Rock Mechanics Bulletin最新文献

A macroscopic yield criterion has been derived in the present work for a double saturated porous medium with a spheroidal pore at the mesocale and spherical pores at the microscale. These two types of pores are well separated at two different scales. The meso spheroidal pore saturated by a pore pressure which is different from the one in the micro spherical pores. A Drucker-Prager type criterion is adopted for the solid phase at the microscopic scale to describe its asymmetric behavior between tension and compression. The methodology to formulate this criterion is based on the limit analysis approach of a spheroidal volume containing a confocal spheroidal pore subjected to a uniform strain rate boundary conditions. The matrix at the mesoscopic scale obeys to a general elliptic yield criterion. Based on a two-step homogenization step, the influence of meso-pore shape (spherical, prolate or oblate), micro-porosity, meso-porosity and the effect of pore pressures at different scales are taken into account explicitly by this macroscopic yield criterion.

This paper describes a numerical algorithm for solving the classic problem of a plane strain (KGD) fracture propagating in an impermeable elastic medium with zero toughness. The method, which takes advantage of the self-similar nature of the solution, combines a domain-based scheme to solve the elasticity equations and a finite volume method to solve the nonlinear lubrication equation. This work represents a first step towards developing a model able to account for pore pressure diffusion in the medium and corresponding poroelastic effects, noting that these processes are more efficiently solved using a domain-based rather than a boundary integral method. To enhance the efficiency and accuracy of the numerical scheme, the far-field crack asymptotics is embedded in the discretized elastic relationship between the fluid pressure and the crack opening, while the coupled fluid-solid tip asymptote is enforced in a weak form when solving the nonlinear lubrication equation. The proposed technique yields results that closely match the analytical solution, even with a coarse mesh. This approach offers potential for addressing more complex hydraulic fracturing problems in the future.

This study aims to clarity the failure mechanism of sidewall rockburst of highly stressed D-shape tunnel triggered by impact load. Using the biaxial Hopkinson pressure bar (BHPB) system, we have developed experimental capabilities to study the sidewall rockburst of D-shape tunnel by applying various prestresses, including horizontal and vertical static stresses, to sand prefabricated D-shape hole specimen, followed by impact loads. High-speed (HS) camera and digital image correlation (DIC) were used to tracked the process and strain field of the sidewall rockburst. The test results reveal that the process of sidewall rockburst can be summarized as: calm stage, crack initiation, propagation, and coalesce stage, spalling stage and rock fragments ejection stage. During the rockburst process, the surrounding rock experienced spalling and violent ejection, involving both tensile and tensile-shear failure. The mechanism of sidewall rockburst under the coupled of static stress and impact loads has been elucidated, i.e., the static prestress determines the initial stress and strain distribution, and the horizontal prestress influences the affected range and strain values of strain concentration zone; the impact load disrupts the original static stress equilibrium, inducing alterations in the stress and strain of the surrounding rock and triggering sidewall rockburst.

In many engineering applications, it is essential to have information about rocks that inherently contain pre-existing flaws under dynamic loading conditions. Dynamic impact tests are conducted on samples with varying flaw angles using the split Hopkinson pressure bar (SHPB) test system and the Digital Image Correlation system (DIC). The characteristics of the samples after dynamic loading, including dynamic strength, energy dissipation, and fractal fracture, are compared and analyzed. As the flaw angle increases, the peak stress and strain exhibit a typical V-shaped pattern, reaching the minimum value at 30°, and the initial initiation position shifts from the flaw tips to the middle of the flaw. Failure modes can be divided into three modes depending on the flaw angle. The progressive failure process, taking into account the heterogeneity of the rock, is demonstrated by developing an elastic damage constitutive model that uses dynamic compression and tensile tests to parameterize it. As the flaw angle increases, the initial damage zone also moves from the flaw tips to the middle of the flaw. Failures around the hole with redistributed stress are observed, and the failure mechanisms can be explained with the aid of strain energy density (SED). Using fracture mechanics, the analytical solution of stress around the flaw is provided, and the variation of crack initiation angle, stress distribution, and energy dissipation under different flaw angles is theoretically explained, which is in good agreement with the experimental and simulated results.

In many construction projects, a proactive slope stability evaluation is a prerequisite. Although many deterministic or non-deterministic approaches have been commonly used, metaheuristic approaches have resulted in high precision and significant outcomes for slope stability analysis problems. The current work focuses on the reliable assessment of critical failure surfaces associated with the least factor of safety value in both homogeneous and non-homogeneous slopes using a new simplified meta-heuristic approach called optics-inspired optimization (OIO). The algorithm utilizes six different LEM methods as a fitness function for deriving the factor of safety. Experimental analysis over three benchmark studies has been performed to demonstrate the algorithm's robustness and effectiveness. The implementation found more robust results as compared to previous studies. Meanwhile, the algorithm's statistical implication is conducted using the ANOVA test, which inferred better outcomes. With this interpretation, the approach claims to be suitable and efficient for slope stability analysis.

