International Journal for Numerical and Analytical Methods in Geomechanics最新文献

The shear behavior of intermittently jointed rock masses is crucial in engineering geology, yet the widely used Jennings criterion still lacks a systematic evaluation regarding its accuracy when applied to rock with various joint geometries. This study combines physical experiments and Particle Flow Code (PFC) simulations to investigate how joint geometries influence shear strength and to further assess whether the Jennings criterion can effectively capture these influences. Both approaches reveal similar trends: peak shear stress and cohesion decrease with higher joint connectivity and number, but increase with steeper dip angles. In the present experimental conditions, no clear trend was observed between the friction angle and variations in discontinuity geometrical features, which is likely related to the relatively limited range of geometrical configurations considered in the tests. A further comparison between measured and Jennings-derived equivalent cohesion shows a widespread discrepancy: on average, equivalent cohesion exceeds measured values by 31.4% in physical tests and 10% in numerical simulations. This overestimation, due to stress concentration and altered failure paths introduced by different joint geometries, is most significant in low-connectivity, high-joint-number, and gentle-dip-angle scenarios. These findings suggest that the Jennings criterion's applicability is limited, as significantly overestimated equivalent parameters could lead to overly optimistic stability assessments under certain conditions. Additionally, the impact of joint geometrical features on shear strength is both systematic and potentially quantifiable, offering a valuable reference for incorporating such features into equivalent parameter estimation methods to improve the accuracy of strength assessments.

Discontinuous deformation analysis (DDA) is a numerical method that is extensively utilized for simulating discrete blocks. Nevertheless, its implicit calculation approach brings in a multitude of control parameters that lack physical significance, and proper handling of these parameters is essential for obtaining accurate results. To tackle this issue, this study proposes a surrogate model-driven parameter calibration framework that incorporates interpretability analysis. First, a Kriging surrogate model is constructed to establish an efficient substitute for DDA computations, thus accelerating forward calculations. Subsequently, the SHapley Additive exPlanations (SHAP) method is introduced to quantify global parameter sensitivity. Finally, an intelligent optimization algorithm is integrated to develop a parameter inversion mechanism, thereby forming a complete calibration system of “surrogate modeling–sensitivity analysis–parameter optimization.” Numerical examples demonstrate that this framework can effectively identify the optimal combination of key control parameters. The average errors are 1.39% in the two-slider model and 1.63% in the elastic foundation model. This approach offers an automated parameter calibration process that doesn't require manual intervention, providing a reliable theoretical tool for DDA engineering applications in tunneling, slope stability, and rock engineering.

Debris flows, characterized by a heterogeneous mixture of solid, liquid, and gas phases, exhibit complex mechanical behavior and pose substantial threats to infrastructure and human lives in mountainous regions. This study presents a novel three-dimensional material point method (MPM), integrating a geographic information system (GIS) and Perlin noise functions, to model the debris flow over complex terrain as a coupled liquid-solid system. The digital elevation models in GIS are mapped directly onto the MPM computational domain and preserve realistic terrain features. The irregular rock blocks generated by Perlin noise function in Houdini software are embedded into the source zone of debris flow to explicitly represent fluid-solid interactions. In addition, to maintain the computational accuracy and efficiency, the sparse paged grid structure (SPGrid) is introduced to provide an efficient computational framework for large-scale 3D hazard analysis. The proposed MPM framework is validated firstly by comparing numerical results and experimental data from previous studies, including saturated soil leakage, rockslide-induced wave generation, and debris dam break flow. The dynamic behavior and deposition patterns of debris flows are then analyzed, revealing that these factors are significantly influenced by rock block content and the basal friction coefficient. Results show that the proposed two-phase two-point MPM is an effective tool to reproduce the realistic propagation of debris flows and provides a scientific reference for hazard assessment and disaster prevention in debris flow-prone regions.

The study of water retention and strength characteristics in unsaturated soils is an underexplored topic yet significant challenge in geotechnical engineering. This paper proposes a simplified computational model for the soil-water characteristic curve (SWCC), incorporating the novel proposed void optimization parameters l₁and l₂. This model can predict SWCC under various initial void ratios and is applicable across a wide suction range. Additionally, we suggest an adjustment parameter m, which can reflect soil type, and then develop a three-dimensional strength criterion for unsaturated soil. The strength criterion inherently allows for three expansion trends of the failure surface as the matrix suction s increases: parallel, outward non-parallel, and inward non-parallel. Furthermore, based on the novel SWCC model, a predictive formula for the shear strength q_f of unsaturated soils is established. This formula is then applied to accurately estimate the strength of unsaturated soils under drained true triaxial conditions.

