Study on Failure Mechanism of Cushion in Rigid Pile Composite Foundation

In order to study the failure mechanism of interaction between cushion and rigid pile,model tests on rigid pile composite foundation were carried out in a tempered glass box.The digital photogrammetry was used to investigate the deformation field of soil particles in cushion at the top of pile.The displacement field of soil particles in cushion was observed and analyzed globally during the loading procedure.Particle flow code of two-dimensional discrete element method was developed to simulate the failure mechanism of cushion in rigid pile composite foundation.Numerical analysis results were compared with the experimental results.The failure mode of the cushion soil was put forward,according to the results of model test and numerical simulation.Based on plastic equilibrium theory,a formula to solve the stress of pile top,soil between piles and pile-soil stress ratio was derived when the cushion failed.The theoretical results calculated by the formula were compared with the test data.The results show that thetheoretical calculation results of the stress of pile top agree well with the test data,which can meet the engineering requirement of accuracy.The establishment of cushion failure mode is helpful to reveal the bearing mechanism of cushion in rigid pile composite foundation.