A simplified analytical method is presented for nonlinear analysis of the behaviour of pile groups under vertical loads. A hyperbolic approach is adopted to describe the nonlinear relationship between the shaft shear stresses and the relative shaft displacements along a confined disturbed soil zone around a pile-soil interface. Outside the disturbed zone, the soils are assumed to behave in a linearly elastic state. By adopting the elastic closed-form analytical solution to approximate the displacement fields around a single vertically loaded pile, and the principle of superposition, a new transfer function is presented for analysis of the behaviour of pile groups in multilayered soils. Furthermore, with a simplified assumption of separating the shaft from the base interaction factors for individual piles in a pile group, a highly effective iterative procedure is developed to examine the nonlinear loaddisplacement behaviour of a pile group up to the failure state. Comparisons of the loadsettlement responses for a number of well-instrumented field pile group test results are given to demonstrate the effectiveness and accuracy of the proposed analytical method. The computed nonlinear responses of the pile group compare favourably with measured field test results under both rigid and flexible pile cap conditions.Key words: pile groups, interface, transfer function, settlement analysis, nonlinear behaviour.
