The long-term stability of pumped-storage reservoir banks is strongly governed by damage evolution induced by prolonged water immersion. In this study, reservoir bank sandstone from the Laowuji pumped-storage site in Guizhou, China, was examined using computerized tomography (CT), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and molecular dynamics (MD) simulations to systematically characterize damage evolution from the mesoscopic to microscopic scales and to elucidate cascade effects across multiple scales. After 360 days of immersion, the mineral cement interface dissolution area increased from 12.51 mu m2 to 139.83 mu m2. Porosity rose from 9.45 % to 10.95 %, the small-pore fraction decreased to 80.11 %, and medium-tolarge pores increased significantly, enhancing pore connectivity and heterogeneity. Concurrently, the P-wave velocity decreased cumulatively by 45.99 %, indicating a high sensitivity to microstructural degradation. MD simulations revealed that mineral interfaces weaken chemical bonding while providing lubricated and dilatable pathways, thereby facilitating early microcrack initiation and rapid propagation, ultimately compromising reservoir bank integrity and reducing seepage safety margins. The three-dimensional fracture spatial inhomogeneity index (FSI3D) increased by more than an order of magnitude over 360 days, capturing the transition of fracture patterns from relatively simple through-going cracks to a complex, interconnected fracture network. On this basis, a zoned management strategy consisting of "shallow-sealing and deep-infiltration control" and a multi-parameter dynamic early warning system is proposed. These findings provide theoretical support and engineering guidance for long-term stability control of reservoir bank sandstone in pumped-storage systems.

This paper proposes a novel Anisotropic Lattice Spring Model (ALSM) to address the limitations of traditional LSMs in simulating anisotropic deformation of layered rocks such as schist, shale, and slate. The model introduces two key innovations: (1) normal-tangential coupled spring bonds that form a full stiffness matrix with non-zero off-diagonal terms, overcoming the inherent Poisson's ratio constraints of LSMs; and (2) a dual-constraint stiffness matching method that incorporates stress symmetry into the energy equivalence framework, ensuring physical consistency in macroscopic constitutive relations and enabling prescise mapping between microscopic parameters and macroscopic elastic constants. Verification results show that the ALSM significantly broadens the achievable range of Poisson's ratios and accurately simulates strongly anisotropic rocks. In uniaxial compression and Brazilian disc tests, the ALSM yields apparent elastic moduli consistent with theory/experiment, captures non-monotonic anisotropy, and markedly reduces displacement/stress errors compared to traditional models. The model allows direct input of macroscopic anisotropic parameters, avoiding complex microscopic calibration. The established elastic homogenization framework supports further study of anisotropic fracture and offers a new approach for bottom-up design of anisotropic materials.

Accurate characterization of the mechanical strength and fracture evolution of anisotropic shale is essential for constructing complex fracture networks during hydraulic stimulation of shale gas reservoirs. In this study, a discrete element method (DEM)-based thin-layer numerical model is established to reproduce the laminated mineral fabric of shale. The inherent structural anisotropy of shale is reflected by its stratified architecture, while mechanical anisotropy is captured via differentiated mesoscopic parameters for matrix and bedding layer particle bonds. Numerical Brazilian tests results indicate that: The maximum principal stress concentrates mainly around the specimen center, and its spatial distribution is strongly governed by bedding layer orientation. Mesoscopically, cracks propagate along stepped trajectories, which arise from breakage of weaker matrix and bedding layer and ultimately produce distinct macro-fracture morphologies. To quantitatively characterize bedding layer weakening effects, an interface strength weakening coefficient (ISWC) is proposed. A series of parametric simulations demonstrate that both tensile fracture patterns and normalized tensile strength are highly sensitive to ISWC and bedding layer orientation. Moreover, the coupling relationship between failure mode, ISWC and bedding angle is clarified under Brazilian indirect tension loading. The study deepens the fundamental understanding of fracture mechanisms in laminated shale and provides quantitative references for optimizing hydraulic fracturing schemes in shale gas engineering.

Layered rocks exhibit anisotropic deformation key to geotechnical stability. This study develops a novel Anisotropic Lattice Spring Model (ALSM) within a Discrete Element Method (DEM)-compatible unified discrete framework. It addresses two key bottlenecks: difficult macro-micro parameter mapping and the inherent Poisson’s ratio limitation of traditional LSM. Innovations include: (1) a Dual-Constrained Stiffness Matching and Superposition Method for precise mapping from macroscopic anisotropic constants to microscopic spring parameters, enabling direct field data use; and (2) an Adaptive Poisson’s Ratio Release Technique, removing Poisson’s ratio limits via local average strain rate to robustly simulate high Poisson’s ratio materials on arbitrary meshes. The model is validated through benchmarks, confirming its accuracy in replicating anisotropic apparent elastic moduli and achieving FEM-level displacement and stress field reconstruction. This work elevates irregular-lattice ALSM accuracy to match irregular-mesh FEM. Crucially, the model establishes a DEM-compatible particle-spring framework, sharing the core architecture (particle-based representation and explicit dynamic solution) with DEM, thereby paving a natural and efficient pathway for integrated continuous-discontinuum analysis of anisotropic rocks.

