Microscopic Mechanism of Horizontal Force Transmission of a Cushion in a Rigid Pile Composite Foundation

ABSTRACT The horizontal force transmission mechanism of a cushion in a composite foundation is crucial in engineering practice, but has not been investigated systematically. An interface shear test and coupled discrete element method–finite difference method (DEM–FDM) were used to establish a rigid pile composite foundation model. The microscopic response of the cushion was analyzed by discrete element modeling to understand the microscopic force transmission mechanism of the cushion during the horizontal loading of the rigid pile composite foundation. The results showed that the stress field, coordination number field, and contact force chain reflected the internal force of the cushion under a horizontal load. The cushion layer exhibited a stress concentration as the horizontal load increased. The direction of the principal stress was deflected, and the direction of the force transmission changed from the vertical direction at the end of vertical loading to the direction of 45° due to the shearing action. The number of particle contacts in the area of the major principal stress increased, forming stronger contact force chains, and the coordination number of the soil particles increased.