Fracture propagation under mixed-mode loading conditions prevails in many natural geological processes and deep engineering projects, while the corresponding numerical simulation is very challenging in rock mechanics, especially in 3D cases. In most previous studies, the complexity of 3D fracture geometry was over-simplified, and model III loading was often not considered. In this study, we propose to use an efficient stress-based Schöllmann criterion combined with Displacement Discontinuity Method (DDM) to model 3D fracture propagation under arbitrary I ​+ ​II ​+ ​III mixed-mode loading conditions. A novel curve-smoothing algorithm is developed to smoothen the fracture front during propagation, which significantly enhances the model's ability in dealing with complex 3D fracture geometry. In particular, we adopt two different solution schemes, namely staggered and monolithic, to simulate mode I fracture propagation in the case of hydraulic fracturing. The accuracy, efficiency and convergency of the two solution schemes are compared in detail. Our research findings suggest that the degree of coupling between fracture aperture and fluid pressure in hydraulic fracturing lies somewhere between one-way and two-way, which favors the staggered solution scheme. To further test our new model, we provide three additional numerical examples associated with 3D fracture propagation under various mixed-mode loading conditions. Our model shows excellent performance in efficiently locating the new fracture front and reliably capturing the complex 3D fracture geometry. This study provides a generic algorithm to model high-fidelity 3D fracture propagation without simplifying fracture geometry or loading conditions, making it widely applicable to fracture-propagation-related problems.

The evaluation of rock damage behaviour is an important requirement for ensuring stability control and safety prediction in rock engineering. However, they have not been able to obtain sufficiently accurate and dynamic results due to the insufficient evaluation method. In this study, by means of fractals and unit series division, a unit series-parallel conductive model of damaged rock is derived, and a new evaluation method of rock damage under uniaxial compression was proposed. Rock was damaged by uniaxial compression, while electrical measurements and X-ray microscopy tests were performed to obtain the damaged rock resistivity, porosity, and fractal dimension variation. By establishing the relationship between defined meso-damage factor and resistivity, rock damage evolution law under axial compression was obtained. The results indicate that the growth trend was agree with the classical statistical damage model, which verified the accuracy of the results obtained by the proposed method. Moreover, as the strain increased, the damage factor determined by resistivity gradually decreased to −0.06 firstly and then increased rapidly to 0.79. Different from previous damage evolution law, brittle failure was observed and the cracks development in each stage was considered, including the closure (negative damage) and expansion (positive damage) of cracks.

With global greenhouse gas emissions hitting record highs in 2021, CO₂ geological sequestration (CGS) is the most realistic and feasible technology to ensure large-scale carbon reduction to achieve global carbon capping and carbon neutrality goals. Both coalbed methane and shale gas have the characteristics of self-generation and self-storage, which is considered to be a valuable target reservoir for geological sequestration of CO₂. After a high volume of CO₂ is injected into unconventional coal seams and shale gas reservoirs, many geomechanical issues may be induced, resulting in leakage. Therefore, it is crucial to evaluate the geomechanical risks of CO₂ geological sequestration. In this article, global CO₂ emissions and geological resources available for sequestration are teased out. The effects of coupled CO₂-water-rock-driven geomechanical, geophysical, and geochemical interactions on the evolution of rock physical properties and pore characteristics, as well as caprock sealing, are discussed. The caprock failure and its inducing mechanism are analyzed, and the criteria for predicting the occurrence of risk are summarized, which is necessary for pressure management and risk prevention. To serve as a benchmark for CO₂ sequestration in unconventional coal seams and shale gas reservoirs.

Experimental rock mechanics testing provides a controlled and effective method for measuring physical properties, their dependencies, and their evolution due to the addition of localized microcracks. To understand the contributions of microcracks to first order changes in compliance, the behavior of initial undamaged properties of a material should be comprehensively investigated as a function of stress, load path, and load history. We perform a comprehensive study of elastic properties and their dependence on a variety of materials exhibiting nonlinearity, and varying levels of anisotropy in elastic stiffnesses. We programmatically perturb the testing environment of the specimens under triaxial stresses. Elastic moduli are measured within each test, and along multiple discrete loading paths for multistage tests as a function of stress, focusing on a set launch point. Four single stage triaxial tests per rock type are performed to calculate Mohr-Coulomb failure criteria, and ultrasonic velocities are captured during compression for establishing the upper bound of elastic behavior. Shear wave velocity for granite experiences a maximum value at a lower differential stress than maximum volumetric strain. Sandstone displays a similar trend at the highest confining pressure, while these two maxima converge under the lowest confining pressure.

To explain the effect of joint roughness on joint peak shear strength (JPSS) and investigate the effect of different contact states of joint surface on JPSS, we try to clarify the physical mechanism of the effect of joint cavity percentage (JCP) on JPSS from the perspective of the three-dimensional (3D) distribution characteristics of the actual contact joint surface, and propose a JPSS model considering the JCP. Shear tests for red sandstone joints with three different surface morphologies and three different JCPs were performed under constant normal load condition. Based on test fitting results, the reduction effect of the JCP on JPSS is investigated, and a JPSS model for cavity-containing joints is obtained. However, the above model only considers the influence of JCP by fitting test data, and does not reveal the physical mechanism of JCP affecting the JPSS. Based on the peak dilation angle model for consideration of the actual contact joint morphology, and the influence of JCP on the roughness of the actual contact joint surface, a theoretical model of the JPSS considering the JCP is proposed. The derivation process does not depend on the test fitting, but is entirely based on the joint mechanical law, and its physical significance is clear. It is proposed that the essence of the influence of the JCP on JPSS is that the JCP first affects the normal stress of the actual contact joints, further affects the roughness of actual contact joints, and then affects the shear strength.