A DEM numerical model is constructed for analysis of ultimate lateral resistance to piles in sand. The pile was modeled as a rigid body with two kinds of pile movements: rotational and translational movement, simulating free head and fixed head condition, respectively. In the numerical experiments, the lateral resistance, lateral pressure distribution along the pile and the displacement of pile at different depths can be measured and used to construct p-y curve. In addition, the soil-pile interaction can be examined in detail to reveal the extent of influence due to the movement of the pile. In general, the results of the numerical simulation were compared favorably with other semi-empirical solutions.

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Isotropic compression tests were carried out on virtual cemented specimens with different values of cement content and initial void ratio by using three-dimensional (3-D) distinct element method (DEM), and the effect of cementation on cemented sands was examined. First, a simple 3-D bond contact model was introduced to represent the existence of inter-particle cementation. Second, a series of isotropic compression tests were conducted. Finally, the macro and micro-mechanical responses of cemented sands during loading were discussed. The results show that both cement content and density influence the compression curve of the cemented material. The macroscopic yielding is associated with bond breakage on microscopic scale. Bond breakage is primarily due to tension-shear and compression-shear failure, and occurs mainly in the strong contact force network. In addition, the bonded-contact orientation does not vary with compression pressure and cement content.

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This paper presents an extension of a hierarchical multiscale computational method previously developed by the authors to model the behavior of fluid-saturated soils. The original hierarchical multiscale framework is based on rigorous coupling between the finite element method (FEM) and the discrete element method (DEM). It helps to bypass the phenomenological constitutive model in the conventional FEM modeling, and meanwhile faithfully reproduces the typical soil behaviors by DEM simulations at the Gauss points of the FEM mesh which naturally offers great convenience for cross-scale analysis. The current study features a key extension of the framework to further consider the coupled hydro-mechanical behavior in saturated soils based on the u–p formulation. It enables us to take into account the effects of pore fluid pressure and pore fluid flow on the mechanical responses of soil, while retaining reasonable computational efficiency. The approach is first benchmarked by a classic 1D consolidation problem, where the numerical predictions are compared against the closed-form solution. It is further applied to the simulation of a globally undrained biaxial compression test on a dense soil. The interplay between the fluid flow and the strain localization observed in the sample is discussed.

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Soil arching is a unique phenomenon in which soil grains plays an active role in efficiently resisting external load. A traditional trapdoor problem was investigated via a physical model test using bi-dimensional particles made of PTFE elastomer. Each particle was coated by trimmed thin photoelastic sheet such that force transmission can be visualized and their contact forces can be measured. A hierarchical approach for expanding the model size was taken. We attempted the discrete element method (DEM) to simulate existing photoelastic tests, from which microscopic model parameters for DEM were calibrated. The area of the trapdoor problem can easily be enlarged in the discrete element simulations, which overcomes practical limitation in physical model tests. The comparison of the results from the experiment and simulation reveals that the initial condition of the assembly prepared for the DEM is too perfect to reflect the local perturbation in the contact distribution that can be naturally expected in the experiment. Numerically enlarged discrete element models has successfully captured the general patterns of contact force distribution due to the soil arching.

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This paper presents a study on a bonded granular material based on consolidated drained triaxial tests and Distinct Element Method (DEM) analysis. Steel balls of 5 mm in diameter and a metal bonding, i.e. Scotch-weld MC 100, were used to simulate granular material and the bonding between particles. Triaxial consolidation drained tests were conducted on the artificial bonded granular material. The effect of bonding on the mechanical properties is analyzed. The triaxial tests were reproduced with Particle Flow Code (PFC). Comparison of the experimental and numerical results was made. It is indicated that the intergranular cementation has a significant effect on the mechanical properties such as strength, deformation and the bonded granular material exhibits strain softening behavior.

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In order to understand the fundamental behaviour of crushable materials with fines removal in wide stress range, a numerical investigation was conducted. The investigation was carried out using DEM crushable materials because of representation of crushing phenomena. Firstly the volume percentage and microscopic stress of smallest grains regarded as fines were discussed during K0 compression. Then the mechanical behaviour were examined on the void ratio variation and the evolution of particle size of the material during K0 and plane strain compressions after fines removal. The effects of removal was dependent on the stress level. For higher stress level, a reproduction of smaller grains and the corresponding grading change were found out during K0 compression and PSC after the removal. Then the materials indicated same compression and critical state conditions to original material.

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