Rock Mechanics Bulletin最新文献

A simplified two-stage method was employed to provide an explicit solution for the time-dependent tunnel-rock interaction, considering the generalized Zhang-Zhu strength criterion. Additionally, a simplified mechanical model of the yielding support structure was established. The tunnel excavation is simplified to a two-stage process: the first stage is affected by the longitudinal effect, while the second stage is affected by rheological behavior. Two cases are considered: one is that the rigid support is constructed during the first stage, and the other is that constructed at the second stage. Distinguished by the support timing at the seconde stage, different kinds of the “yield-resist combination” support method are divided into three categories: “yield before resist” support, “yield-resist” support, and “control-yield-resist” support. Results show that the support reaction of “control-yield-resist” is much higher than that of “yield before resist” if the initial geostress is not very high, but the effect is not obvious on controlling the surrounding rock deformation. So, the “yield before resist” support is much more economical and practical when the ground stress is not very high. However, under high geostress condition, through applying relatively high support reaction actively to surrounding rock at the first stage, the “control-yield-resist” support is superior in controlling the deformation rate of surrounding rock. Therefore, in the high geostress environment, it is recommended to construct prestressed yielding anchor immediately after excavation, and then construct rigid support after the surrounding rock deformation reaches the predetermined deformation.

Bimrocks are characterized by their geotechnically significant blocky structure, presenting complex shear behavior. This study investigates the shear behavior and dilatancy of bimrocks featuring a rock-like matrix, such as conglomerates. The study addresses a gap in current research, which has predominantly examined the shear behavior of soil-matrix bimrocks (bimsoils). Laboratory direct shear tests were performed on idealized models with varying volumetric block proportions (VBPs). The results highlight that blocks exert both positive and negative effects on shear strength, dilation, and block breakage factor (BF), depending on VBP. Results indicate 40% and 60% as critical VBPs, revealing distinct shear strength trends within this range, contrary to the dominant downward trend. Blocks positively impact dilation and BF between 20% and 50% VBP, while negatively affecting them beyond this range. Blocky skeleton inherently promotes stable dilatancy under normal stress increments and intensifies stress dependency of shear strength. Variations in dilation angle concerning normal stress and VBP suggest the potential for characterizing this factor using equivalent strength and roughness, akin to rockfill materials. Indirect assessments of equivalent strength revealed positive effects of blocks when VBP was between 30% and 70%. Lastly, the findings indicate that blocks notably impact pre- and post-peak behaviors by reducing shear stiffness and inducing local hardening phases. This study also discusses the similarities and distinctions in the function of blocks within soil-like and rock-like matrices. It offers new insights into the exact role of blocks in bimrock shear behavior beyond the traditional interpretation through the variation of friction and cohesion.

Cyclic shear tests on rock joints serve as a practical strategy for understanding the shear behavior of jointed rock masses under seismic conditions. We explored the cyclic shear behavior of en-echelon and how joint persistence and test conditions (initial normal stress, normal stiffness, shear velocity, and cyclic distance) influence it through cyclic shear tests under CNS conditions. The results revealed a through-going shear zone induced by cyclic loads, characterized by abrasive rupture surfaces and brecciated material. Key findings included that increased joint persistence enlarged and smoothened the shear zone, while increased initial normal stress and cyclic distance, and decreased normal stiffness and shear velocity, diminished and roughened the brecciated material. Shear strength decreased across shear cycles, with the most significant reduction in the initial shear cycle. After ten cycles, the shear strength damage factor D varied from 0.785 to 0.909. Shear strength degradation was particularly sensitive to normal stiffness and cyclic distance. Low joint persistence, high initial normal stress, high normal stiffness, slow shear velocity, and large cyclic distance were the most destabilizing combinations. Cyclic loads significantly compressed en-echelon joints, with compressibility highly dependent on normal stress and stiffness. The frictional coefficient initially declined and then increased under a rising cycle number. This work provides crucial insights for understanding and predicting the mechanical response of en-echelon joints under seismic conditions.

In this study, laboratory testing and numerical simulation methods are used to investigate the mechanical behavior and perform fracture prediction of a novel high-strength and high-toughness steel with a negative Poisson's ratio (NPR) effect under combined tensile-shear loading conditions. A test device capable of meeting different tensile-shear combination test angles is designed and manufactured, wherein the mechanical experiments on the NPR (Negative Poisson's Ratio) steel specimens are carried out at various testing angles. Q235 steel and MG400 steel are used as experimental control groups. The results show that the mechanical deformation of NPR steel is significantly better than that of Q235 steel and MG400 steel. Its tensile-shear test curve has no yield plateau and it has quasi-ideal elastic-plastic mechanical properties. The loading direction gradually changes from tension-dominated to shear-dominated as the tension-shear angle increases, and the strength and deformation of the specimens show a decreasing trend. Based on the laboratory test results, a finite element numerical model of NPR steel is established. A series of numerical simulations are carried out under the conditions of different tension and shear angles and the average stress triaxiality and fracture strain data are obtained. The fracture data of NPR steel are fitted using the Johnson-Cook fracture criterion, and the Johnson-Cook fracture parameters under the tensile-shear test conditions of NPR steel are thus obtained. The numerical simulation verifies that the fracture model can accurately predict the tensile-shear fracture behavior of NPR steel.

