Investigation of Suffusion Under Torsional Shear Conditions With CFD-DEM

This study investigates, for the first time ever, the suffusion on gap-graded granular soils under torsional shear conditions from a microscopic perspective. A numerical model of the hollow cylinder torsional shear test (HCTST) using the discrete element method (DEM) is first developed, where an algorithm for simulating the real inner and outer rubber membranes of the hollow cylinder apparatus (HCA) is introduced. After the validation, the computational fluid dynamics (CFD) approach is introduced for the coupling between the particle and fluid phases. Then, a series of the coupled CFD-DEM suffusion simulations considering the rotation of the major principal stress axis (α) and intermediate principal stress ratio (b) are conducted. It is found that more fine particles are eroded in cases having smaller α and b, and the clogging phenomenon in the middle zones becomes more significant as both α and b increase. From the microscopic perspective, the specimens whose contact anisotropy principal direction is close to the fluid direction will lose more fines, and the anisotropy magnitude also plays an important role. In addition, the differences in structure and vertical connectivity of the pores in HCTST samples under various complex loading conditions cause fine particles to have different migration paths, further resulting in different fines mass loss.