Influence mechanism of particle friction characteristics on seepage-induced erosion behavior of gap-graded granular systems based on CFD–DEM simulation

To investigate the influence of interparticle friction on the seepage erosion process, a numerical model of seepage erosion in a gap-graded granular system was established using a coupled computational fluid dynamics and discrete element method (CFD–DEM). The macroscopic and microscopic responses of seepage erosion under different interparticle friction conditions were investigated, including fine-particle mass loss, particle migration characteristics, and the evolution of contact force chains. The results show that increasing the hydraulic gradient accelerates fine-particle migration and intensifies internal erosion, while also making the influence of interparticle friction on the erosion process more pronounced. Lower interparticle friction facilitates particle rolling, sliding, and detachment, thereby promoting fine-particle migration and accelerating the erosion process. In contrast, higher interparticle friction enhances the mechanical constraints between particles and promotes the formation of strong contact force chain networks, thereby inhibiting fine-particle migration and the development of preferential seepage channels. At intermediate friction coefficients, the migration behavior of fine particles becomes more complex and less predictable.