The macroscopic and mesoscopic study on strengthening mechanisms of the single pile with raft under pile-soil-raft combined interaction

Abstract

Previous studies found that the ultimate bearing capacity of single pile with raft (SPWR) is greater than the sum of the ultimate bearing capacities for single pile and raft foundation. However, the mechanism of this strengthening mechanism is still unclear. This paper studies the bearing capacity characteristics of three different foundation models (i.e., SPWR, single pile and raft foundation) through laboratory tests and discrete element method (DEM) simulations. Specifically, in laboratory tests, the analysis of displacement contour map is conducted to explain the macroscale strengthening mechanism. Subsequently, in DEM simulations, the deformation, force chain and stress transmission of three foundation models are examined, aiming to reveal the mesoscopic strengthening mechanism. The results show that the wedge-shaped elastic core is observed under the raft of SPWR, which is a key element in the strengthening mechanism. On the one hand, the elastic core can strengthen the compactness of soil near the pile side and pile end, which improves the lateral friction resistance and the end bearing capacity of SPWR. On the other hand, the elastic core can increase the range of disturbance to the SPWR, which makes a larger range of soil to bear the load.