Micromechanical analysis of local scour behaviors around circular piles in granular soil under steady flows with SPH-DEM

The micro-mechanism of local scour around circular piles in granular soil under steady flows remains unclear. This study investigates local scour around circular piles with the coupled Smoothed Particle Hydrodynamics-Discrete Element Method (SPH-DEM) for the first time, taking the effects of scour lengths and flow velocities into consideration. The granular soil and piles are modeled using DEM elements, while the water is modeled using SPH elements. The flow regularity and scour holes in numerical simulations are compared with those in experiments, while detailed pile-water-soil interactions are analyzed. The findings demonstrate that the flow behaviors evolve with the development of scour holes. Large deformation and turbulent flow occurrences surrounding piles are successfully simulated using the SPH-DEM approach and their relationships to scour lengths are discovered. Besides, relationships between local flow direction, vortexes, and soil erosion are established by analyzing the streamlines and fluid force on particles. Furthermore, detailed investigations of particle transportation and scour holes under both flow and flow-stop conditions lead to an identification of conclusive modes of soil erosion around piles. This study provides novel insights into local scour behaviors around pile foundations in granular soil. • Local scour around piles is analyzed using the SPH-DEM approach for the first time with the micromechanics insight. • The evolution of turbulent regions and soil erosion is captured from macro to micro scales. • Large deformations and turbulent flows are effectively simulated. • Mechanisms of local scour holes under both flow and flow-stop conditions are discovered.