ALBERT

Description: Publication date: Available online 29 December 2015 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Yankun Sun, Qi Li, Duoxing Yang, Xuehao Liu Carbon dioxide (CO 2 ) geosequestration in deep saline aquifers has been currently deemed as a preferable and practicable mitigation means for reducing anthropogenic greenhouse gases (GHGs) emissions to the atmosphere, as deep saline aquifers can offer the greatest potential from a capacity point of view. Hence, research on core-scale CO 2 /brine multiphase migration processes is of great significance for precisely estimating storage efficiency, ensuring storage security, and predicting the long-term effects of the sequestered CO 2 in subsurface saline aquifers. This review article initially presents a brief description of the essential aspects of CO 2 subsurface transport and geological trapping mechanisms, and then outlines the state-of-the-art laboratory core flooding experimental apparatus that has been adopted for simulating CO 2 injection and migration processes in the literature over the past decade. Finally, a summary of the characteristics, components and applications of publicly reported core flooding equipment as well as major research gaps and areas in need of further study are given in relevance to laboratory-scale core flooding experiments in CO 2 geosequestration under reservoir conditions.

Description: Publication date: Available online 29 December 2015 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Mojtaba Asadi Development of accurate and reliable models for predicting the strength of rocks and rock masses is one of the most common interests of geologists, civil and mining engineers and many others. Due to uncertainties in evaluation of effective parameters and also complicated nature of geological materials, it is difficult to estimate the strength precisely using theoretical approaches. On the other hand, intelligent approaches have attracted much attention as novel and effective tools of solving complicated problems in engineering practice over the past decades. In this paper, a new method is proposed for mining descriptive Mamdani fuzzy inference systems to predict the strength of intact rocks and anisotropic rock masses containing well-defined through-going joint. The proposed method initially employs a genetic algorithm (GA) to pick important rules from a preliminary rule base produced by grid partitioning and, subsequently, selected rules are given weights using the GA. Moreover, an information criterion is used during the first phase to optimize the models in terms of accuracy and complexity. The proposed hybrid method can be considered as a robust optimization task which produces promising results compared with previous approaches.

Description: Publication date: Available online 24 December 2015 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Matthew A. Perras, Mark S. Diederichs During the construction of an underground excavation, damage occurs in the surrounding rock mass due in large part to stress changes. While the predicted damage extent impacts profile selection and support design, the depth of damage is a critical aspect for the design of permeability sensitive excavations, such as a deep geological repository (DGR) for nuclear waste. Review of literature regarding the depth of excavation damage zones (EDZs) indicates three zones are common and typically related to stress induced damage. Based on past developments related to brittle damage prediction using continuum modelling, the depth of the EDZs has been examined numerically. One method to capture stress induced damage in conventional engineering software is the damage initiation and spalling limit (DISL) approach. The variability of depths predicted using the DISL approach has been evaluated and guidelines are suggested for determining the depth of the EDZs around circular excavations in brittle rock masses. Of the inputs evaluated, it was found that the tensile strength produces the greatest variation in the depth of the EDZs. The results were evaluated statistically to determine the best fit relation between the model inputs and the depth of the EDZs. The best correlation and least variation were found for the outer EDZ and the highly damaged zone (HDZ) showed the greatest variation. Predictive equations for different EDZs have been suggested and the maximum numerical EDZ depths, represented by the 68% prediction interval, agreed well with the empirical evidence. This suggests that the numerical limits can be used for preliminary depth prediction of the EDZs in brittle rock for circular excavations.

Description: Publication date: Available online 21 December 2015 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): J. Connor Langford, N. Vlachopoulos, M.S. Diederichs With the scale and cost of geotechnical engineering projects increasing rapidly over the past few decades, there is a clear need for the careful consideration of calculated risks in design. While risk is typically dealt with subjectively through the use of conservative design parameters, with the advent of reliability-based methods, this no longer needs to be the case. Instead, a quantitative risk approach can be considered that incorporates uncertainty in ground conditions directly into the design process to determine the variable ground response and support loads. This allows for the optimization of support on the basis of both worker safety and economic risk. This paper presents the application of such an approach to review the design of the initial lining system along a section of the Driskos twin tunnels as part of the Egnatia Odos highway in northern Greece. Along this section of tunnel, weak rock masses were encountered as well as high in situ stress conditions, which led to excessive deformations and failure of the as built temporary support. Monitoring data were used to validate the rock mass parameters selected in this area and a risk approach was used to determine, in hindsight, the most appropriate support category with respect to the cost of installation and expected cost of failure. Different construction sequences were also considered in the context of both convenience and risk cost.

Description: Publication date: Available online 17 December 2015 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Mohammad Hamed Fasihnikoutalab, Afshin Asadi, Bujang Kim Huat, Paul Westgate, Richard J. Ball, Shahram Pourakbar Olivine sand is a natural mineral, which, when added to soil, can improve the soil’s mechanical properties while also sequester carbon dioxide (CO 2 ) from the surrounding environment. The originality of this paper stems from the novel two-stage approach. In the first stage, natural carbonation of olivine and carbonation of olivine treated soil under different CO 2 pressures and times were investigated. In this stage, the unconfined compression test was used as a tool to evaluate the strength performance. In the second stage, details of the installation and performance of carbonated olivine columns using a laboratory-scale model were investigated. In this respect, olivine was mixed with the natural soil using the auger and the columns were then carbonated with gaseous CO 2 . The unconfined compressive strengths of soil in the first stage increased by up to 120% compared to those of the natural untreated soil. The strength development was found to be proportional to the CO 2 pressure and carbonation period. Microstructural analyses indicated the presence of magnesite on the surface of carbonated olivine-treated soil, demonstrating that modified physical properties provided a stronger and stiffer matrix. The performance of the carbonated olivine-soil columns, in terms of ultimate bearing capacity, showed that the carbonation procedure occurred rapidly and yielded a bearing capacity value of 120 kPa. Results of this study are of significance to the construction industry as the feasibility of carbonated olivine for strengthening and stabilizing soil is validated. Its applicability lies in a range of different geotechnical applications whilst also mitigates the global warming through the sequestration of CO 2 .

