Traditional active earth pressure evaluations considering seepage are typically deterministic, assuming uniform soil layers. However, soil hydraulic properties exhibit the obvious spatial variability due to geomorphological processes or poor construction control. To address this, the random limit analysis method (RLAM) is employed to investigate the influence of spatial variability of saturated hydraulic conductivity on active earth pressure. To combine random field simulations with the limit analysis-based evaluation method, this study discretizes the conventional three-dimensional (3D) rotational failure mechanism. Owing to the energy dissipation principle, the explicit expression of 3D active earth pressures can be derived. The proposed method's validity is demonstrated through comparisons with available analytical solutions, deterministic numerical calculations, and random finite difference method (RFDM). RLAM integrating with Monte Carlo simulations (MCS) in MATLAB, facilitates the probabilistic analysis of the active earth pressure to be evaluated. The findings indicate that the present method not only incorporates the spatial variability of hydraulic properties, but also enhances the computational efficiency of calculating active earth pressures compared to the RFDM. Based on extensive uncertainty analyses, this study proposes a system reliability evaluation method for semi-gravity retaining walls, accounting for the spatial variability of saturated hydraulic conductivity. The results reveal that under different random field design scenarios, all decay curves of system failure probabilities for a semi-gravity retaining wall intersect within a specific range, referred to herein as the "turning region". Furthermore, as the normalized horizontal autocorrelation distance, anisotropic ratio and coefficient of variation increase, the effective influence zone of the wall design index on system failure probability gradually expands, offering valuable guidance for the design and construction of semi-gravity retaining walls.

The soil-water retention and soil shrinkage characteristics are both crucial constitutive relations for unsaturated soils. Although existing research has explored the correlation between these two characteristics to some extent, the underlying mechanisms remain inadequately investigated. To investigate the correlation between the soil-water retention and soil shrinkage behavior, a series of soil-water retention and soil shrinkage tests is performed on compacted clays over a wide suction range (0-367 MPa). The test results show that the pore water in compacted clays is first expelled from large pores in low suction range. The drainage of pore water at low suctions is predominantly responsible for the phase of structural shrinkage in the soil shrinkage curve. The consistency between the characteristic transitional water contents in the soil shrinkage curve (SSC) and the inflection points in the soil-water retention curve (SWRC) is identified for all the compacted clays. The bimodal pore-size distributions (PSDs) of different clayey soils are obtained using the mercury intrusion porosimetry. The bimodal pore-size distribution characterization is the intrinsic factor in shaping the bimodal morphology in the SWRC over a wide suction range. The low proportion of micropores in clays is responsible to the indistinct zero-shrinkage stage of the SSC. The microstructure measured by the scanning electron microscope indicates the manifestation of aggregation effects during desaturation process. The results demonstrate that soil shrinkage is primarily caused by the contraction of inter-aggregate pores, rather than the evolution of intra-aggregate pores. The findings can greatly enhance the understanding of the soil-water retention and mechanical behavior of compacted clays in varying water content conditions.

Callovo-Oxfordian (COx) claystone has been selected as the host rock formation for the deep geological disposal of radioactive waste in France, called the Cigéo project. The excavation of drifts in the COx formation induced damage zones with an anisotropic shape, while the stress state around the drifts is almost isotropic. This is due to the anisotropic properties of the host rock formation and the instability caused by the brittle damage. In this study, the mechanical anisotropy of COx claystone was investigated through a triaxial shear test, where the axial stress was maintained while the lateral stress was decreased. Such a method was proposed for simulating one of the possible unloading paths involved during the excavation. The triaxial samples were prepared along different directions based on the angle between the axial loading direction and the one perpendicular to the bedding plane. Results show that the stress-strain curve exhibited an elasto-plastic pattern. With increasing deviatoric stress, a minor decline in Young's modulus E was observed, suggesting progressive damage behaviour. The shear strength changed with increasing the loading angle, showing the anisotropic property of COx claystone. Moreover, the results in this study and collected from other works show a time-dependent behaviour of COx claystone. It is attributed to the coupled effect of creep and pore pressure dissipation inside claystone.