In geotechnical systems, the seepage direction often deviates from the gravity direction, potentially altering erosion mechanisms in soil–rock mixtures (SRMs). This study systematically investigates the internal erosion behavior of gap-graded SRMs under varying fine contents (FC = 20

This study introduces a discrete element numerical simulation method for calcareous sand particles that incorporates a dual-porosity and allows for the quantitative generation of internal pores. The method is designed to capture three key distinguishing characteristics of calcareous sand compared to quartz sand: the abundant dual-porosity, pronounced particle aspect ratio and high susceptibility to breakage. Biaxial tests are simulated across various confining pressures to explore the effects of different particle fragmentation states, as well as the impact of internal and external pores on the shear strength of the sample. The findings of this study offer significant academic insights into the strength and fragmentation mechanisms of calcareous sand, thus contributing to the broader understanding of granular materials in geotechnical engineering and related fields.

Multiscale degradation and early warning studies of weathered rock in cold regions are limited. This study investigates the evolution of mineral composition, pore structure, and physico-mechanical properties of weathered granite using mineralogical analysis, low-field nuclear magnetic resonance (NMR), mechanical testing, and acoustic emission (AE) monitoring. A multiscale degradation correlation mechanism linking microcracks, mesoscopic pores, and macroscopic properties was established based on Pearson correlation analysis. Based on critical slowing down (CSD) theory, the early warning characteristics of AE parameters were analyzed, revealing a correlation between recovery rate (λ) and brittleness index (BI). Results indicate that weathering alters the mineral composition and pore structure of granite, resulting in decreased mass, volume, P-wave, uniaxial compressive strength, and elastic modulus, while both permeability coefficient and maximum strain increase. Porosity increased from 0.13 to 4.01

This study employs three-dimensional (3D) discrete element method (DEM) simulations of triaxial tests conducted under membrane boundary conditions to explore the shear behaviour of binary soil mixtures characterised by stratification. Various binary mixture samples were meticulously prepared with diverse gradations and particle size ratios (PSRs), and their shear strength and volumetric strain were examined from both macroscopic and microscopic perspectives. The findings demonstrate the substantial influence of PSRs associated with stratification on the behaviour of geotechnical binary mixture samples, while suggesting a relatively modest effect of the sequence of coarse and fine particles. On a microscopic level, force chains within the coarse particle layer were predominantly coarse and characterised by wide spacing, while those within the fine soil layer were fine and densely packed. The findings aid landslide prevention by identifying interlayer interfaces as potential failure zones, high PSR between layers (>4.0) may weaken shear strength of stratification.

Investigating the failure pattern and mechanism of shale is significant for shale gas exploration. Shale specimens with horizontal bedding planes are tested under indirection tensile stress, and a high-speed camera monitor is synchronously conducted for digital image correlation (DIC) calculation. The results show that, the shale specimens may fail at loading points or other weak points, leading to a planar curve on the front surface. Different loading rates and bedding planes contribute to torque and bending moment on the cross-section, resulting in a torsional space fracture surface. Finally, a 3D numerical model was established to reappear the failure morphologies. The fracture mechanics are revealed from the energy conversion perspective. The study can provide some references for the study of the three-dimensional fracture model and mechanism of rock in geotechnical engineering.

Weakly cemented sandstone is softened by water erosion, which increases the water content and seriously reduces the bearing capacity of the surrounding rock. In this paper, a numerical model is developed based on the bond contact state of the parallel bond model, which takes into account the macroscopic strength deterioration and pore space increase caused by the microscopic disbonding effect of the weakly cemented sandstone under water erosion, and introduces it into the computational fluid dynamics-discrete element method coupled fluid-solid method. In addition, the permeability evolution equation due to particle loss under erosion was established based on the Kozeny-Carman equation considering the clay-bearing effect. The sand inrush process of weakly cemented sandstone strata under different water levels was simulated. The results show that there is a hysteresis phenomenon of sand inrush with weakly cemented sandstone strata. The evolution of the sand inrush process usually consists of four stages: the erosion stage by disbonding; the erosion stage by flushing and disbonding; the upper-stratum collapse phase; and the continuous large deformation stage. As the water level lowers, the maximum height, length, and width of the collapsed area within the strata decrease dramatically. The increment of the supporting structural force also decreases, which reduces the risk of cracking of the tunnel support structure. The results of this study can be used as a scientific basis to study the prevention and control of sand inrush disasters in tunnel construction in water-rich weakly cemented sandstone strata.

