dome roof, and waste rocks within abutment or on the floor. The highlights of the technologies obtained from this large-scale ancient underground project can provide reference for other similar project excavations in practice.

Description: Publication date: Available online 10 March 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): François Bertrand, Frédéric Collin Deep repository in geological formations is the preferential solution considered by many countries to manage high-level nuclear wastes. In Switzerland, the Opalinus Clay is a candidate host rock. In this context, in situ and laboratory tests are conducted on Opalinus Clay to demonstrate the feasibility of deep disposal in this argillaceous formation. This paper presents a constitutive model able to fit the experimental data obtained from some triaxial tests conducted by Jahns [1] on cores from bore hole Schlattingen SLA-1. The elasto-plastic behaviour of Opalinus Clay is reproduced thanks to a Drucker-Prager model, taking into account the anisotropy behaviour of this sedimentary rock. The objective is to employ a single set of parameters representative of the material. In a second version of the model, the stress-dependency of the elastic properties and damage are taken into account. Finally, the parameters calibrated with experimental tests are used to simulate the excavation of a gallery with a second gradient approach.

Description: Publication date: Available online 29 April 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Paul Bossart, David Jaeggi, Christophe Nussbaum Repositories for deep geological disposal of radioactive waste rely on multi-barrier systems to isolate waste from the biosphere. A multi-barrier system typically comprises the natural geological barrier provided by the repository host rock – in our case the Opalinus clay – and an engineered barrier system (EBS). The Swiss repository concept for spent fuel and vitrified high-level waste (HLW) consists of waste canisters, which are emplaced horizontally in the middle of an emplacement gallery and are separated from the gallery wall by granular backfill material (GBM). We describe here a selection of five in-situ experiments where we have observed characteristic hydro-mechanical (HM) and thermo-hydro-mechanical (THM) processes. The first example is a coupled HM) and mine-by test where the evolution of the excavation damaged zone (EDZ) was monitored around a gallery in the Opalinus clay (ED-B experiment). Measurements of pore-water pressures and convergences due to stress redistribution during excavation highlighted the HM behaviour. The same measurements were subsequently carried out in a heater test (HE-D) where we were able to characterise the Opalinus clay in terms of its THM behaviour. These yielded detailed data to better understand the THM behaviour of the granular backfill and the natural host rock. For a presentation of the Swiss concept for HLW storage, we designed three demonstration experiments that were subsequently implemented in the Mont Terri rock laboratory: (1) the engineered barrier (EB) experiment, (2) the in-situ heater test on key-THM processes and parameters HE-E (HE-E) experiment, and (3) the full-scale emplacement (FE) experiment. The first demonstration experiment has been dismantled, but the last two ones are on-going.

Description: Publication date: Available online 4 May 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Y.M. Alshkane, A.M. Marshall, L.R. Stace The accurate prediction of strength and deformability characteristics of rock mass is a challenging issue. In practice, properties of a rock mass are often estimated from available empirical relationships based on the uniaxial compressive strength (UCS). However, UCS does not always give a good indication of in situ rock mass strength and deformability. The aim of this paper is to present a methodology to predict the strength and deformability of a jointed rock mass using UDEC (universal distinct element code). In the study, the rock mass is modelled as an assemblage of deformable blocks that can yield as an intact material and/or slide along predefined joints within the rock mass. A range of numerical simulations of uniaxial and triaxial tests was conducted on rock mass samples in order to predict the equivalent mechanical properties for the rock mass under different loading directions. Finally, results are compared with the deformability parameters obtained by analytical methods.

Description: Publication date: Available online 4 May 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Danièle Bartier, Christophe Auvray Micro-mechanical properties of a claystone were tested after undergoing alkaline perturbation on site (Tournemire, CD borehole) for 18 years. In a saturated context and outside the excavation disturbed zone (EDZ), the claystone exhibits a 11.6-mm black rim at the cement/paste interface, which shows a different mechanical behaviour from the rest of the claystone. Three sets of measurements of elastic modulus were performed using: (i) nano-indentation tests with a constant indentation depth of 2 μm, (ii) micro-indentation tests with a constant indentation depth of 20 μm, and (iii) meso-compression tests with a constant displacement of 200 μm. The increase of the modulus of deformability in the black rim is between 15 GPa and 20 GPa according to the scale. Moreover, an overall decrease of the modulus of deformability from the smallest to the largest scale is observed in each zone. In view of the mineralogy and petrographic observations, higher values of modulus of deformability in the black rim are related to carbonate content and its distribution. Precipitation of cementitious carbonates as inclusions and very thin partings leads to hardening of the claystone.

Description: Publication date: Available online 4 May 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Katrin M. Wild, Marco Barla, Giovanni Turinetti, Florian Amann In many engineering applications, it is important to determine both effective rock properties and the rock behavior which are representative for the problem’s in situ conditions. For this purpose, rock samples are usually extracted from the ground and brought to the laboratory to perform laboratory experiments such as consolidated undrained (CU) triaxial tests. For low permeable geomaterials such as clay shales, core extraction, handling, storage, and specimen preparation can lead to a reduction in the degree of saturation and the effective stress state in the specimen prior to testing remains uncertain. Related changes in structure and the effect of capillary pressure can alter the properties of the specimen and affect the reliability of the test results. A careful testing procedure including back-saturation, consolidation and adequate shearing of the specimen, however, can overcome these issues. Although substantial effort has been devoted during the past decades to the establishment of a testing procedure for low permeable geomaterials, no consistent protocol can be found. With a special focus on CU tests on Opalinus Clay, this study gives a review of the theoretical concepts necessary for planning and validating the results during the individual testing stages (saturation, consolidation, and shearing). The discussed tests protocol is further applied to a series of specimens of Opalinus Clay to illustrate its applicability and highlight the key aspects.

