Discrete element method based investigation on displacement and bearing characteristics of pile foundation under seepage erosion

With the increasing complexity of the three-dimensional cross-distribution system of pile foundations and tunnels in the urban underground space, the stability of the pile foundation caused by tunnel seepage erosion becomes more and more prominent. However, the current research mainly focuses on the mechanism of erosion induced by defective tunnels, and little on its interaction with the adjacent pile foundation. Thereby, based on the seepage erosion mechanism revealed by the physical model test, the erosion-induced stratum form is quantitatively characterized by establishing the critical fine particle content expression. Subsequently, a multi-zone eroded strata model is simulated by the random and quantitative removal of fine particles in the DEM domain, and then the erosion response characteristics of the foundation under different positions, loads, sinking methods and types are analyzed. The results show that the pile foundation has different degrees of subsidence under different erosion conditions, and tilts to the eroded area under the drive of unbalance force on its eroded position. After the erosion-induced reduction, the pile-tip resistance increases gradually with the subsidence, but the loss of lateral frictional resistance is basically unrecoverable. In addition, the changing mode of displacement and resistance of the pile is basically the same under different sinking methods and loads, only different in the changed amount. Compared with the single pile, pile group foundation has a better erosion resistance.