结构性黄土一维湿陷特性的离散元数值模拟

针对结构性湿陷性黄土大孔隙和胶结特性，应用离散元生成了不同含水率结构性黄土试样，研究试样的一维湿陷特性。首先，根据已有的结构性黄土试验资料和胶结颗粒材料离散元数值试验成果，建立胶结强度和初始饱和度之间的关系。其次，采用蒋明镜等提出的分层欠压法1]和胶结模型2]制得不同含水率结构性黄土离散元试样，然后进行不同含水率双线法和同一含水率4个压力下单线法湿陷试验的离散元数值模拟。数值模拟结果表明，提出的离散元分析方法能模拟天然结构性湿陷性黄土的主要力学性质，随着含水率的减少，结构屈服应力和最大湿陷压力增加，湿陷系数随着压力先增加后减小，湿陷起始压力为饱和试样的结构屈服应力，单线法湿陷后压缩曲线与饱和试样的压缩曲线接近。此外，模拟结果还表明，不同含水率结构性黄土离散元试样的最大湿陷系数与天然结构性湿陷性黄土相差较远，但在最大湿陷系数与孔隙比的比值上相接近；结构屈服对应着胶结的逐步破坏，湿陷伴随着大量的胶结破坏。提出了基于胶结点数目的损伤变量，研究了其在加载和湿陷过程中的变化规律。研究成果为认识黄土复杂力学特性和建立其本构理论提供了基础。

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.