This study investigates particle crushing mechanisms in granular soils during shearing through staged triaxial compression experiments performed at prescribed axial strains and varying confining stresses, integrating a high-performance acoustic emission (AE) measurement system. The study analyzed particle crushing-related parameters using grain size distribution (GSD)-based indices (relative breakage index B_r and its rate ΔB_r) and AE-based parameters (high-frequency AE hits and hit rates ). The results confirm the feasibility of high-frequency AEs (>100 kHz) in comprehensive quantification of particle crushing, with a strong linear relationship observed between and B_r. Significant particle crushing occurs within the initial 5 % of axial strain, which correlates with the yielding and peak-stress phases. This process yields fragments with a size range of 0.425-2 mm. Increased confining stresses result in a steady rise in B_r and , suggesting that large strains are required for stable particle grading. The evolution trends of different high-frequency AE ranges reveal a shift to complex crushing mechanisms, such as particle abrasion/grinding and corner breakage/particle splitting, highlighting the role of stress and strain levels in influencing particle damage behavior.

Investigating the mechanical behavior and microstructural evolution of granite under high temperatures is crucial for optimizing fracturing strategies and ensuring reservoir sustainability in enhanced geothermal systems (EGS) at the Qiabuqia geothermal field, China. This study conducted triaxial compression tests on granite from the Qinghai Gonghe Basin under temperature from 25 ℃ to 300 ℃, examining the effects of temperature and confining pressure on the mechanical properties and energy evolution of the granite. Additionally, X-ray diffraction (XRD) analysis and nanoindentation tests were employed to assess changes in micro-mechanical properties and mineral compositions. Furthermore, fracture mechanics principles, incorporating thermal stress effects, were utilized to calculate the initiation pressure of reservoirs at an engineering scale for geothermal development in the Qinghai Gonghe Basin. The results indicate that the compressive strength and elastic modulus of Gonghe granite increase with temperature up to 200 ℃ due to the enhancement of mineral mechanical properties and thermal densification, but significantly decrease at 300 ℃ due to thermal damage and fracture propagation. Energy analysis reveals that the granite undergoes a transition from brittle to ductile behavior under high-temperature conditions. The proportion of energy dissipation during deformation increases with temperature. The increased proportion of quartz, coupled with its high thermal expansion coefficient and elastic modulus, generates intense thermal stress at the interfaces between quartz and adjacent minerals. The development and propagation of transgranular fractures around quartz are critical factors influencing the macroscopic mechanical properties of granite. This study provides a good understanding of the effects of high temperature on granite performance and its engineering significance in reservoir development, emphasizing the role of thermal stress in reducing fracturing pressure and promoting fracture propagation.

Liquid nitrogen (LN₂)-assisted fracturing has emerged as a promising technique to enhance the productivity of hot dry rock (HDR) geothermal reservoirs. To elucidate the progressive mechanical degradation and fracture mechanisms of granite under cyclic thermal shocks, this study integrates ultrasonic testing, acoustic emission (AE) monitoring, three-dimensional profilometry, and uniaxial compression testing. Damage evolution was assessed through velocity attenuation, waveform distortion, and AE characteristics, while microcrack propagation and fracture morphology were analyzed using scanning electron microscopy and surface topography reconstruction. The degradation process exhibits a distinct cycle-dependent transition, evolving from tensile microcrack initiation during early cycles to shear-dominated failure during prolonged cycling. In Phase Ⅰ (1-3 cycles), initial thermal stresses induce axial tensile microcracks, leading to sharp decreases in P-wave velocity (53.45 %) and amplitude (40.55 %). Frequency analysis reveals a narrowing and convergence of secondary bands, whereas the fracture surfaces exhibit low undulation, dominated by tensile failure. In Phase II (3-20 cycles), shear-dominated damage progressively develops, as cyclic cooling enhances crack connectivity. AE activity intensifies sharply, correlating with macroscopic shear crack networks. Fracture surfaces evolve toward step-like morphologies, with roughness parameters increasing by up to 277.43 %, indicative of composite tensile-shear failure. Cyclic LN₂ cooling significantly lowers crack initiation stress and fracture energy, while promoting crack density and surface roughness. These findings provide critical insights into the mechanisms of LN₂-induced fracture enhancement, highlighting its potential to optimize HDR reservoir stimulation strategies.

