Three-dimensional numerical modelling of progressive failure of caisson foundation in sand using a coupled FDM–DEM method

Bearing capacity and the relationship between loading and displacement for caisson foundations have been widely studied, but failure mechanism and loading response at the micro level were out of their reach. Considering the pros and cons of both discrete and continuum methods, this study investigates the progressive failure of caisson foundation in sand using the coupled FDM–DEM (Finite Difference Method – Discrete Element Method) method. The caisson is modelled by shell elements of FDM and its surrounding soils in a limited area are modelled by spherical particles of DEM with the rest part of soil modelled by FDM. Rolling resistance contact model is used to account for the effect of particle shape of sand. A series of scale model tests are simulated for investigating the failure process of the caisson foundation in sand under various combined horizontal force and moment loadings. Based on simulations, the macro and micro characteristics of surrounding soils of caisson are analysed during the failure process of the foundation. In particular, soil displacement, rotation, force chain and fabric anisotropy in failure zone are analysed at particle level to explain macro responses, which improves the understanding of the micro-mechanisms in the progressive failure process of caisson foundation.