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

High hydraulic gradients induced by initial water filling in diversion tunnels with permeable linings or sudden fluctuations in total head inside the tunnels trigger transient seepage in the surrounding soils. Although this transient flow helps relieve excess pore pressure, it also leads to significant ground deformation, variations in in-situ stress, and expansions of the plastic zone around the tunnel. This effect is especially produced in deep tunnels embedded in low-permeability soils, where the transient flow process may be prolonged and have a substantial impact on the local stress-strain environment. This study presents an analytical solution for characterizing transient seepage around deep tunnels by employing the superposition principle and the method of separation of variables. A seepage stress potential function is introduced to analyze the variations in soil responses and plastic stress evolution under high in-situ stress conditions based on the Mohr–Coulomb failure criterion. The results show that stress, strain, and displacement within the soil are proportionally related to the total head difference between the tunnel interior and the surrounding ground. Specifically, rheological soil behaviors accelerate the transient seepage process. The plastic zone, influenced jointly by transient seepage and in-situ stress, undergoes significant development before stabilization. The proposal analytical solution provides a rigorous and highly efficient tool for evaluating the operational environment of diversion tunnels and supports their safe and effective designs and maintenance.

Random field modelling is widely used in geotechnical reliability analysis, as the relevant properties of soil and rock often exhibit significant spatial variability. The Karhunen–Loève expansion (K–L) has gained popularity as a method for generating random fields involving the decomposition of covariance structures into an infinite series of orthogonal eigenfunctions. In practice, this series needs to be truncated after a finite number of terms due to computational constraints. K–L truncation is directly controlled by the domain size, correlation length and spatial grid size on which the random field is to be generated. Truncation results in discretisation errors in the random field generation, which must be carefully managed. This paper reviews the principles of K–L, its implementation for random field generation, and its use in a geotechnical context. The presence of streakiness and checkerboard effects as observed by some investigators using K–L is critically examined. An example of a finite element geotechnical stability problem using K–L generated random fields is presented, highlighting the possibility of distinctly different failure mechanisms depending on the level of truncation employed in the K–L random field generation.

Dynamic analysis of tunnels under blast-induced waves is crucial in civil engineering. Previous studies have often treated incident waves as plane waves, which may not be appropriate for the scenario of a wave source near the tunnel. In this study, the scattering of a tunnel in a saturated medium by cylindrical P- and SV-waves is investigated. Based on the wave function expansion method, the displacement, velocity, pore pressure and stress fields over the substrate are determined. Some important quantities, including the dynamic stress concentration factor (DSCF), hoop velocity scaling factor (HVSF) and radial velocity scaling factor (RVSF), are evaluated and discussed. Numerical examples are carried out to discuss the effects of seepage boundary condition, type of incident wave, distance of the wave source and wave frequency on the distributions of DSCF, HVSF and RVSF. It is seen that the DSCF pertinent to the impermeable boundary condition is larger than the counterpart under the permeable boundary condition. In addition, the DSCF induced by the plane P-wave may be smaller than that by a cylindrical P-wave at low frequencies. This research is valuable for evaluating the safety of underground facilities under blasting waves.

Shale, a sedimentary rock with significant heterogeneity and well-developed bedding structures, exhibits complex mechanical behaviors and failure mechanisms. In this study, the Discrete Element Method (DEM) is employed to develop a Weibull distribution-based parameter assignment approach for simulating heterogeneous shale specimens under uniaxial compression. The mechanical responses and fracture evolution are systematically analyzed, and a novel damage constitutive relation is proposed that accounts for both material heterogeneity and bedding structure effects. The results show that: (1) the stress-strain curves consist of three stages: linear elasticity, nonlinear crack propagation, and brittle failure. The peak strength follows a power–law relationship with the homogeneity index (m), and at higher homogeneity levels (m ≥ 8), enhanced stress uniformity delays post-peak stress reduction. At a 90° bedding angle, the mechanical response transitions to bedding-plane-dominated ductile deformation, with reduced sensitivity to homogeneity. (2) The failure mechanisms are governed by dual control effects: at bedding-dominated angles (60°–90°), tensile fracturing along bedding planes predominates and is weakly affected by homogeneity, while at co-controlled angles (0°–45°), failure patterns evolve with increasing m, progressing through V-shaped, inverted V-shaped, and oblique L-shaped fractures. (3) Stress-strain curve fitting using the proposed damage constitutive relation demonstrates strong consistency with simulation results for m > 2. These findings provide a quantitative framework for assessing damage thresholds in shale with varying homogeneity and bedding angles, offering valuable guidance for shale-related engineering projects.

This study presents an innovative approach to simulating brittle rock behavior under unloading conditions using an improved discrete element method (DEM) that incorporates the particle interlocking effect. By expanding the interaction range between particles, the model enhances the pressure ratio and internal friction angle of the rock, overcoming the limitations of traditional DEM models in simulating the nonlinear failure envelope of brittle rock. A weighted Delaunay triangulation technique is employed to discretize the rock medium, enabling a more refined mesoscopic-scale representation. A coupled discrete element method–porous finite volume (DEM–PFV) solid–fluid interaction model is then developed to simulate the fluid flow through fractured rock, offering a more accurate depiction of solid–fluid interactions at the microscopic scale. The study explores the effects of different initial axial pressures, confining pressures, water pressures, and fracture angles on the deformation, strength, fracture, and propagation of brittle rock under unloading conditions. Additionally, it investigates the flow and damage mechanisms of fractured rock under high-stress and high-water-pressure conditions, revealing the complex interplay between fluid dynamics and fracture propagation in deep fractured rock. The results provide valuable insights into the failure mechanisms and fracture penetration of fractured rock, with potential implications for geological engineering, resource extraction, underground fluid management, and disaster prevention in deep rock environments.