Description: Publication date: Available online 3 May 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Seyed Mahmoud Anvari, Issa Shooshpasha, Saman Soleimani Kutanaei Review of the literature relating to the mixture of tire shredded and sand shows that, despite of increase in shear strength due to addition of tire chips, granulated rubber causes reduction in shear strength of sand. In this study, shear behavior of mixtures of fine-grained sand and 1 to 5-mm granulated rubber is investigated. For this purpose, 60 direct shear tests were conducted on sand-granulated rubber mixtures having various percentages of rubber (0, 5, 10, 20, and 30) at different relative densities (50, 70 and 90%) and tested at different normal pressures of (34.5, 54.5, 74.5 and 104.5 kPa). According to achieved results, granulated rubber improves shear strength of fine-grained sand at medium density and low normal pressure. The degree of improvement in shear strength is function of rubber content, density and normal stress. The results show that, at relative density of 50%, by increasing 5% granulated rubber, the friction angle of sand increases from 35.1˚ to 39.2˚. However, at relative densities of 70% and 90%, addition of granulated rubber to sand decreases its friction angle value. Moreover, the results indicate that behavior of sand becomes more ductile with increasing granulated rubber content. Adding granulated rubber leads sand to have more capacity in yielding strain and less tangent stiffness. The maximum dilatancy angle decreased with the decreased in percentage of granulated rubber. The stress ratio of sample at critical state () decrease with increasing the granulated rubber content.

Description: Publication date: Available online 15 April 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Frédéric Bernier, Frank Lemy, Pierre De Cannière, Valéry Detilleux The mission of nuclear safety authorities in national radioactive waste disposal programmes is to ensure that people and the environment are protected against the hazards of ionising radiations emitted by the waste. It implies the establishment of safety requirements and the oversight of the activities of the waste management organisation in charge of implementing the programme. In Belgium, the safety requirements for geological disposal rest on the following principles: defence-in-depth, demonstrability and the radiation protection principles elaborated by the International Commission on Radiological Protection (ICRP). Applying these principles requires notably an appropriate identification and characterisation of the processes upon which the safety functions fulfilled by the disposal system rely and of the processes that may affect the system performance. Therefore, research and development (R&D) on safety-relevant thermo-hydro-mechanical-chemical (THMC) issues is important to build confidence in the safety assessment. This paper points out the key THMC processes that might influence radionuclide transport in a disposal system and its surrounding environment, considering the dynamic nature of these processes. Their nature and significance are expected to change according to prevailing internal and external conditions, which evolve from the repository construction phase to the whole heating-cooling cycle of decaying waste after closure. As these processes have a potential impact on safety, it is essential to identify and to understand them properly when developing a disposal concept to ensure compliance with relevant safety requirements. In particular, the investigation of THMC processes is needed to manage uncertainties. This includes the identification and characterisation of uncertainties as well as for the understanding of their safety-relevance. R&D may also be necessary to reduce uncertainties of which the magnitude does not allow demonstrating the safety of the disposal system.

Description: Publication date: Available online 1 February 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Mohammad Rashidi, S.Mohsen Haeri In this study, the behavior of Gavoshan dam was evaluated during construction, and at the time of the first impounding. A two-dimensional numerical analysis was conducted based on a finite difference method on the largest cross-section of the dam through using the results of instrument measurements and back analysis. These evaluations will be completed in case back analysis is carried out in order to control the degree of the accuracy and the level of confidence of the measured behavior since each of the measurements could be controlled through comparing it to the model obtained from the numerical model. Following that, comparing the results of the numerical analysis with the measured values, indicates that there is a proper consistency between these two values. Moreover it was observed that the dam’s performance was suitable regarding the created pore water pressure, pore water pressure ratio r u , settlement, the created stresses, the arching degree, and hydraulic fracturing probability in the construction period as well as during the first impounding. The results demonstrated that the maximum settlement of the core was 238 centimeters at the end of construction. In the following 6 years after construction (initial impounding and exploitation period) the accumulative settlement of the dam was 270 centimeters. It is clear that 88% of the total settlement of the dam took place during dam construction and the reason is the clay core being smashed in the wet side, optimum moisture content. In addition, whereas the average of curving ratio was 0.64 during dam construction, At the end of the initial impounding, the maximum amount of curving ratio in the upstream was 0.81 and the minimum and its critical amount in the downstream was 0.52. It was also concluded that this dam is secure in comparison with the behavior of other similar dams in the world.

Description: Publication date: Available online 15 April 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Gongda Lu, Mamadou Fall, Liang Cui Although a large number of previous researches have significantly contributed to the understanding of the quasi-static mechanical behavior of cemented tailings backfill, an evolutive porous medium used in underground mine cavities, very few efforts have been made to improve the knowledge on its response under sudden dynamic loading during the curing process. In fact, there is a great need for such information given that cemented backfill structures are often subjected to blast loadings due to mine exploitations. In this study, a coupled thermo-hydro-mechanical-chemical (THMC)-viscoplastic cap model is developed to describe the behavior of cementing mine backfill material under blast loading. A THMC model for cemented backfill is adopted to evaluate its behavior and evolution of its properties in curing processes with coupled thermal, hydraulic, mechanical and chemical factors. Then, the model is coupled to a Perzyna type of viscoplastic model with a modified smooth surface cap envelope and a variable bulk modulus, in order to reasonably capture the nonlinear and rate-dependent behaviors of the cemented tailings backfill under blast loading. All of the parameters required for the variable-modulus viscoplastic cap model were obtained by applying the THMC model to reproducing evolution of cemented paste backfill (CPB) properties in the curing process. Thus, the behavior of hydrating cemented backfill under high-rate impacts can be evaluated under any curing time of concern. The validation results of the proposed model indicate a good agreement between the experimental and the simulated results. The authors believe that the proposed model will contribute to a better understanding of the performance of hydrating cemented backfill under blasting, and also to practical risk management of backfill structures associated with such a dynamic condition.

Description: Publication date: Available online 15 April 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Aram M. Raheem, Cumaraswamy Vipulanandan, Mohammad S. Joshaghani The characterization of ultra-soft clayey soil exhibits extreme challenges due to low shear strength of such material. Hence, inspecting the non-destructive electrical impedance behavior of untreated and treated ultra-soft clayey soils gains more attention. Both shear strength and electrical impedance were measured experimentally for both untreated and treated ultra-soft clayey soils. The shear strength of untreated ultra-soft clayey soil reached 0.17 kPa for 10% bentonite content, while the shear strengths increased to 0.27 kPa and 6.7 kPa for 10% bentonite content treated with 2% lime and 10% polymer, respectively. The electrical impedance of the ultra-soft clayey soil has shown a significant decrease from 1.6 kΩ to 0.607 kΩ when the bentonite content increased from 2% to 10% at a frequency of 300 kHz. The 10% lime and 10% polymer treatments have decreased the electrical impedances of ultra-soft clayey soil with 10% bentonite from 0.607 kΩ to 0.12 kΩ and 0.176 kΩ, respectively, at a frequency of 300 kHz. A new mathematical model has been accordingly proposed to model the non-destructive electrical impedance-frequency relationship for both untreated and treated ultra-soft clayey soils. The new model has shown a good agreement with experimental data with coefficient of determination ( R 2 ) up to 0.99 and root mean square error ( RMSE ) of 0.007 kΩ.

