结构性黄土压缩特性的微观非连续变形分析

Microscopic Discontinuous Deformation of Structured Loess under Compression

黄土的结构性与其形成过程密切相关,并对其物理力学性质产生重要影响。针对结构性黄土的大孔隙和胶结特性,对DDA算法进行了扩展,将结构性黄土中起主要胶结作用的黏粒胶结嵌入已有的DDA算法中;使用Monte Carlo法和DDA模拟黄土的沉积过程,该方法能够模拟颗粒下落过程中的相互碰撞及摩擦,分析结构性黄土在压缩过程中颗粒的平动和转动规律,由此构建与原状黄土孔隙比接近的微观结构模型;进一步使用扩展DDA对所生成的黄土结构模型进行不同压力下的一维压缩试验模拟,并与室内压缩试验进行对比。发现胶结试样颗粒位移比不含胶结试样颗粒位移小,但整体规律相似;每个颗粒位移的大小和方向不尽相同,但主要以竖向位移为主;在压缩过程中,不同区域的颗粒位移存在较大差异,上部颗粒位移大,越往下部颗粒的位移越小。该研究成果可为从微观认识黄土力学行为提供一条途径。

The structure of loess is closely related to its formation process and has an important impact on its physical and mechanical properties.In view of the large pores and cementation features of structured loess,we embedded the clay cementation which plays a major role in structured loess into the existing DDA.By using Monte Carlo method and DDA,we simulated the deposition process of loess,in particular,the collision and friction of particles in the falling process and analyzed the translational and rotational movements of particles in the consolidation process.On this basis,we constructed a microstructural loess model which is close to undisturbed loess in terms of void ratio.Furthermore,we simulated one-dimensional compression test on the structured loess model under different pressures with the extended DDA,and compared with indoor compression test to demonstrate the reliability of the numerical simulation.We found that,despite similar overall trends,the particle displacement of cemented sample was smaller than that of non-cemented sample.Vertical displacement of particles dominated regardless of some differences in the degree and direction of displacements.Major differences existed in different parts,i.e.,upper particles underwent larger displacement,while lower particles witnessed smaller displacement.