With the growing prominence of recycling projects of groundwater, the attention towards subsidence concerns in geological formations is intensifying. However, due to the long evolutionary time and complex underground discontinuities, the deformation field and subsidence mechanism are difficult to obtain. To this concern, this study implemented the Hydro-Mechanical Coupled Discontinuous Deformation Analysis (HM-DDA) in a groundwater recycling project located at a goaf mining site. The method for establishing numerical stratigraphic models and determining the required numerical parameters is introduced. This contributes to the comprehensive reconstruction of changes in in-situ stress within the goaf area, encompassing the initial stress equilibrium state, as well as the processes of water pumping and injection. The results indicated that the water injection process mitigated stress concentrations at both ends of the goaf area. Specifically, a 30-m rise in water head resulted in a corresponding elevation of the ground surface by 3.94 ​cm.

Landslides are one of the geological disasters with wide distribution, high impact and serious damage around the world. Landslide risk assessment can help us know the risk of landslides occurring, which is an effective way to prevent landslide disasters in advance. In recent decades, artificial intelligence (AI) has developed rapidly and has been used in a wide range of applications, especially for natural hazards. Based on the published literatures, this paper presents a detailed review of AI applications in landslide risk assessment. Three key areas where the application of AI is prominent are identified, including landslide detection, landslide susceptibility assessment, and prediction of landslide displacement. Machine learning (ML) containing deep learning (DL) has emerged as the primary technology which has been considered successfully due to its ability to quantify complex nonlinear relationships of soil structures and landslide predisposing factors. Among the algorithms, convolutional neural networks (CNNs) and recurrent neural networks (RNNs) are two models that are most widely used with satisfactory results in landslide risk assessment. The generalization ability, sampling training strategies, and hyper-parameters optimization of these models are crucial and should be carefully considered. The challenges and opportunities of AI applications are also fully discussed to provide suggestions for future research in landslide risk assessment.

During the construction and operation of a pumped storage power station in an abandoned mine, the soft rock-coal body structure, comprising the roof and the residual coal pillars, encounters a complex stress environment characterized by cyclic loads. The study of its failure mechanism under cyclic dynamic loading holds significant theoretical and practical importance to stay the safety and stability of the abandoned mine pumped storage power station. In this paper, we take “roof-residual coal pillar” soft rock-coal combinations with different percentages of rock as the research object, and study their mechanical properties, failure mechanism, energy evolution characteristics and acoustic emission distribution characteristics through cyclic dynamic loading experiments. The results of the experiment indicate that: (1) Both weak cyclic dynamic loading and high rock percentage enhance the deformation resistance of soft rock-coal combinations. Under low-disturbance horizontal cyclic loading, its peak strength and modulus of elasticity increase with increasing rock percentage. (2) Under low-disturbance horizontal cyclic loading, an increasing trend is observed in the average total strain energy density, dissipation energy density, and elastic energy density of the combinations as the percentage of rock increases. (3) Under low-disturbance horizontal cyclic loading, as the percentage of rock increases in the soft rock-coal combinations, the degree of failure in the rock body part progressively intensifies, while the destruction of the coal portion progressively decreases. (4) The large number of acoustic emission signals are generated at the instant of destabilization and destruction of the coal-rock combinations, mainly dominated by the signals generated by the destruction of the coal body. Acoustic emission counts and absolute energy at key point N₂ decrease as the percentage of rock increases. The b value is primarily distributed in the cyclic dynamic loading stage and the failure stage, both displaying zones of sudden increase and sudden decrease in b value.

Bench blasting is commonly used in open-pit mining. Some design parameters such as positions of hole packing and caving holes have great influences on the blasting effects. In this work, with a hybrid discrete-finite element method, numerical simulations of bench blasting are conducted, capturing the whole continuous-discontinuous processes. Considering two engineering cases, the influences of hole packing and caving holes are evaluated. The numerical results not only lead to some improved designs by relocating the packing positions and caving holes but also indicate the reliability of the adopted numerical tools.

Blasting test research was conducted on iron ore specimens with variable line density charging structures. Computer tomography (CT), digital image processing, and three-dimensional model reconstruction techniques were used to analyze the damage characteristics of iron ore specimens after blasting based on the calculated number of box dimensions. The results show that increasing the variable line density section charge uncoupling coefficient reduces the overall damage to the specimen by up to 1.73%, indicating that the overall damage size negatively correlates with the size of the variable line density section charge uncoupling coefficient. The damage characteristics of iron ore specimens from different layers (uncoupled charging section, transition section, coupled charging section) have some variability; when the uncoupling coefficient of the uncoupled charging section was reduced, the uncoupled section of the center of the damaged layer increased and then reduced. In contrast, the transition section shows a trend of increase, and the coupled section shows a minor difference, fully demonstrating the change in the variable line density section of the uncoupling coefficient of the specimen blasting damage effects. This study concludes that in the actual blasting project, choosing a reasonable variable line charge density structure can make the release of explosive blast energy more uniform to efficiently and thoroughly use explosive power to improve the iron ore crushing effect.

For solving the computationally intensive problem encountered by the discrete element method (DEM) in simulating large-scale engineering problems, it is essential to establish a numerical model that can effectively simulate large-scale rocks. In this study, the coarse-graining effect of a linear-Mindlin with bonding model was studied in the unconfined compression strength (UCS) and Brazilian tensile strength (BTS) tests. We found that the main reason for the coarse-graining effect of the BTS tests is that the type I fracture toughness is positively correlated with the size of the particles. Based on the results analysis and fracture mechanics, the coarse-grained (CG) modeling theory was combined with a bonded particle model (BPM) for the first time and a coarse-grained bonded particle model (CG-BPM) was developed, which can be effectively used to model the tensile strength of large-scale rocks with different particle sizes. The excavation damage zone (EDZ) in an underground research laboratory (URL) was selected as an application case, which shows that the coarse-grained bonding model presented in this paper is more accurate and reliable than the traditional one in large-scale rock simulation, at least in the scenario where tensile failure is dominant.