A nonlinear elasto-perfect plastic model of interface element is presented. The proposed model can simulate behavior of soil and structure interaction. The stress-strain relationship and nonlinear elasto-perfect plastic matrix of interface element are established based on elastoplasticity theory. The computational procedure for implementing this-type of nonlinear and inelastic interface element in the finite element methods is developed and numerical scheme is presented. Then the method is applied to numerical analyses of foundation pit excavation. Through numerical computations for an example of the foundation pit excavation and bracing

the distributions of earth pressures behind and in the front of pile wall along the depth and their variations during the excavation of foundation pit are examined. It is indicated that the proposed model can rationally simulate the stress-strain relationship of interface element and will be practically applicable.