Perturbation analysis of nonlinear settlement for pile group in multilayer soils

A continuous version of St. Venant model, named continuous Masing-Iwan model which includes an internal variable, is adopted to simulate the nonlinear behaviors of soils in confined disturbed zone around pile-soil interface. Based on this model two different nonlinear load transfer functions are developed for single piles. By adopting the assumption that the pile-soil-pile interaction effect is elastic and the principle of superposition, two new kinds of load transfer models are obtained for piles in group. Furthermore, by comparing with elastic governing equation, a procedure of perturbation analysis is developed to solve the nonlinear governing equation for both single pile and piles in pile group in an approximate analytical way. The theoretical solution can be asymptotic to the elastic solution rigorously under lower loading and reflects the nonlinearity of load-displacement distribution up to the failure. Finally, the predictions of load settlement distribution from the proposed method are compared with a well-documented full scale field pile group test data, which shows the effectiveness and applicability of these proposed methods.