DEM-DFM modeling of suffusion in calcareous sands considering the effect of double-porosity

Calcareous sand is a kind of marine biogenic sand formed by coral debris and marine organism skeletal bodies. One of the most important features of calcareous sand lies in remarkable void space within the particles (intra-particle voids), which, combined with the voids among particles, produces the double-porosity structure. The double-porosity structure enables both inter-particle and intra-particle flows in calcareous sand during a seepage process, which influences the migration of fine particles. This study presents a numerical investigation of internal erosion in calcareous sand with the double-porosity structure by considering both inter-particle and intra-particle flows. A gap-graded sand specimen is generated using the discrete element method (DEM), in which the coarse particles are assumed as calcareous sand and contain internal porosity. The dynamic fluid mesh (DFM) is improved with a double-porosity algorithm to consider both inter-particle and intra-particle flows. The solid --fluid interaction is simulated by coupling DEM and DFM. With this method, seepage erosion in calcareous sand is simulated, and the effect of double-porosity is revealed. Results show that the intra-particle porosity increases flow velocity and thus increases the percentage of erosion mass and the flow velocity. In addition, the intra-particle flow velocity is not affected by the fines content.