This study presents a hierarchical multiscale approach that combines the finite-element method (FEM) and the discrete-element method (DEM) to investigate tunneling-induced ground responses in coarse-grained soils. The approach considers both particle-scale physical characteristics and engineering-scale boundary value problems (BVPs) simultaneously, accurately reproducing typical tunneling-induced mechanical responses in coarsegrained soils, including soil arching and ground movement characteristics observed in laboratory tests and engineering practice. The study also unveils particle-scale mechanisms responsible for the evolution of soil arching through the underlying DEM-based RVEs. The results show that the rearrangement of microstructures and the deflection of strong contact force chains drive the rotation of macroscopic principal stress and the formation of soil arch. The microscopic fabric anisotropy direction can serve as a quantitative indicator for characterizing soil arching zones. Moreover, the effects of particle size distributions (PSD) and soil densities on ground deformation patterns are interpreted based on the stress-strain responses and contact network characteristics of DEM RVEs. These multiscale insights enrich the knowledge of tunneling-induced ground responses and the same approach can be applied to other geotechnical engineering analyses in coarse-grained soils.

The stress state and density of soil have been considered as the key factors to determine the liquefaction resistance. However, the results of seismic liquefaction case histories, laboratory tests and centrifuge model tests show that the fabric characteristics also influence liquefaction resistance, even more significantly than the contributions of stress state and density. In this study, anisotropic specimens with different consolidation histories were prepared using the 3D Discrete Element Method (DEM) to investigate the influence of fabric characteristics on the mechanical behavior of granular materials and the underlying mechanisms. The simulations revealed that under monotonic shear conditions, horizontally anisotropic specimens exhibited strain hardening and dilatancy characteristics, as well as higher peak strength. Under cyclic shear condition, the normalized liquefaction resistance of the specimens showed a strong linear relationship with the degree of anisotropy, independent of confining pressures and density. Microscopic results indicate that the fabric arrangement aligned with the loading direction leads to the evolution of the mechanical coordination number and average contact force in a manner favorable to resisting loads, which is the underlying mechanism influencing macroscopic mechanical properties. Additionally, the evolution patterns of contact normal magnitude and angle in anisotropic granular materials under cyclic loading conditions were also analyzed. The results of this study provided a new perspective on the macroscopic mechanical properties and the evolution of the microstructure of granular soils under anisotropic conditions.

The existing lunar exploration activities and associated equipment interactions are limited to the surface environment, where the stress state of the lunar regolith is significantly lower than that in laboratory tests conducted on Earth. To address this, this paper proposes a new framework for discrete modeling of large-scale triaxial tests on lunar regolith under low confining pressure. The framework incorporates particle shapes from the Chang'E-5 mission (CE-5) and flexible boundary conditions. Firstly, the shape characteristics of the lunar regolith particles were adopted in the Discrete Element Method (DEM) model to reproduce the mechanical properties of the lunar regolith as accurately as possible. Then, experiments with varying membrane particle stiffness ratios were conducted to explore the effect of the rubber membrane's properties on the mechanical characteristics of lunar regolith under low effective confining pressure. Topological Data Analysis (TDA) tools from persistent homology were utilized to quantify the dynamic response of particles during the onset and development of strain localization. The results indicate that under low effective confining pressure, selecting appropriate rubber membrane types is crucial for accurately determining the mechanical properties of lunar regolith. (c) 2024 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The soils in situ are subjected to various types of preloading histories. Extensive work has been devoted to understanding the impact of undrained preloading with different strain histories on the reliquefaction resistance of sands. This study primarily examines the effects of drained cyclic preloading histories on the liquefaction resistance of soils using DEM-clump modeling. The effects of preloading stress path and preloading deviatoric stress amplitude on the drained cyclic behavior and subsequent undrained liquefaction response are discussed. Moreover, the evolution of two microscale descriptors, including coordination number Z and fabric anisotropy degree ac, during the total process is analyzed. The results demonstrate that a smaller preloading stress amplitude and an increasing preloading cycle generally increase the liquefaction resistance of sandy soils. In comparison, a larger preloading stress amplitude significantly reduces the liquefaction resistance. We also reveal that drained cyclic preloading histories induce soil samples with different relative densities and fabrics. The relationship between relative density and liquefaction resistance of soils is not unique. Essentially, Z and ac are good indexes for determining the liquefaction resistance of soils with various drained cyclic preloading histories. The primary objective of this study is to elucidate the micromechanical effects of drained cyclic preloading on the liquefaction resistance of sandy soils.