Performance prediction of axially loaded piles and pile groups by load transfer method

Abstract

Nowadays, economic and population growth around the world increase the speed of urbanization, making skyscrapers become popular. Together with the development of high-rise buildings, the requirements of capacity and settlement of foundations become complex and demanding. In particular, the accurate estimation of pile settlements becomes essential in pile design. The load transfer method (Seed and Reese, 1957) is practical for routine design because of its less computational effort. In the early days, the load transfer methods were based on relationships between the resistance and relative displacement at pile-soil boundaries which are usually referred to as t-z curves. Since these techniques did not consider the deformation of soil around piles, they cannot be applied to the settlement analysis of pile groups.

In this study, a new nonlinear approach for axially loaded piles and pile groups is proposed and validated with field tests and model tests. The proposed method divides the settlement of soil into elastic and inelastic (slippage) components. The inelastic deformation is assumed to occur in a narrow zone around piles while the deformation in the outer zone is determined by an elastic solution proposed by Randolph and Wroth (1978 & 1979). The extension from single pile analysis to pile group analysis is carried out based on the interaction factor concept (Poulos, 1968) together with the reconsideration of the pile-soil-pile interaction by taking the stiffening effect of nearby piles into account. Predictions by the proposed method are well agreed with the validation data, under both of rigid and flexible cap conditions. In addition to the general procedure, a simplify solution is also provided for typical conditions which usually encountered in routine designs.