Description: Publication date: Available online 31 March 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Jingjin Liu, Huayang Lei, Gang Zheng, Haizuo Zhou, Xuelian Zhang Problems continue to be disseminated concerning the traditional vacuum preloading method in the real fields during the treatment of newly dredger fill deposits. In this paper, an improved multiple-vacuum preloading method was developed to consolidate newly dredger fills that is hydraulically placed in seawater for land reclamation in Lin Gang Industrial Zone of Tianjin City, China. With this multiple-vacuum preloading method, the newly dredger fills could be processed effectively by adopting a novel moisture separator and a rapid improvement technique without sand cushion. A series of parallel model tests were conducted in the laboratory for comparing the results of different kinds of multiple-vacuum preloading methods and the traditional one. Tens of piezometers and settlement plates were installed to measure the variations of excess pore water pressures and the moisture content and van shear strength observation points at different positions. The testing results indicate that water discharge-time relationship curves in the traditional vacuum preloading method are divided into three phases: the rapid growth phase, slow growth phase and steady phase. According to the process of fluid flow focus along tiny ripples and build bigger channels inside soils during the whole vacuum loading process, the fluctuations of pore water pressure during each loading steps are divided into three phases: steady phase, rapid dissipation phase, and slow dissipation phase. An optimal loading pattern which could have a best treatment effect is proposed for calculating water discharge and pore water pressure of the soil induced by improved multiple-vacuum preloading method. For newly dredger fills from Lin Gang Industrial Zone, 20 kPa is the best loading spacing and step with 40 kPa∼50 kPa loading value has the highest drainage consolidation. The measured moisture content and vane shear strength values are discussed as the effect of reinforcement which both indicate that the multiple-vacuum preloading method has a better treatment effect not only in decreasing the moisture content and increasing the bearing capacity, but also in increasing the process uniformity at different depth of the foundation.

Description: Publication date: Available online 6 April 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): G. Armand, F. Bumbieler, N. Conil, R. de la Vaissière, J.-M. Bosgiraud, M.-N. Vu In the context of radioactive waste disposal, an underground research laboratory (URL) is a facility in which experiments are conducted so as to demonstrate the feasibility of constructing and operating a radioactive waste disposal facility within a geological formation. The Meuse/Haute-Marne URL is a site-specific facility planned to study the feasibility of a radioactive waste disposal in the Callovo-Oxfordian (COx) claystone. The thermo hydro mechanical (THM) behaviour of the host rock is significant for the design of the underground nuclear waste disposal facility and for its long-term safety. The French National Radioactive Waste Management Agency (Andra) has begun a research programme aiming to demonstrate the relevancy of the French high-level waste concept. This paper presents the programme implemented from small-scale (small diameter) boreholes to full scale demonstration experiments to study the THM effects of the thermal transient on the COx claystone and the strategy implemented in this new programme to demonstrate and optimize current disposal facility components for high-level waste. It shows that the French high level waste concept is feasible and working in the COx claystone. It also exhibits that, as for other plastic clay or claystone, heating induce pore pressure increase and that the THM behavior is anisotropic.

Description: Publication date: Available online 6 April 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Mohammad Reza Azadi, Ali Taheri, Ali Taghichian Grout injection is used for sealing or strengthening the ground in order to prevent water entrance or any failure after excavation. There are many methods of grouting. Permeation grouting is one of the most common types in which the grout material is injected to the pore spaces of the ground. In grouting operations, the grout quality is important to achieve the best results. There are four main characteristics for a grout mixture including bleeding, setting time, strength, and viscosity. In this paper, we try to build some efficient grouting mixtures with different water to cement ratios considering these characteristics. The ingredients of grout mixtures built in this study are cement, water, bentonite, and some chemical additives such as sodium silicate, sodium carbonate, and triethanolamine (TEA). The grout mixtures are prepared for both of the sealing and strengthening purposes for a structural project. Effect of each above-mentioned ingredient is profoundly investigated. Since each ingredient may have positive or negative aspect, an optimization of appropriate amount of each ingredient is determined. The optimization is based on 200 grout mixture samples with different percentages of ingredients. Finally, some of these grout mixtures are chosen for the introduced project. It should be mentioned that grouting operations depend on various factors such as pressure of injection, ground structure and grain size of soils. However, quality of a grout can be helpful to make an injection easier and reasonable. For example, during the injection, a wrong estimated setting time can destroy the injected grout by washing the grout or setting early which prevents grouting. This paper tries to show some tests in easy way to achieve a desirable sample of grout.

Description: Publication date: Available online 19 January 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Gioacchino Francesco Andriani, Mario Parise Classical rock mass classification systems are not applicable to carbonate rocks, especially when these are affected by karst processes. Their applications to such settings could therefore result in outcomes not representative of the real stress-strain behavior. In this study, we propose a new classification of carbonate rock masses for engineering purposes, by adapting the rock engineering system (RES) method by Hudson for fractured and karstified rock masses, in order to highlight the problems of implementation of geomechanical models to carbonate rocks. This new approach allows a less rigid classification for carbonate rock masses, taking into account the local properties of the outcrops, the site conditions and the type of engineering work as well.