This research investigates the time-dependent damage deformation of granular rock using a grain-scale stress corrosion (GSC) modeling approach. Stress corrosion, originating from damage within the grains and along the grain boundaries, is considered the main mechanism causing weakening and time-dependent damage of granular rock. To account for the microstructure geometry of rock, the parallel-bond stress corrosion (PSC) model is extended to a grain-based model (GBM) within the Particle Flow Code (PFC). Accordingly, the modeling parameters are calibrated against data from uniaxial compression and fatigue tests on Lac du Bonnet granite. The numerical modeling results show that the long-term strength and failure time of granular rock increase prominently with the increase of confining pressure and the decrease of the driving-stress ratio. The number of microcracks along the grain boundaries is far more than that within the granule interior. Grain crushing, which is traced by granule interior microcracking, appears in specimens with high confining pressures. It is found from the simulation results that the damage in the failed specimens caused by long-term loading, both inside the grains and along the grain boundaries, is less than that caused by short-term loading. The results also show that stress corrosion within the granule interior significantly influences the time-dependent behavior of granular rock under high driving-stress ratios, whereas stress corrosion along the grain boundary becomes dominant under low driving-stress ratios.

Investigating the cumulative thermal damage of rocks under prolonged high-temperature exposure is crucial for the stability of deep rock engineering. This study investigates the temporal effects of thermal exposure (1–32 h) on granite's physico-mechanical properties and damage mechanisms through experiments at 150°C, 550°C, and 950°C, combined with uniaxial compression tests, acoustic emission (AE), and numerical simulation. The results show that: (1) the mass loss rate, volume expansion rate, P-wave velocity reduction rate, and porosity increase exponentially with the duration of high temperature. The proportion of large pores increases. (2) Uniaxial compressive strength and elastic modulus decay exponentially, while peak strain grows exponentially. AE dominant frequency shifts from 120–140 kHz to 260–320 kHz, reflecting microcrack-dominated fracture. (3) Numerical simulations show thermal crack density positively correlates with temperature/duration. Over 80% of cracks are intergranular shear fractures, with orientations transitioning from directional to random, accompanied by brittle-to-ductile failure mode evolution. (4) Microscopic analyses identify mineral phase transitions, grain-boundary cracking, and interconnected pores as primary damage mechanisms, where temperature governs physico-chemical reactions and duration amplifies cumulative damage. This work provides reference and suggestions for evaluating the long-term thermal stability of rocks in deep, high-temperature geotechnical engineering applications.

To well understand the crack evolution and failure mechanisms of strain rockburst, the present study simulated the rockburst processes under nine unloading rates. A discrete element grain-based model (GBM) was adopted, coupling with acoustic emission (AE) monitoring. The results show that the unloading rate minimally affected the overall fracturing sequence: initial micro-tensile crack dominance, followed by accelerated micro-shear crack growth, leading to macro-fracture formation. However, rock strength exhibits a non-monotonic dependence on unloading rate, decreasing rapidly initially and then gradually increasing. This strength fluctuation correlates strongly with a rapid decrease followed by a gradual increase in the proportion of intragranular micro-cracks (tensile and shear). Furthermore, under low unloading rates, the failure mode is mainly shear macro-fractures without V-shaped pits, and it transits to pronounced V-shaped pit formation under high unloading rates. As the rate increases, the specimen failure mode changes from tensile-dominated to shear-dominated strain rockburst. Throughout rockburst process, the proportion of tensile failure in AE events gradually decreased but remained the dominant micro-failure mode. The onset of rockburst is consistently marked by a sharp increase in AE events associated with compaction failure. Notably, a distinct AE “quiet period” precedes rockburst initiation at low unloading rates; this quiet period diminishes and becomes less probable as the unloading rate increases.

Further investigation into the evolution of soil arching influenced by initial anisotropy remains essential. In this study, the discrete element method is employed to analyze trapdoor models with varying degrees of initial anisotropy, which are calibrated using data from previous experimental studies. The results indicated that the overall trend of the ground reaction curves remains consistent across samples with varying initial bedding angles, with three distinct stages. The variation in the ultimate soil arching ratio closely parallels that of the minimum ratio, also exhibiting an approximately symmetric “M”-shaped pattern, with the minimum value occurring at θ = 45°. Compared with isotropic spherical materials, anisotropic materials show a weaker soil arching effect. The evolutionary pathways of soil arching can be categorized into two distinct patterns: the quasi-symmetrical arch and the deflection arch. The dominant direction of force chains progressively aligns with the imposed bedding angle. Increasing the initial bedding angle leads to progressively more concentrated contact force distributions and increasingly robust force chain structures. The distribution of normal forces, tangential forces, and contact number is strongly influenced by the initial bedding angle.