循环荷载作用下土体接触侵蚀的CFD-DEM耦合模拟

Micro-mechanism of contact erosion between soil layers under cyclic loading based on CFD-DEM coupling

关键词:  土体接触侵蚀  CFD-DEM耦合  颗粒迁移  宏观变形  细观机理

Key words:  contact erosion  CFD-DEM coupling  particle migration  macroscopic deformation  mesoscopic mechanism

摘要:

为研究循环荷载作用下土体层间中常见的渗流侵蚀特性,揭示水-力耦合作用下的接触侵蚀的细观机理,考虑循环荷载幅值的影响,建立了一种基于计算流体动力学(CFD)与离散单元法(DEM)耦合的土体接触侵蚀三维计算模型。首先,分析了不同循环荷载作用周次内的颗粒运动规律与空间分布特征。其次,探讨了由于颗粒侵蚀引起的宏观变形响应特性。同时,选取两个局部变形区域,研究了两种典型的颗粒迁移模式。最后,结合力链分析,讨论了侵蚀过程中的颗粒接触力学演化机制。研究结果表明:在一次循环荷载作用的过程中,加载导致的粗颗粒层挤压与卸载产生的应力松弛均是导致细颗粒发生迁移的主要因素；循环荷载作用会使得土层接触面处产生剧烈的颗粒迁移运动,进而导致试样产生较大的轴向变形,同时渗流场会产生向上的水力梯度以促进细颗粒发生泵送迁移。存在一个幅值阈值,当循环荷载幅值超过该阈值后,土体迅速密实,引起侵蚀变形减弱。

Abstract:

To investigate the seepage erosion characteristics commonly found between soil layers under cyclic loading and to reveal the micromechanical mechanisms of contact erosion under water-flow coupling, a three-dimensional computational model for soil contact erosion was developed, based on the coupling of computational fluid dynamics (CFD) and discrete element method (DEM), considering the influence of cyclic loading amplitude. Firstly, the movement patterns and spatial distribution characteristics of the particles were analyzed within different cyclic loading periods. Secondly, the macroscopic deformation characteristics resulting from particle erosion were explored. At the same time, two localized deformation regions were selected to study two typical particle migration modes. Finally, the evolution mechanism of particle contact mechanics during the erosion process was discussed, combined with force chain analysis. The results show that during a single cycle of loading, the compression of coarse particles caused by loading and the stress relaxation induced by unloading are the primary factors responsible for the migration of fine particles. Cyclic loading induces intense particle migration at the soil layer interface, resulting in significant axial deformation of the sample. Simultaneously, the seepage field generates an upward hydraulic gradient that promotes the pump-driven migration of fine particles. A threshold value for the loading amplitude exists, and the soil rapidly compacts when the cyclic loading amplitude exceeds this threshold, leading to a reduction in erosion-induced deformation.