Description: Publication date: Available online 27 February 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): R.A.T.M. Ranasinghe, M.B. Jaksa, Y.L. Kuo, F. Pooya Nejad Rolling dynamic compaction (RDC), which involves the towing of a noncircular module, is now widespread and accepted among many other soil compaction methods. However, to date, there is no accurate method for reliable prediction of the densification of soil and the extent of ground improvement by means of RDC. This study presents the application of artificial neural networks (ANNs) for a priori prediction of the effectiveness of RDC. The models are trained with in situ dynamic cone penetration (DCP) test data obtained from previous civil projects associated with the 4-sided impact roller. The predictions from the ANN models are in good agreement with the measured field data, as indicated by the model correlation coefficient of approximately 0.8. It is concluded that the ANN models developed in this study can be successfully employed to provide more accurate prediction of the performance of the RDC on a range of soil types. Graphical abstract

Description: Publication date: Available online 21 February 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): G. Bella, M. Barbero, F. Barpi, M. Borri-Brunetto, D. Peila The paper presents a new prefabricated bio-engineering structure for the support of unstable soil. This prefabricated structure is made of a steel frame which is completely filled with soil and a face made of tree trunks among which scions or autochthonous bushes are planted. Due to the difficulties in interpreting the complex interaction between soil and structure during the installation and lifetime, an in situ test was carried out in order to evaluate the state of stress in the steel frame and to understand the global behavior of the structure under service loads. On the basis of the obtained results, a procedure for checking the structure safety was proposed and discussed. An easy design method was developed during the research. Moreover, the use of this type of prefabricated structure shows several advantages, such as good performances in terms of stabilizing effects, and easy assembly and transport.

Description: Publication date: Available online 26 November 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Hassan Basahel, Hani Mitri The stability of rock slopes is considered crucial to public safety in highways passing through rock cuts, as well as to personnel and equipment safety in open pit mines. Slope instability and failures occur due to many factors such as adverse slope geometries, geological discontinuities, weak or weathered slope materials as well as severe weather conditions. External loads like heavy precipitation and seismicity could play a significant role in slope failure. In this paper, several rock mass classification systems developed for rock slope stability assessment are evaluated against known rock slope conditions in a region of Saudi Arabia, where slopes located in rugged terrains with complex geometry serve as highway road cuts. Selected empirical methods have been applied to 22 rock cuts that are selected based on their failure mechanisms and slope materials. The stability conditions are identified, and the results of each rock slope classification system are compared. The paper also highlights the limitations of the empirical classification methods used in the study and proposes future research directions.

Description: Publication date: Available online 21 November 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Shahé Shnorhokian, Bryce MacNeil, Hani S. Mitri Haulage networks are vital to underground mining operations as they constitute the arteries through which blasted ore is transported to surface. In the sublevel stoping method and its variations, haulage drifts are excavated in advance near the ore block that will be mined out. Numerical modelling is a technique that is frequently employed to assess the redistribution of mining-induced stresses, and to compare the impact of different stope sequence scenarios on haulage network stability. In this study, typical geological settings in the Canadian Shield were replicated in a numerical model with a steeply-dipping tabular orebody striking EW. All other formations trended in the same direction except for two dykes on either side of the orebody with a WNW-ESE strike. Rock mass properties and in situ stress measurements from a case study mine were used to calibrate the model. Drifts and crosscuts were excavated in the footwall and two stope sequence scenarios – a diminishing pillar and a center-out one – were implemented in 24 mining stages. A combined volumetric-numerical analysis was conducted for two active levels by comparing the extent of unstable rock mass at each stage using shear, compressive, and tensile instability criteria. Comparisons were made between the orebody and the host rock, between the footwall and hanging wall, and between the two stope sequence scenarios. It was determined that in general, the center-out option provided a larger volume of instability with the shear criterion when compared to the diminishing pillar one (625,477 m 3 compared to 586,774 m 3 in the orebody; 588 m 3 compared to 403 m 3 in the host rock). However, the reverse was true for tensile (134,298 m 3 compared to 128,834 m 3 in the orebody; 91,347 m 3 compared to 67,655 m 3 in the host rock) instability where the diminishing pillar option had the more voluminous share.

Description: Publication date: Available online 3 November 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Georgia S. Araujo, Kátia V. Bicalho, Fernando A. Tristão The particle morphology and surface texture play a major role in influencing mechanical and hydraulic behaviors of sandy soils. This paper presents the use of digital image analysis combined with fractal theory as a tool to quantify the particle morphology and surface texture of two types of quartz sands widely used in the region of Vitória, Espírito Santo, southeast of Brazil. The two investigated sands are sampled from different locations. The purpose of this paper is to present a simple, straightforward, reliable and reproducible methodology that can identify representative sandy soil texture parameters. The test results of the soil samples of the two sands separated by sieving into six size fractions are presented and discussed. The main advantages of the adopted methodology are its simplicity, reliability of the results, and relatively low cost. The results show that sands from the coastal spit (BS) have a greater degree of roundness and a smoother surface texture than river sands (RS). The values obtained in the test are statistically analyzed, and again it is confirmed that the BS sand has a slightly greater degree of sphericity than that of the RS sand. Moreover, the RS sand with rough surface texture has larger specific surface area values than the similar BS sand, which agree with the obtained roughness fractal dimensions. The consistent experimental results demonstrate that image analysis combined with fractal theory is an accurate and efficient method to quantify the differences in particle morphology and surface texture of quartz sands.

Description: Publication date: Available online 10 November 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Rohola Hasanpour, Jürgen Schmitt, Yilmaz Ozcelik, Jamal Rostami Severe shield jamming events have been reported during excavation of Uluabat tunnel through adverse geological conditions, which resulted in several stoppages at advancing a single shielded tunnel boring machine (TBM). To study the jamming mechanism, three-dimensional (3D) simulation of the machine and surrounding ground was implemented using the finite difference code FLAC3D. Numerical analyses were performed for three sections along the tunnel with a higher risk for entrapment due to the combination of overburden and geological conditions. The computational results including longitudinal displacement contours and ground pressure profiles around the shield allow a better understanding of ground behavior within the excavation. Furthermore, they allow realistically assessing the impact of adverse geological conditions on shield jamming. The calculated thrust forces, which are required to move the machine forward, are in good agreement with field observations and measurements. It also proves that the numerical analysis can effectively be used for evaluating the effect of adverse geological environment on TBM entrapments and can be applied to prediction of loads on the shield and pre-estimating of the required thrust force during excavation through adverse ground conditions.