In this study, an ABAQUS-PFC3D coupling program framework based on the Computational Fluid Dynamics (CFD)-Discrete Element Method (DEM) coupled fluid-solid analysis method is constructed, which can be run in Windows computer system and Python language environment, and takes into account the high efficiency, simplicity, and computational stability of the bi-directional interaction of fluid-solid field information. The coupled program framework is validated using a classical particle-fluid coupling model case to assess its stability and accuracy. Further, the ABAQUS-PFC3D coupling program is used to study the evolution characteristics of internal erosion of gap-graded soil-rock mixtures of different fines contents (indoor test scale) and reproduce the whole process of water and mud-surge disaster in the Yonglian water-rich fault tunnel in Jiangxi, China, including the disaster-causing stages of palm collapse, accumulation of broken rock inside the tunnel, collapse within the fault, and surface collapse (engineering scale). The results show the stability of the coupling program framework, which improves a good reference for the popularization and application of the CFD-DEM fluid-solid coupling model.

In acidic environments, rock masses are frequently subjected to severe chemical corrosion, resulting in the initiation of numerous geological engineering disasters. This study aimed to collect physical and mechanical parameters of granite exposed to prolonged acid corrosion and analyze fracture characteristics using acoustic emission (AE) techniques. Additionally, it examined the evolution of pore structure and damage mechanisms through the use of low-field nuclear magnetic resonance (NMR) and fractal theory. The results demonstrate a monotonic decrease in mass, volume, density, P-wave velocity, and S-wave velocity of granite with increasing corrosion time. Particularly notable is the phased reduction observed in uniaxial compressive strength and elastic modulus. The transition from brittle to ductile failure in corroded granite is accompanied by a gradual decrease in internal fracture strength. The trend in the correlation dimension reveals the relationship between the formation time of the main fracture surface and the pore structure. Additionally, total porosity and macropores (D, Da) exhibit significant fractal characteristics. The fractal dimension correlates positively with the damage variable and inversely with uniaxial compressive strength and elastic modulus. This indicates that more severe pore structure damage leads to a higher fractal dimension and lower mechanical performance. Among these, Da demonstrates higher sensitivity in characterizing rock mechanical properties. These findings provide important basis for evaluating the stability of granite geotechnical engineering in acidic environments.

Landslide movement processes often exhibit complex paths, introducing the uncertainty of landslide movement paths, and challenging landslide hazard prediction and pre-disaster prevention and control. In this study, we employed numerical simulations to investigate the dynamic processes with complex paths of the Pangjiawan landslide using the 3D discrete element method. A scenario simulation was conducted to evaluate the stability of the landslide, incorporating arched anti-slide piles, and the reinforcing effect of arch anti-slide piles on the Pangjiayan landslide under different rise-span ratios and pile spacing was analyzed in depth. The results indicate that the Pangjiawan landslide in mountainous notch topography exhibits a complex movement path with turning and convergence behaviors, and arched anti-slide piles are more effective in stabilizing the landslide than traditional linear anti-slide piles. When the embedded depth of the arched anti-slide piles remains consistent, higher rise-span ratios result in more significant synergistic effects between the piles and the surrounding soil. Moreover, even with increased pile spacing and a reduction in the number of anti-slide piles, the landslide displacement after reinforcement with arched anti-slide piles is lower than traditional linear anti-slide piles. The research provides valuable insights into the dynamics of landslide movements, emphasizing the superior reinforcement capabilities of arched anti-slide piles. This contributes to our understanding of landslide mitigation strategies in challenging topography.

<p>The key to increasing shale gas production is to construct fracture networks in shale reservoir to provide channels for shale gas. Understanding the cracking characteristics of shale is necessary for oil and gas exploitation engineering. Given this, uniaxial compression tests were conducted on Longmaxi shale in China to study the mechanical properties and cracking behaviors affected by bedding layers and pre-existing slot. Sandstone specimens with different pre-existing slot angles were also tested as a comparison. A mechanical-optical-acoustical comprehensive data acquisition system consisting of a rigid hydraulic machine, high-speed industrial camera and acoustic emission acquisition instrument was established to monitor the cracking behaviors in real time. The results show that the cracking behaviors of shale specimens are quite different from sandstone specimens in the uniaxial compression tests. Crack initiation is predominantly controlled by the pre-existing slot and is also affected by bedding layers. Crack propagation is mainly controlled by bedding layers and stress field distribution. When the bedding layers are vertical, the cracks are most likely to propagate along the direction of the bedding and tensile cracks are observed. When the bedding is 30°, the shale specimens are most likely to be controlled by the bedding layers, resulting in shear slip failure along the bedding layers. The experimental results contribute to the understanding of cracking properties in layered anisotropic materials.</p>

