Abstract:The stresses and deformations of soils and support structures of foundation pit will change continuously during the course of excavation and supporting. The physical non-linearity of soils and the contact non-linearity of interface between soils and support structures often form the double nonlinear question of civil engineering structures. The mechanical characteristics of foundation engineering are represented based on the detailed description of support system. Then the finite element method and the nonlinear iterative method are presented considering the process of excavation and supporting and the double non-linearity problem. Finally,an illustrative example is analyzed numerically,the relationship between the distribution mode of tension stresses of soil nailing and shear stresses of nailing-soil interface,and the excavation steps are studied. Computational results show that the presented method is rational.