Description: Publication date: Available online 23 November 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Jie Li, Mingyang Wang, Kaiwen Xia, Ning Zhang, Houxu Huang This paper presents a theoretical study on time-dependent dilatancy behaviors for brittle rocks. The theory employs a well-accepted postulation that macroscopically observed dilatancy originates from the expansion of microcracks. The mechanism and dynamic process that microcracks initiate from local stress concentration and grow due to localized tensile stress are analyzed. Then, by generalizing the results from the analysis of single cracks, a parameter and associated equations for its evolution are developed to describe the behaviors of the microcracks. In this circumstance, the relationship between microcracking and dilatancy can be established, and the theoretical equations for characterizing the process of rock dilatancy behaviors are derived. Triaxial compression and creep tests are conducted to validate the developed theory. With properly chosen model parameters, the theory yields a satisfactory accuracy in comparison with the experimental results.

Description: Publication date: Available online 26 November 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Huan He, Mingnan Li, Kostas Senetakis In this study, extender and bender element tests were conducted investigating the small-strain Poisson's ratio of variable sands, with a focus on the effect of stress anisotropy in order to quantify the sensitivity of Poisson's ratio to the applied deviatoric stress. Four different uniform sands were tested, including a biogenic sand, a crushed rock and two natural sands, covering a wide range of particle shapes. From these sands, eleven samples were prepared in the laboratory and were tested under variable stress paths, maintaining a constant mean effective pressure while increasing the deviatoric compressive load. Under the application of these given stress paths, the data analysis indicated that the sensitivity of Poisson's ratio to the stress ratio was more pronounced for sands with irregularly shaped particles in comparison to sands with fairly rounded and spherical grains. For sands with very irregularly shaped particles, the increase of Poisson's ratio from the isotropic to the anisotropic stress state reached 50%, while this increase for natural sands with fairly rounded particles was in the order of 20%.

Description: Publication date: Available online 21 November 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Chhatra Bahadur Basnet, Krishna Kanta Panthi Abstract Most of the existing roughness estimation methods for water tunnels are related to either unlined or concrete/steel-lined tunnels. With the improvement in shotcrete technology, advancement in tunneling equipment and cost and time effectiveness, future water tunnels built for hydropower projects will consist of rock support with the extensive use of shotcrete lining in combination with systematic bolting and concrete lining in the tunnel invert. However, very little research has been performed to find out tunnel surface roughness for shotcrete-lined tunnels with invert concrete, which is important in calculating overall head loss along the waterway system to achieve an optimum and economic hydropower plant design. Hence, the main aim of this article is to review prevailing methods available to calculate tunnel wall roughness, and to use existing methods of head loss calculation to back-calculate roughness of the shotcrete-lined tunnels with invert concrete by exploiting measured head loss and actual cross-sectional profiles of two headrace tunnels from Nepal. Furthermore, the article aims to establish a link between the Manning coefficient and the physical roughness of the shotcrete-lined tunnel with invert concrete and to establish a link between over-break thickness and physical roughness. Attempts are also made to find a correlation between over-break thickness and rock mass quality described by Q-system and discussions are conducted on the potential cost savings that can be made if concrete lining is replaced by shotcrete lining with invert concrete.

Description: Publication date: Available online 4 July 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Mohammad Saberian, Soheil Jahandari, Jie Li, Farzad Zivari Lime concrete and lime treatment are two attractive techniques for geotechnical engineers. However, researches have rarely been carried out to study the effects of moisture and capillary action due to increasing groundwater level on geotechnical properties of lime concrete. The aim of this study is to investigate the effects of curing time and degree of saturation on some of geotechnical properties of lime concrete such as unconfined compressive strength (UCS), secant modulus ( E s ), failure strain, brittleness index ( I B ), and deformability index ( I D ) using unconfined compression tests. First of all, geotechnical and chemical properties of used materials were determined. After curing times of 14 d, 28 d, 45 d, and 60 d in laboratory condition, the specimens were exposed to saturation levels ranging from 0 to 100%. The results showed that the moisture and curing time have significant effects on the properties of lime concrete. Based on the results of scanning electron micrograph (SEM) test, it was observed that the specimen was characterized by a rather well-structured matrix since both the filling of a large proportion of the coarse-grained soil voids by clay and the pozzolanic activity of lime led to retaining less pore water in the specimen, increasing the UCS and E s , and consequently resisting against swelling and shrinkage of the clay soil. Moreover, due to the pozzolanic reactions and reduction of water, by increasing the curing time and decreasing the degrees of saturation, UCS, E s , and I B increased, and I D decreased. Based on the experimental results, a phenomenological model was used to develop equations for predicting the properties in relation to the ratio of degree of saturation/curing time. The results showed that there was a good correlation (almost R 2 > 90%) between the measured parameters and the estimated ones given by the predicted equations.

Description: Publication date: Available online 10 July 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Kunui Hong, Eunchol Han, Kwangsong Kang The geological strength index (GSI) system, widely used for the design and practice of mining process, is a unique rock mass classification system related to the rock mass strength and deformation parameters based on the generalized Hoek-Brown and Mohr-Coulomb failure criteria. The GSI can be estimated using standard chart and field observations of rock mass blockiness and discontinuity surface conditions. The GSI value gives a numerical representation of the overall geotechnical quality of the rock mass. In this study, we propose a method to determine the GSI quantitatively using photographic images of in situ jointed rock mass with image processing technology, fractal theory and artificial neural network (ANN). We employ the GSI system to characterize the jointed rock mass around the working in a coal mine. The relative error between the proposed value and the given value in the GSI chart is less than 3.6%.

Description: Publication date: Available online 10 July 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Simon Heru Prassetyo, Marte Gutierrez, Nick Barton Experiments on rock joint behaviors have shown that joint surface roughness is mobilized under shearing, inducing dilation and resulting in nonlinear joint shear strength and shear stress vs. shear displacement behaviors. The Barton-Bandis (B-B) joint model provides the most realistic prediction for the nonlinear shear behavior of rock joints. The B-B model accounts for asperity roughness and strength through the joint roughness coefficient ( JRC ) and joint wall compressive strength ( JCS ) parameters. Nevertheless, many computer codes for rock engineering analysis still use the constant shear strength parameters from the linear Mohr-Coulomb (M-C) model, which is only appropriate for smooth and non-dilatant joints. This limitation prevents fractured rock models from capturing the nonlinearity of joint shear behavior. To bridge the B-B and the M-C models, this paper aims to provide a linearized implementation of the B-B model using a tangential technique to obtain the equivalent M-C parameters that can satisfy the nonlinear shear behavior of rock joints. These equivalent parameters, namely the equivalent peak cohesion, friction angle, and dilation angle, are then converted into their mobilized forms to account for the mobilization and degradation of JRC under shearing. The conversion is done by expressing JRC in the equivalent peak parameters as functions of joint shear displacement using proposed hyperbolic and logarithmic functions at the pre- and post-peak regions of shear displacement, respectively. Likewise, the pre- and post-peak joint shear stiffnesses are derived so that a complete shear stress-shear displacement relationship can be established. Verifications of the linearized implementation of the B-B model show that the shear stress-shear displacement curves, the dilation behavior, and the shear strength envelopes of rock joints are consistent with available experimental and numerical results.