Investigating the relationship between water contents and the dynamic response of soil cut slopes under the action of train loading is beneficial to slope safety assessment. The effect of water contents on dynamic response characteristics and the potential failure mechanism of the slope under cyclic loading was investigated using geotechnical model tests and numerical calculations. It was found that a slope with higher water content showed a larger vibration intensity. The main effect of heavy-haul train loading on the slope was always concentrated in the slope foot or the shallow depths. As the propagation distance increased, the far-field vibration was mainly low frequency. Dynamic stress from the train loading was much larger close to the slope foot, and it was prone to forming a localized low-reliability zone with higher water content at an early time. As the water content increased, the development scope of the potential sliding surface tended to extend into the slope, which can lead to slope failure ahead. Also, the shear strain increment caused by two passing trains was more than that by a single passing train, which showed no obvious periodicity with random fluctuations significantly. In addition, a dynamic strength reduction method to calculate the safety factor of the soil slope under train cyclic loading is proposed to evaluate the slope stability better.

<p>This research aims to study the deformation and fracture behavior of shale by a novel anisotropic regular lattice spring model (ARLSM). The novel ARLSM applies the normal and tangential coupling spring to release the Poisson's ratio limitation in the traditional regular lattice spring model. Meanwhile, a nonlinear strength criterion is introduced into ARLSM to simulate the fracture failure of shale. Two benchmark problems are tested to implement the research. The study shows that ARLSM has larger range of Poisson's ratio and better effects comparing with the existing anisotropic lattice spring model. Moreover, ARLSM can accurately predict the deformation and fracture behavior of shale under different conditions.</p>

This study developed a new model, a 3D coupled computational fluid dynamics (CFD)-discrete element method (DEM) model, by coupling two software programs, ABAQUS and PFC3D, to solve problems related to fluid-solid interaction systems. The complete governing equations and the two-way coupling process between the two software are presented herein. Via Transmission Control Protocol (TCP) socket communication with Python scripting, information between the two software is exchanged in real-time. Then, the classic example in the PFC5.0 documentation was used to verify the model. In the end, the ABAQUS-PFC3D model was employed to simulate the process of water and mud inrush in a water-rich fault tunnel, which could reflect the evolution process of water and mud inrush and track particle movement in a fault zone. The results show that the particles that collapsed inside the fault formed an ellipsoidal distribution during the water and mud inrush in a water-rich fault tunnel. With the continuous loss of particles in the fault into the tunnel, the migration of particles is discontinuous, and a large void appears inside the fault zone. The rapid change of the groundwater flow velocity caused the negative pore pressure. The pressure arch force structure is formed above the ellipsoidal collapse area inside the fault. The principal force field of the fault areas changes from close to the dip of the fault to close to the perpendicular to the fault.

This research paper presents an investigation into the shear behavior of binary mixtures composed of cubic and spherical particles, employing the discrete element method (DEM) through triaxial tests simulations. A range of binary particle samples with varying volume fractions of cubic and spherical particles is generated for analysis. The study primarily focuses on examining the contracting-dilatancy relationship of binary granular material samples by scrutinizing deviatoric stress and volumetric strain curves, while considering the influence of confining pressure, initial porosity, and particle size ratio. Furthermore, the paper sheds light on the evolution of microstructures during the shearing process by presenting coordination numbers and rotational velocity fields for different particle types (overall particles, cubic particles, spherical particles), as well as between cubic-spherical particles. The findings demonstrate the substantial impact of both the volume fraction of cubic particles and the particle size ratio on the shear behavior of binary particles at both macroscopic and microscopic scales. Additionally, a comprehensive investigation reveals the dependence of anisotropy in normal contact forces, tangent contact forces, and contact orientations on the volume fraction of cubic particles.

A seepage testing system was designed and a series of seepage experiments on broken rock was conducted using different original porosity conditions and clay contents. The mass-loss process of the broken rock and the change in water flow velocity were investigated. After the mass-loss test, the non-Darcy seepage characteristics of the broken rock were tested through a step-by-step pressure-reduced seepage test. The experimental results show that the mass-loss and water velocity evolution during the water inrush could be divided into four stages: acceleration, stable with slight fluctuations, reacceleration, and stable. The lost-mass and change in water velocity were positively correlated with the clay contents and negatively correlated with the original porosity. By introducing the evolution equation of the Kozeny-Carman equation and the liquid limit index which characterises the effective particle size, the prediction model of the permeability coefficient was built. Six prediction models of the non-Darcy coefficient were verified against the testing results. The prediction model of the critical flow velocity from a Darcy flow to a non-Darcy flow using the Forchheimer number was also established. The results could provide an important reference for understanding water inrush mechanisms, adopting effective control measures for water inrush events, and calculating the water influx of tunnels.