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

The contraction or expansion of a cylindrical cavity in an elastoplastic medium is usually analyzed from a continuum based approach with a plasticity constitutive model. However, localized deformations, which are rooted in the post-failure softening response of geomaterials, are observed in the form of spiral-shaped fractures in laboratory tests. An alternative approach based on dislocation theory is introduced in this paper for modeling cavity contraction or expansion. In this model, several equally spaced spiral-shaped shear fractures initiate and propagate away from the cavity within the linearly elastic medium. The Mohr-Coulomb criterion and a dilatancy rule are imposed on the shear fractures to constrain the stresses and the displacement jumps. The direction of fracture propagation is determined by minimizing plastic dissipation. The displacement discontinuity method is used to discretize the shear and normal displacement jumps along the fracture and solve the problem numerically. The calculated crack path follows a logarithmic-like spiral, similar to the slip lines predicted by plasticity theory. The relationship between the pressure and radial displacement at the cavity boundary converge towards the classical elastoplastic solution as the number of fracture branches increases.

Loose granular materials may also exhibit instability behaviors similar to liquefaction under drained conditions, commonly referred to as diffuse instability, which can be studied through constant shear drained (CSD) tests. So far, the research on CSD in binary mixtures is still insufficient. Therefore, a series of numerical tests using the discrete element method (DEM) were conducted on binary mixtures under CSD path. The possible model of instability is categorized into type I and type II, type I instability occurs prior to reaching the critical state line (CSL), whereas type II instability occurs after exceeding the CSL. The study analyzes the macroscopic instability behavior and the impact of fine content (FC) on macroscopic instability behavior. The numerical results show that as FC increases, the slope of the instability line (IL) increases initially and then falls in the p-q plane. In the e-p plane, the IL decreases initially and then ascends. The instability type of the binary mixtures is influenced not only by relative density but also by FC. The stability index increased first and then decreased with the increase of FC. The microscopic origin of binary mixtures instability is explored by investigating the fabric-stress relationship. The collapse of the weak contact sub-network triggers the specimen instability, while the strong contact sub-network dictates the difficulty of achieving instability. FC influences the evolution of fabric anisotropy of the strong and weak contact networks, thereby controlling the macroscopic instability behavior of binary mixtures.

Fully grouted rock bolts are widely used in mining, tunneling, and pit support, and thus the study of their anchorage performance is beneficial for optimizing the anchorage system design. In this study, an FDM-DEM coupled numerical model is established to simulate the whole process of rock bolt pullout test and to investigate the failure mechanism of fully grouted rock bolts. The accuracy of the model is verified by comparison with existing laboratory test results. Virtual experiments are conducted on different models by eliminating the anchor plate, changing the layered rock strata condition, and adding bolts. The results show that the presence of an anchor plate will reduce tensile stress to restrain the rupture of surrounding rock and thus improve the strengthening effect. Due to the different bond strength and tensile strength of the soft and hard rock mediums, the layer sequence of the rock strata affects the maximum pullout force. The upper-soft and lower-hard composite rock strata (S-HCR) exhibits single-cone damage while the upper-hard and lower-soft composite rock strata (H-SCR) exhibits double-cone damage. The superposition effect of the anchor group on the stresses and displacements is the reason leading to the reduction of the maximum load-bearing capacity of the rock bolts.

This study establishes a theoretical framework for analyzing the lateral oscillation of marine pipe piles. The additional mass model is introduced herein to consider the inertial fluctuation effect of the soil plug. Analytical mathematical methods are used to determine the complex impedance variation of the pile over a range of frequency effects. An investigation is performed to determine how the presence of soil plugs changes the lateral complex stiffness and natural frequency of pipe piles. Additionally, comparisons of the applicability of the plane strain model and continuous medium model have been conducted to enable the easy use of the theoretical model. The main conclusions can be drawn as (1) if the fluctuation inertia effect of the soil plug is not taken into consideration, the dynamic active length and the dynamic stiffness of the pipe pile will be underestimated; (2) for the soft soil, the plane strain model may give rise to substantial calculation errors attributed to them regardless of the vertical continuity of the soil, nevertheless, the calculation error decreases rapidly with the increase of soil shear modulus and vibration frequency.

The shapes and morphological features of grains in sand assemblies have far-reaching implications in many engineering applications, such as geotechnical engineering, computer animations, petroleum engineering, and concentrated solar power. Yet, our understanding of the influence of grain geometries on macroscopic response is often only qualitative, due to the limited availability of high-quality 3D grain geometry data. In this paper, we introduce a denoising diffusion algorithm that uses a set of point clouds collected from the surface of individual sand grains to generate grains in the latent space. By employing a point cloud autoencoder, the three-dimensional point cloud structures of sand grains are first encoded into a lower-dimensional latent space. A generative denoising diffusion probabilistic model is trained to produce synthetic sand that maximizes the log-likelihood of the generated samples belonging to the original data distribution measured by a Kullback-Leibler divergence. Numerical experiments suggest that the proposed method is capable of generating realistic grains with morphology, shapes and sizes consistent with the training data inferred from an F50 sand database. We then use a rigid contact dynamic simulator to pour the synthetic sand in a confined volume to form granular assemblies in a static equilibrium state with targeted distribution properties. To ensure third-party validation, 50,000 synthetic sand grains and the 1542 real synchrotron microcomputed tomography (SMT) scans of the F50 sand, as well as the granular assemblies composed of synthetic sand grains are made available in an open-source repository.