Description: Publication date: Available online 10 July 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): H. Munoz, A. Taheri The complete stress-strain characteristics of sandstone specimens were investigated in a series of quasi-static monotonic uniaxial compression tests. Strain patterns development during pre- and post-peak behaviours in specimens with different aspect ratios was also examined. Peak stress, post-peak portion of stress-strain, brittleness, characteristics of progressive localisation and field strain patterns development were affected at different extents by specimen aspect ratio. Strain patterns of the rocks were obtained by applying three-dimensional (3D) digital image correlation (DIC) technique. Unlike conventional strain measurement using strain gauges attached to specimen, 3D DIC allowed not only measuring large strains, but more importantly, mapping the development of field strain throughout the compression test, i.e. in pre- and post-peak regimes. Field strain development in the surface of rock specimen suggests that strain starts localising progressively and develops at a lower rate in pre-peak regime. However, in post-peak regime, strains increase at different rates as local deformations take place at different extents in the vicinity and outside the localised zone. The extent of localised strains together with the rate of strain localisation is associated with the increase in rate of strength degradation. Strain localisation and local inelastic unloading outside the localised zone both feature post-peak regime.

Description: Publication date: Available online 17 July 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Ali Noorzad, Ehsan Badakhshan Experimental and numerical investigations have been carried out on behavior of pullout resistance of embedded circular plate with and without geogrid reinforcement layers in stabilized loose and dense sands using a granular trench. Different parameters have been considered, such as the number of geogrid layers, embedment depth ratio, relative density of soil and height ratio of granular trench. Results showed that, without granular trench, the single layer of geogrid was more effective in enhancing the pullout capacity compared to the multilayer of geogrid reinforcement. Also, increasing the soil density and embedment depth ratio led to an increase in the uplift capacity. When soil was improved with the granular trench, the uplift force significantly increased. The granular trench improved the uplift load in dense sand more, as compared to the same symmetrical plate embedded in loose sand. Although it was observed that, in geogrid-reinforced granular trench condition, the ultimate pullout resistance at failure increased as the number of geogrid layers increased up to the third layer, and the fifth layer had a negligible effect in comparison with the third layer of reinforcement. Finite element analyses with hardening soil model for sand and CANAsand constitutive model for granular trench were conducted to investigate the failure mechanism and the associated rupture surfaces utilized. The response of granular material in the proposed model is an elastoplastic constitutive model derived from the CANAsand model, which uses a non-associated flow rule along with the concept of the state boundary surface possessing a critical and a compact state. It was observed that the granular trench might change the failure mechanism from deep plate to shallow plate as the failure surface can extend to the ground surface. The ultimate uplift capacity of anchor and the variation of surface deformation indicated a close agreement between the experiment and numerical model.

Description: Publication date: Available online 18 July 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Charalampos Saroglou, Vassilis Kallimogiannis The present paper investigates the effect of fracturing degree on P- and S-wave velocities in rock. The deformation of intact brittle rocks under loading conditions is characterized by a microcracking procedure, which occurs due to flaws in their microscopic structure and propagates through the intact rock, leading to shear fracture. This fracturing process is of fundamental significance as it affects the mechanical properties of the rock and hence the wave velocities. In order to determine the fracture mechanism and the effect of fracturing degree, samples were loaded at certain percentages of peak strength and ultrasonic wave velocity was recorded after every test. The fracturing degree was recorded on the outer surface of the sample and quantified by the use of the indices P 10 (traces of joints/m), P 20 (traces of joints/m 2 ) and P 21 (length of fractures/m 2 ). It was concluded that the wave velocity decreases exponentially with increasing fracturing degree. Additionally, the fracturing degree is described adequately with the proposed indices. Finally, other parameters concerning the fracture characteristics, rock type and scale influence were found to contribute to the velocity decay and need to be investigated further.

Description: Publication date: Available online 18 July 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Alireza Gholilou, Pouria Behnoud far, Stephanie Vialle, Mahyar Madadi Analysis of wellbore stability is such a key factor to have a successful drilling operation. Induced stresses are one of the main factors affecting wellbore instability and associated problems in drilling operations. These stresses are significantly impacted by pore pressure variation and thermal stresses in the fields. In order to eliminate wellbore instability problems, it is important to investigate the mechanisms of rock-fluid interaction with respect to thermal and mechanical aspects. In order to estimate the induced stresses, different mathematical models have been carried out. In this study, the field equations governing the problem have been derived based on the thermo-poroelastic theory and solved analytically in Laplace domain. The results are transferred to time domain using Fourier inverse method. Finite difference method is also utilized to validate the results. Pore pressure and temperature distribution around the wellbore have been focused and simulated here. Afterward, induced radial and tangential stresses for different cases of cooling and heating of formation are compared. In addition, the differences between thermo-poro-elastic and poro-elastic models in situation of permeable and impermeable wellbore are described. It is observed that cooling and pore pressure distribution reinforce the induced radial stress. Whereas, cooling can be a tool to control and reduce tangential stress induced due to invasion of drilling fluid. In the next step, safe mud window is obtained using Mohr-Coulomb, Mogi-Coulomb, and modified Lade failure criterion for different inclinations. Temperature and pore pressure distribution does not change the minimum allowable wellbore pressure significantly. However, upper limit of mud window is sensitive to induced stresses and it seems vital to consider changes in temperature and pressure to avoid any failures. The widest and narrowest mud windows are proposed by modified Lade and Mohr-Coulomb failure criterion, respectively.

