CFD-DEM modelling of suffusion in multi-layer soils with different fines contents and impermeable zones

Abstract

目的 不同细颗粒含量及含不透水区域层状土中的潜蚀过程与均质土中的潜蚀过程存在差异。本文旨在探讨非均质土以及复杂边界条件下间断级配土的潜蚀过程。 创新点 1. 建立计算流体动力学-离散元法(CFD-DEM)耦合数值模型, 并通过单颗粒下落速度和Ergun测试进行模型验证, 确认该方法的准确性; 2. 分析不同细颗粒含量层状土对潜蚀量的影响, 从而阐述非均质土中潜蚀的演化过程; 3. 揭示层状土中不同分布的不透水区域对潜蚀的影响。 方法 1. 采用颗粒下落以及Ergun测试对CFD-DEM耦合数值模拟中流体及颗粒参数进行标定(图2); 2. 利用标定参数对具有不同细颗粒含量的层状土试样进行潜蚀模拟(图7); 3. 对含有不透水区域的层状土试样进行潜蚀模拟。 结论 1. 对于层状土样, 累积侵蚀质量主要由底层土层决定; 一般来说, 底层土层的细颗粒含量越多, 累积侵蚀量越大; 此外, 当底层以上的土层细颗粒含量较高时, 潜蚀得到缓解; 反之, 则潜蚀较为严重。2. 对具有不同不透水区域的试样进行的测试表明, 流量在决定累积质量方面起主要作用; 土样内部的不透水区域可以增加周围区域的流速, 有利于细颗粒的迁移, 加剧潜蚀; 但当不透水区域较多时, 由于增加了流动路径的长度, 阻碍细颗粒的迁移, 潜蚀程度则有所降低。 Suffusion in broadly graded granular soils is caused by fluid flow and is a typical cause of geo-hazards. Previous studies of it have mainly focused on suffusion in homogeneous soil specimens. In this study, the coupled discrete element method (DEM) and computational fluid dynamics (CFD) approach is adopted to model suffusion in multi-layered soils with different fines contents, and soils with one or more impermeable zones. The parameters of the CFD-DEM model are first calibrated with the classic Ergun test and a good match with experiment is obtained. Then suffusion in multi-layered soils with different fines contents and impermeable zones is simulated and discussed. The simulation results show that, for soils with multiple layers, the cumulative eroded mass is mainly determined by the fines content of the bottom layer. In general, the higher the fines content of the bottom soil layer, the higher the cumulative eroded mass. In addition, suffusion is more severe if the fines content of the layer above is decreased. Impermeable zones inside soil specimens can increase the flow velocity around those zones, facilitating the migration of fine particles and intensifying suffusion.