Description: Publication date: Available online 17 December 2015 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Felipe Carvalho Bungenstab, Kátia Vanessa Bicalho The design of footings on sands is often controlled by settlement rather than bearing capacity. Therefore, settlement predictions are essential in the design of shallow foundations. However, predicted settlements of footings are highly dependent on the chosen elastic modulus and the used method. This paper presents the use of probabilistic analysis to evaluate the variability of predicted settlements of footings on sands, focusing on the load curve (predicted settlements) characterization. Three methodologies, the first- and second-order second-moment (FOSM and SOSM), and Monte Carlo simulation (MCS), for calculating the mean and variance of the estimated settlements through Schmertmann (1970)’s equation, are presented and discussed. The soil beneath the footing is treated as an uncorrelated layered material, so the total settlement and variance are found by adding up the increments of the layers. The deformability modulus ( E S i ) is considered as the only independent random variable. As an example of application, a hypothetical case of a typical subsoil in the state of Espirito Santo, southeast of Brazil, is evaluated. The results indicate that there is a significant similarity between the SOSM and MCS methods, while the FOSM method underestimates the results due to the non-consideration of the high-order terms in Taylor’s series. The contribution of the knowledge of the uncertainties in settlement prediction can provide a safer design.

Description: Publication date: Available online 17 December 2015 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Meifeng Cai Rockburst is a kind of artificial earthquake induced by human activities, such as mining excavations. The mechanism of rockburst induced by mining disturbance is revealed in terms of energy in this context. For understanding the rockburst mechanism, two necessary conditions for the occurrence of rockburst are presented: (1) the rock mass has the capability to store huge amount of energy and possesses a strong bumping-prone characteristic when damaged; and (2) the geological conditions in the mining area have favorable geo-stress environments that can form high-stress concentration area and accumulate huge energy. These two conditions are also the basic criteria for prediction of rockburst. In view of energy analysis, it is observed that artificial and natural earthquakes have similar regularities in many aspects, such as the relationship between the energy value and burst magnitude. By using the relationship between energy and magnitude of natural earthquake, rockburst is predicted by disturbance energy analysis. A practical example is illustrated using the above-mentioned theorem and technique to predict rockburst in a gold mine in China. Finally, the prevention and control techniques of rockburst are also provided based on the knowledge of the rockburst mechanism.

Description: Publication date: Available online 11 December 2015 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): P.K. Singh, M.P. Roy, R.K. Paswan, Md. Sarim, Suraj Kumar, Rakesh Ranjan Jha The blasting operation plays a pivotal role in the overall economics of opencast mines. The blasting sub-system affects all the other associated sub-systems, i.e. loading, transport, crushing and milling operations. Fragmentation control through effective blast design and its effect on productivity are the challenging tasks for practicing blasting engineer due to inadequate knowledge of actual explosive energy released in the borehole, varying initiation practice in blast design and its effect on explosive energy release characteristic. This paper describes the result of a systematic study on the impact of blast design parameters on rock fragmentation at three mines in India. The mines use draglines and shovel-dumper combination for removal of overburden. Despite its pivotal role in controlling the overall economics of a mining operation, the expected blasting performance is often judged almost exclusively on the basis of poorly defined parameters such as powder factor and is often qualitative which results in very subjective assessment of blasting performance. Such an approach is very poor substitutes for accurate assessment of explosive and blasting performance. Ninety one blasts were conducted with varying blast designs and charging patterns, and their impacts on the rock fragmentation were documented. A high-speed camera was deployed to record the detonation sequences of the blasts. The efficiency of the loading machines was also correlated with the mean fragment size obtained from the fragmentation analyses.

Description: Publication date: December 2015 Source: Journal of Rock Mechanics and Geotechnical Engineering, Volume 7, Issue 6

Description: Publication date: Available online 8 December 2015 Source: Journal of Rock Mechanics and Geotechnical Engineering Author(s): Ferri Hassani, Pejman M. Nekoovaght, Nima Gharib Demand is growing for explosive-free rock breakage systems for civil and mining engineering, and space industry applications. This paper highlights the work being undertaken in the Geomechanics Laboratory of McGill University to make a real application of microwave-assisted mechanical rock breakage to full-face tunneling machines and drilling. Comprehensive laboratory tests investigated the effect of microwave radiation on temperature profiles and strength reduction in hard rocks (norite, granite, and basalt) for a range of exposure times and microwave power levels. The heating rate on the surface of the rock specimens linearly decreased with distance between the sample and the microwave antenna, regardless of microwave power level and exposure time. Tensile and uniaxial compressive strengths were reduced with increasing exposure time and power level. Scanning electron micrographs (SEMs) highlighted fracture development in treated basalt. It was concluded that the microwave power level has a strong positive influence on the amount of heat damage induced to the rock surface. Numerical simulations of electric field intensity and wave propagation conducted with COMSOL Multiphysics® software generated temperature profiles that were in close agreement with experimental results.