Description: Publication date: Available online 23 March 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): G. Walton, M.S. Diederichs, L.R. Alejano, J. Arzúa

Description: Publication date: Available online 27 March 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Abdullah A. Al-Homidy, Mohammed H. Dahim, Ahmed K. Abd El Aal Improvement of properties of weak soils in terms of strength, durability and cost is the key from engineering point of view. The weak soils could be stabilized using mechanical and/or chemical methods. Agents added during chemical stabilization could improve the engineering properties of treated soils. Stabilizers utilized have to satisfy noticeable performance, durability, low price, and can be easily implemented. Since cement kiln dust (CKD) is industrial by-product, it would be a noble task if this waste material could be utilized for stabilization of sabkha soil. This study investigates the feasibility of utilizing CKD for improving the properties of sabkha soil. Soil samples are prepared with 2% cement and 10%, 20% or 30% CKD and are tested to determine their unconfined compressive strength (UCS), soaked California bearing ratio (CBR) and durability. Mechanism of stabilization is studied utilizing advanced techniques, such as the scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), backscattered electron image (BEI) and X-ray diffraction analysis (XRD). It is noted that the sabkha soil mixed with 2% cement and 30% CKD could be used as a sub-base material in rigid pavements. The incorporation of CKD leads to technical and economic benefits.

Description: Publication date: Available online 24 May 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Sadok Benmebarek, Insaf Saifi, Naima Benmebarek The undrained vertical bearing capacity of embedded foundation has been extensively studied using analytical and numerical methods. Through comparing the results of a circular embedded foundation in the literature, a significant difference between the bearing capacity factors and depth factors is observed. Based on the previous research findings, numerical computations using FLAC code are carried out in this study to evaluate the undrained bearing capacity of circular foundations with embedment ratios up to five for different base and side foundation roughness conditions. Unlike the foundation base, the roughness of the foundation side has a significant effect on the bearing capacity. The comparison of the present results with numerical studies available in the literature shows that the discrepancy is related to the procedures used to simulate the foundation side interface conditions and to the estimation of the bearing capacity.

Description: Publication date: Available online 6 November 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): S.M.Mahdi Niktabar, K.Seshagiri Rao, Amit Kumar Shrivastava Rock joints are often subjected to dynamic loads because of earthquake and blasting during mining and rock cutting. Hence, cyclic shear load can be induced along the joints and it is important to evaluate the shear behaviour of rock joint under this condition. In the present study synthetic rock joints were prepared with plaster of Paris. Regular joints were simulated by keeping regular asperity with asperity angles of 15 ˚ -15 ˚ and 30 ˚ -30 ˚ , and irregular rock joints which are closer to natural joints were replicated by keeping the asperity angles 15 ˚ -30 ˚ and 15 ˚ -45 ˚ . The sample size and amplitude of roughness were kept the same for both regular and irregular joints which were 298×298×125 mm and 5mm respectively. Shear test was performed on these joints on a large scale direct shear testing machine by keeping the frequency and amplitude of shear load under cyclic condition constant with different normal stress values. As expected, the shear strength of rock joints increased with the increase in the asperity angle and normal load during the first cycle of shearing or static load. With the increase of the number of shear cycles, the shear strength decreased for all the asperity angles but the rate of reduction was more in case of high asperity angles. Test results indicated that shear strength of irregular joints was higher than regular joints at different cycles of shearing at low normal stress. Shearing and degradation of joint asperities on regular joints were the same between loading and unloading, but for irregular joints were different. Shear strength and joint degradation were more significant on the slope of asperity with higher angles on the irregular joint until two angles of asperities became equal during the cycle of shearing and it started behaving like regular joints for subsequent cycles.

Description: Publication date: Available online 7 November 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Qixiang Fan, Xiating Feng, Wenlin Weng, Yilin Fan, Quan Jiang The columnar jointed rock mass (CJR), composed of polygonal cross-sectional columns cut by several groups of joints in various directions, was exposed during the excavations of the Baihetan hydropower station, China. In order to investigate the unloading performances and the stability conditions during excavation of the columns, an experimental field study was performed. Firstly, on-site investigations indicated that the geotechnical problems, including rock relaxation, cracking and collapse, were the most prominent for the CJR Class I that contains intensive joint network and the smallest column sizes. Comprehensive field tests, including deformation measurement by multi-point extensometers, ultrasonic wave testing, borehole television observation and stress monitoring of rock anchors, revealed that the time-dependent relaxation of the CJRs was marked. The practical excavation experiences for the Baihetan columnar jointed rock masses, such as blasting scheme, supporting time of shotcrete and rock bolts, were presented in the excavations of the diversion tunnels. These detailed investigations and practical construction experiences can provide helpful information for similar geotechnical works in jointed rock mass.

Description: Publication date: Available online 10 November 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Joar Tistel, Gustav Grimstad, Gudmund Eiksund The Norwegian Public Roads Administration (NPRA) is planning for an upgrade of the E39 highway route at the westcoast of Norway. Fixed links shall replace ferries at seven fjord crossings. Wide spans and large depths at the crossings combined with challenging subsea topography and environmental loads call for an extension of existing practice. A variety of bridge concepts are evaluated in the feasibility study. The structures will experience significant loads from dead weight, traffic and environment. Anchoring of these forces are thus one of the challenges met in the project. Large size subsea rock anchors are considered a viable alternative. These can be used for anchoring of floating structures but also with the purpose of increasing capacity of fixed structures. This paper presents first a thorough study of factors affecting rock anchor bond capacity. Laboratory testing of rock anchors subjected to cyclic loading is thereafter presented. Finally, the paper presents a model predicting the capacity of a rock anchor segment, in terms of a ribbed bar, subjected to a cyclic load history. The research assumes a failure mode occurring in the interface between the rock anchor and the surrounding grout. The constitutive behavior of the bonding interface is investigated for anchors subjected to cyclic one-way tension loads. The model utilizes the static bond capacity curve as a basis, defining the ultimate bond τ bu and the slip s 1 at τ bu . A limited number of input parameters are required to apply the model. The model defines the bond slip behavior and with that the belonging capacity depending on: the cyclic load level τ max cy /τ bu ), the cyclic load ratio (R = τ min cy /τ max cy ), and the number of load cycles (N). The constitutive model is intended to model short anchor lengths representing an incremental length of a complete rock anchor.