The cover image is based on the article Competition among simultaneously stimulated multiple hydraulic fractures: Insights from DEM simulation with the consideration of fluid partitioning by Xuejian Li et al., https://doi.org/10.1002/nag.3801.

The current study presents superposition-based concurrent multiscale approaches for porodynamics, capable of capturing related physical phenomena, such as soil liquefaction and dynamic hydraulic fracture branching, across different spatial length scales. Two scenarios are considered: superposition of finite element discretizations with varying mesh densities, and superposition of peridynamics (PD) and finite element method (FEM) to handle discontinuities like strain localization and cracks. The approach decomposes the acceleration and the rate of change in pore water pressure into subdomain solutions approximated by different models, allowing high-fidelity models to be used locally in regions of interest, such as crack tips or shear bands, without neglecting the far-field influence represented by low-fidelity models. The coupled stiffness, mass, compressibility, permeability, and damping matrices were derived based on the superposition-based current multiscale framework. The proposed FEM-FEM porodynamic coupling approach was validated against analytical or numerical solutions for one- and two-dimensional dynamic consolidation problems. The PD-FEM porodynamic coupling model was applied to scenarios like soil liquefaction-induced shear strain accumulation near a low-permeability interlayer in a layered deposit and dynamic hydraulic fracturing branching. It has been shown that the coupled porodynamic model offers modeling flexibility and efficiency by taking advantage of FEM in modeling complex domains and the PD ability to resolve discontinuities.

The complexity and variability of the structural distribution and combination characteristics of jointed rock masses make the response mechanism of tunnel rock collapse different, and there is a lack of systematic research on the existing perimeter rock instability mode and bolt support scheme. Based on numerical simulations of the block system structure of a nodular rock mass, the existing theory of bolt support is compared and analyzed to explore the scope of their respective applications. Combined with the spatial and temporal transport law of block instability, a new batch instability model of jointed rock tunnels is proposed, which reveals the progressive collapse catastrophe evolution mechanism of a collapsed interlocking block system after the instability of the key blocks and elucidates the coupling mechanism between the bolts and the block system structure as well as their anchoring effectiveness. Finally, for the actual tunnel project, the instability batches of the surrounding rock are identified, and the corresponding optimized design of the bolt support is presented, which has achieved good support effects. The research results can provide important theoretical guidance and practical engineering value for risk avoidance, disaster identification and targeted prevention and control of dangerous rock fall and chain collapse instability disasters in jointed rock body tunnels.

Slow and very slow landslides can cause severe economic damage to structures. Due to their velocity of propagation, it is possible to take action such as programmed maintenance or evacuation of affected zones. Modeling is an important tool that allows scientists, engineers, and geologists to better understand their causes and predict their propagation. There are many available models of different complexities which can be used for this purpose, ranging from very simple infinite landslide models which can be implemented in spreadsheets to fully coupled 3D models. This approach is expensive because of the time span in which the problems are studied (sometimes years), simpler methods such as depth-integrated models could provide a good compromise between accuracy and cost. However, there, the time step limitation due to CFL condition (which states that the time step has to be slower than the ratio between the node spacing $��\Delta �x�$ and the physical velocity of the waves results in time increments which are of the order of one-10th of a second on many occasions. This paper extends a technique that has been used in the past to glacier evolution problems using finite differences or elements to SPH depth-integrated models for landslide propagation. The approach is based on assuming that (i) the flow is shallow, (ii) the rheological behavior determining the velocity of propagation is viscoplastic, and (iii) accelerations can be neglected. In this case, the model changes from hyperbolic to parabolic, with a time increment much larger than that of classic hyperbolic formulations.

This paper presents an analytical solution for combined vertical and torsional shear loading of a cylindrical cavity in undrained modified Cam-Clay. The governing partial differential equations for the cylindrical cavity are established in the polar coordinate. The problem is formulated as a set of first-order differential equations by using the axisymmetric condition, equilibrium equations, and elastic-plastic constitutive relationship. The influence of the second shear loading on the initial shear strain is considered in the plastic state. Then the stress-strain distributions can be calculated by integrating within the elastic and plastic zones around the cavity. A finite element method simulation of the cavity under combined shear loading is established to verify the proposed approach, and the results are in good agreement with the proposed analytical solution. Parametric analyses are carried out on the effects of clay overconsolidation ratios and in situ stress coefficients under different loading paths and loading ratios. The results show that the combined shear loading on the cavity wall has a significant effect on the stress distribution of the surrounding soil, and the influence of the loading path cannot be neglected.