Simulation of collapsible characteristics of structural loess under one-dimensional compression condition by discrete element method

Focusing on large voids and bonds of natural loess, structural loess samples with different water contents are prepared by discrete element method (DEM) and their collapsible characteristics under one-dimensional compression condition are investigated. First, based on laboratory test results on natural loess and DEM numerical results on bonded granular materials, the relation between bond strength and initial saturation is proposed. Then structural loess samples with different water contents are prepared by using the authors' multilayer under-compaction method and bonded contact model. Then double-oedometer tests on these samples with different water contents, single-oedometer tests on samples with same specific water content are simulated by DEM. The DEM results show that the structural yield stresses and the vertical pressures at maximum coefficient of collapsibility increase with decreasing of water content. The coefficient of collapsibility increases firstly and then decrease with pressure. The initial collapse pressure is equal to structural yield stress of saturated samples. The ratio of maximum coefficient of collapsibility to void ratio is near to that of natural collapsible loess. There is a nearly unique post-collapse compression line for DEM samples wetted at different vertical pressures. The yielding is related to bonds breakage and the collapse is accompanied with significant bonds breakage. Structural damage variable based on the bond number is proposed to reflect the damage degree of structure and its evolution during loading or wetting is studied. This study provides a foundation for learning the complex mechanical characteristics of loess and building constitutive law of loess.