Current in-situ stress determination methods are typically conducted inside a drillhole after its creation. However, the drilling process itself is not utilized for measuring in-situ stress or rock strength, despite being a form of direct mechanical testing on the rock mass. Crucially, drilling contains valuable information about in-situ stress and rock strength, as rocks under high compressive stresses exhibit greater strength. This paper presents a novel in-situ stress determination method, supported by the experimental result of rock drilling monitoring tests using a mine hydraulic-rotary drilling machine. Key drilling parameters-including thrust force, rotation speed, torque and drilling speed-are monitored in real time to determine the drilling specific energy per unit volume of rock. A concave-upward relationship between drilling specific energy and rotation speed is identified, which can characterize rock compressive strength and tensile strength with consistent regularity. Further drilling tests are conducted on the same rock samples under varying confining pressures. Results indicate that as confining pressure increases, the concave-upward curve of drilling specific energy shift upward, reflecting enhanced rock strengths due to confinement. The paper outlines the complete methodology for in-situ stress determination using drilling monitoring techniques, bridging the research gaps among drilling monitoring, rock mechanics, and in-situ stress analysis.

This study integrates unconfined compression tests with high-resolution computed tomography (CT) to analyze the pore heterogeneity, crack propagation, and failure modes of red sandstone specimens with diameters ranging from 10 mm to 100 mm. Key findings include: (1) With increasing specimen size, crack initiation stress (CI), damage stress (CD), and unconfined compressive strength (UCS) initially increase and then decrease, (2) In smaller specimens, stress concentration due to pore heterogeneity leads to splitting failure and lower strength, (3) In medium-sized specimens, friction dominates crack propagation, causing shear failure, while increased fragment rotation enhances energy dissipation, yielding highest strength, and (4) In larger specimens, cracks tend to propagate along bedding planes, reducing energy dissipation and then weakening strength. These results provide insights into the reverse size effect on sandstone strength and have implications for engineering applications.

Hazardous geophysical granular flows, such as debris flows and rock avalanches, can exert intense impact forces on obstacles and threaten downstream structures located in their paths. Installing protective structures can mitigate damage, but quantifying their influence on flow evolution and impact loading remains challenging. This study investigates the interactions of granular shock waves (GSWs) generated in front of two cylindrical obstacles with varying spacings through chute experiments and discrete element modeling. Impact pressure sensors were mounted on the upstream surface of each cylinder and on the chute bed to measure dynamic impact pressures in the GSW region. Granular flow velocity and depth were obtained using image processing. Results demonstrate that cylinder spacing significantly influences the geometric characteristics of GSWs. Runup increases with steady-state Froude number (Fr_steady) but decreases as spacing narrows. The granular vacuum length grows with bed slope but decreases significantly with decreasing cylinder spacing. Impact pressures on the cylinders and the chute bed increase linearly with Fr_steady. Low-frequency power spectral density (PSD) is positively correlated with Fr_steady, whereas centroid frequency and pressure impulse counts exhibit low sensitivity to Fr_steady. The dimensionless impact pressure coefficient (α) decreases nonlinearly with increasing Froude number (Fr). At low Fr, α values for dry granular flows are lower than those for debris flows, but the difference diminishes at higher Fr. These findings may improve our understanding of granular flow-obstacle interactions and might help to design protective structures.

Thermal cycling and stress fatigue are recognized as principal factors that induce the Kaiser effect of rock in deep earth rock engineering. Nevertheless, existing scholarly investigations about the mechanical properties of rocks subjected to the synergistic effects of these perturbations have remained insufficient. In this study, conventional triaxial compression tests, multistage equal-amplitude fatigue (MEF) and multistage variable-amplitude fatigue (MVF) tests were conducted on marble subjected to different numbers of thermal cycles, integrated with nuclear magnetic resonance (NMR) and depth-sensing indentation (DSI) micro-monitoring methods, and the rock constitutive equation was established from the perspective of statistical microscopic damage. The results indicated that the increasing number of thermal cycles significantly weakened the physical and mechanical properties of marble, as evidenced by degradations in strength, deformation, and energy parameters. The reversible deformation evolutions of the rock under two stress paths were diametrically opposed. DSI results revealed that the microcellular mechanical parameters of hornblende and dolomite exhibited greater variability, although both conform to Weibull distribution functions. Additionally, NMR analysis showed that the porosity of the marble was 1.6% initially and increased to 3.3%, 4.1%, 5.8%, and 10.9% after 2, 4, 6, and 8 thermal cycles, respectively. The coupled thermal-mechanical damage constitutive model can effectively describe the deformation behavior of marble under complex perturbations, with distribution parameters m₀ and T₀ decreasing linearly with the number of thermal cycles.