Description: Publication date: Available online 8 November 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Amir Hamidi, Saeed Tourchi, Fatemeh Kardooni In this paper, a critical state based thermo-elasto-plastic constitutive model is developed for destructured, naturally structured and artificially structured saturated clays. The model is an extension of the previously developed thermo-mechanical model by the authors for saturated clays, considering the effects of structure on the mechanical behaviors of the soil. It is based on change in the position of normal consolidation line (NCL) in a compression plane ( e − ln p ′ ) due to the soil’s structure and variation of temperature. The present model is able to simulate the mechanical behavior of structured saturated clays in a triaxial plane at elevated temperatures lower than the boiling point of water. An attempt has been made to use the lowest possible number of parameters compared with that of Cam-Clay model and to ensure that these new parameters have clear physical interpretations. The sufficiency of the model was verified by the test results on artificially and naturally structured soils using thermal triaxial tests.

Description: Publication date: Available online 21 September 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Robert Bertuzzi This paper presents two case studies where the rock mass modulus and in situ stress are estimated from the monitoring data obtained during the construction of underground excavations in Sydney, Australia. The case studies comprise the widening of existing twin road tunnels within Hawkesbury sandstone and the excavation of a large cavern within Ashfield shale. While back-analysis from detailed systematic monitoring has been previously published, this paper presents a relatively simple methodology to derive rock mass modulus and in situ stress from the relatively simple displacement data routinely recorded during tunnelling.

Description: Publication date: Available online 23 September 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Wei Yao, Taiming He, Kaiwen Xia Dynamic strength parameters are widely used in many rock engineering and mining engineering applications. However, there are no widely accepted dynamic failure models for rocks. In this work, the dynamic punch shear strength, uniaxial compressive strength (UCS) and tensile strength of fine-grained Fangshan marble are first systematically measured using a split Hopkinson pressure bar (SHPB) system. The pulse shaping technique is implemented to achieve dynamic force balance in SHPB tests. Experimental results show that the dynamic punch shear strength, dynamic UCS and dynamic tensile strength increase with the loading rate. A recently developed dynamic Mohr-Coulomb theory is then used to interpret the data. In this model, the internal friction angle ɸ is assumed to be loading rate independent and is obtained using the static strength values. The dynamic UCS and the dynamic tensile strength are predicted with the dynamic punch shear strength through the dynamic Mohr-Coulomb theory. Furthermore, the dynamic UCS is predicted with the dynamic tensile strength using the dynamic theory. The consistency between the predicted and measured dynamic strengths demonstrates that the dynamic Mohr-Coulomb theory is applicable to Fangshan marble.

Description: Publication date: Available online 12 January 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Ratan Das, P.K. Singh, Ashutosh Kainthola, S. Panthee, T.N. Singh Tunnelling related hazards are very common in the Himalayan terrain and a number of such instances have been reported. Several twin tunnels are being planned for transportation purposes which will require good understanding for prediction of tunnel deformation and surface settlement during the engineering life of the structure. The deformational behaviour, design of sequential excavation and support of any jointed rock mass are challenging during underground construction. We have raised several commonly assumed issues while performing stability analysis of underground opening at shallow depth. For this purpose, Kainchi-mod Nerchowck twin tunnels (Himachal Pradesh, India) are taken for in-depth analysis of the stability of two asymmetric tunnels to address the influence of topography, twin tunnel dimension and geometry. The host rock encountered during excavation is composed mainly of moderately to highly jointed grey sandstone, maroon sandstone and siltstones. In contrast to equidimensional tunnels where the maximum subsidence is observed vertically above the centreline of the tunnel, the result from the present study shows shifting of the maximum subsidence away from the tunnel centreline. The maximum subsidence of 0.99 mm is observed at 4.54 m left to the escape tunnel centreline whereas the maximum subsidence of 3.14 mm is observed at 8.89 m right to the main tunnel centreline. This shifting clearly indicates the influence of undulating topography and in-equidimensional noncircular tunnel.

Description: Publication date: Available online 19 January 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Ni An, Sahar Hemmati, Yu-jun Cui When modeling the soil/atmosphere interaction, it is of paramount importance to determine the net radiation flux. There are two common calculation methods for this purpose. Method 1 relies on use of air temperature, while Method 2 relies on use of both air and soil temperatures. Nowadays, there has been no consensus on the application of these two methods. In this study, the half-hourly data of solar radiation recorded at an experimental embankment were used to calculate the net radiation and long-wave radiation at different time-scales (half-hourly, hourly, and daily) using the two methods. The results show that, compared with Method 2 which has been widely adopted in agronomical, geotechnical and geo-environmental applications, Method 1 is more feasible for its simplicity and accuracy at shorter time-scale. Moreover, in case of longer time-scale, daily for instance, less variations of net radiation and long-wave radiation were obtained, suggesting that no detailed soil temperature variations can be obtained. In other words, shorter time-scales are preferred in determining net radiation flux.

Description: Publication date: Available online 20 January 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): L. Dormieux, E. Lemarchand, D. Kondo, S. Brach The present paper aims at giving some general ideas concerning the micromechanical approach of the strength of a porous material. It is shown that its determination theoretically amounts to solving a nonlinear boundary value problem defined on a representative elementary volume (REV). The principle of nonlinear homogenization is illustrated based on the case of a solid phase having a Green’s strength criterion. An original refinement of the so-called secant method (based on two reference strains) is also provided. The paper also describes the main feature of the Gurson’s model which implements the principle of limit analysis on a conceptual model of hollow sphere. The last part of the paper gives some ideas concerning poromechanical couplings.

Description: Publication date: Available online 5 January 2017 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Davinder Singh, Arvind Kumar The behavior of soluble salts contained in the municipal solid waste incinerator ash significantly affects the strength development and hardening reaction when it is introduced with cement. The present study emphasizes on the compaction and strength behavior of mix specimen of cement and MSWI ash. Series of tests such as unconfined compressive strength, split tensile strength and California bearing ratio and pH tests were carried out. Prior to this, the specimens were cured for 7, 14, and 28 days. The test results depicted that the maximum dry density decreases and optimum moisture content increases with the addition of cement. The test results also revealed that the cement inclusion increased the strength of the mix specimens. Thus, the combination of MSWI ash and cement can be used as light weight filling material in different structures like embankment and road construction.