Wetting-Induced Collapse Behavior of Unsaturated and Structural Loess under Biaxial Tests Using Distinct Element Method

Abstract

Loess soils undergo collapse when the material is loaded and wetted, which leads to engineering problems and disasters. To understand better the collapse mechanisms that govern loess and loess-like deposits under complex stress paths, a distinct element model has been established. A contact model considering water content effect introduced for structural loess was used to cement contacted particles together to simulate unsaturated structural loess under biaxial compression conditions. The numerical structural loess was tested for different wetting and loading paths, i.e., loading-quick wetting (LWQ), loading-gradual wetting (LWG), and wetting-loading (WL) paths. The simulated macroscopic mechanical behavior agrees approximately quantitatively in terms of the deviatoric deformation and qualitatively regarding the volumetric deformation when compared with available experimental results. The tests under different mean stresses indicate the existence of initial, maximum, and terminating collapse stress states in a biaxial wetting test. The influence of the wetting procedure, i.e., gradual wetting or quick wetting, has a considerable effect on the mechanical performance for numerical samples. The axial strain of a sample during a loading-wetting (LW) path is larger than that of a sample in a WL path. The wetting-induced volumetric deformation corresponds with the failure of bonded contacts. The deviator fabrics (fabric anisotropy) of total, bonded, frictional, and broken bond contacts were also investigated.