The macro- and meso-mechanical behaviors associated with strain localization in soils were thoroughly investigated using the finite element method (FEM) and the discrete element method (DEM), respectively. First, an elasto-plastic constitutive model based on micropolar theory was developed, highlighting the influence of internal length parameters on the width of the shear band. Additionally, an algorithm was proposed for identifying and calculating the orientation and width of the shear band using the DEM. On this basis, the linear parallel bond model in the PFC (Particle Flow Code) software was used to analyze the effect of particle diameter on the shear bands. The research summarized the potential relationships among particle diameter, internal length scale, element size, and shear band width. It also addressed how the aspect ratio (height-to-width ratio) and boundary conditions of the specimen in the biaxial compression test impact the formation of shear bands. Findings indicated that the shear band width ranged from 6 to 15 times the particle diameter or internal length scale, and that the element size should not exceed five times the internal length scale to ensure mesh-independent results. Different boundary conditions were shown to result in varying shear band modes, including single inclined types, “X” types, or diffuse types. Furthermore, a calibration framework for the meso-parameters was established and validated, providing a crucial link between macro- and meso-material models.

This paper presents an analytical method for solving the problem of shallow rectangular tunnel excavation, explicitly accounting for both the surface slope condition and the soil gravity effect. Firstly, a conformal mapping function for an asymmetric arbitrary cavity is employed to transform the semi-infinite domain containing the rectangular cavity into an annular region in the image plane, simplifying the solution process for the irregular region. Then, utilizing the complex variable method, the fundamental governing equations for the stress and displacement of soil are established, with the stress and displacement boundary condition equations expanded via Fourier series. Subsequently, all the coefficients in the potential function are determined by the boundary condition equations, yielding a complex variable solution for the stress and displacement of soil around the shallow rectangular tunnel under slope condition. Finally, the accuracy of the proposed method is validated through numerical analysis, and the influence of tunnel and soil parameters on the stress and displacement around the tunnel is investigated. The proposed solution can be utilized as a tool to evaluate soil disturbances induced by tunnel excavation during the preliminary design stages.

Accurately describing slurry diffusion in fracture remains challenging due to the complexity of fracture roughness and the non-linear rheological properties of slurry. This study presents an analytical solution for the single-hole grouting in rough fractures considering the time-dependent viscosity of Bingham fluid. Fracture roughness is described by introducing two parameters, the fractal dimension D and the characteristic scale parameter G. The accuracy of the analytical solution is validated by comparing the slurry flow and diffusion radius from experimental results with predicted results. The corresponding slurry flow Q calculated from the analytical solution is used to delineate different areas. Variations in D and G shift the slurry flow resistance from rough (Q < 0.1 L) to transitional (0.1–0.8 L) and smooth (Q > 0.8 L) areas under constant other parameter conditions. Variations in yield stress and viscosity shift the slurry flow areas among low, medium, and high sensitivity areas. Additionally, numerical analysis of two-hole grouting in rough fractures is performed to determine optimal grouting hole spacing based on the percentage of the area covered by the slurry relative to the total fracture area. During two-hole grouting, mutual squeezing effect between slurry alternately promotes and impedes flow. The optimal grouting hole spacing of Bingham fluids with varying water-to-cement ratios decreases with fracture roughness and increases with grouting pressure. Bingham fluids with water-to-cement ratios of 1.0–2.0 exhibit greater sensitivity to grouting pressure in wide fractures due to complex flow characteristics, providing a reference for simplifying grouting process across varying geological conditions.

Tunnel excavation induces stress redistribution and deformation in the surrounding soil, weakening the lateral bearing capacity of adjacent piles and potentially resulting in engineering failures. Therefore, accurately evaluating the mechanism of lateral pile-soil interaction induced by tunnelling is important. This study numerically investigated the pile-soil interaction p_t-y_t curves of a pile adjacent to tunnelling in sand (where p_t denotes the soil force per unit pile length induced by tunnelling and y_t represents the corresponding lateral pile displacement), clarifying the evolution mechanisms of the passive-side (away from the tunnel), the active-side (adjacent to the tunnel), and the resultant p_t-y_t curves, and examining the effects of excavation parameters on the evolution of p_t-y_t curves. The results showed that the evolution of the passive pile p_t-y_t curves can be divided into two stages: the excavation-induced unloading stage and the pile-soil deformation stage. Both the passive-side and active-side p_t-y_t curves evolved synchronously: the passive-side soil force initially increased and subsequently decreased with increasing lateral pile displacement, whereas the active-side soil resistance initially decreased and then increased. Moreover, both the passive-side soil force and active-side soil resistance exhibited opposite trends in response to changes in tunnel diameter, volume loss, tunnelling speed, and the pile-tunnel distance, but exhibited similar trends in response to changes in cover depth and pile diameter.