Abstract: In this paper,an effective numerical method for physically nonlinear interation analysis is studied,in which the elasto-plastic problem of coupled analysis between the structure and medium may be transformed into several linear problems by means of the perturbation technique,then the finite strip method and finite layer method are used to analyse the underground structure and rock respectively,for their corresponding linear problems,so the purpose of simplifing the calculation can be achieved.This kind of method has made use of the twice semi-analytical technique.the perturbation and semi-analytic solution function to simplify 3-D nonlinear coupled problem into 1-D linear numerical one.In addition,this method is a new advance of semi-analytical method in the application to nonlinear problems by means of combinating with the analytical perturbation method,and it is also a branch of the perturbational numerical,nethod developed in last years.

Key words: perturbation, semi-analytic method, elasto-plasticity, coupling