Microscopic modeling of particle suffusion in dam filter layers using CFD-DEM

The filter layer is a crucial component in preventing internal erosion in earth-rockfill dams. Its design typically replies on the particle size distribution of the filter material and base soil, with the ratio between them (i.e., interlayer coefficient) playing a critical role in controlling the blockage and interception process of eroding particles. To better understand how the interlayer coefficients affect subsoil erosion and the retention capacity of filter material, we simulate a reverse filtration system under varying interlayer coefficients using a novel 3D coupled computational fluid dynamics-discrete element method (CFD-DEM) that incorporates irregularly shaped particles. The numerical results indicate that: (1) A smaller interlayer coefficient more effectively inhibits base soil erosion, with the erosion process progressing through three stages: rapid erosion, slow erosion, and stability; (2) The interlayer coefficient significantly influences the transport behavior of soil particles. Interlayer coefficients above 6 weaken the retention capacity of the filter material, causing noticeable subsurface suffusion and damage to the base soil. In contrast, Coefficients below 4 result in the accumulation of fine soil particles at the interface, forming a weakly permeable layer resembling a “filter cake”. A new filter layer design criterion is proposed based on the numerical tests above and is validated through experimental results from the literature. This study provides valuable insights into the microscopic characteristics and suffusion mechanisms of the base soil-filter system, offering practical guidance for the design of filtration systems.