Jacked Piles in London Clay: Interaction and Group Behaviour Under Working Conditions

Abstract

This Paper describes a field investigation of the behaviour of a row of two piles and a row of three piles installed at close spacings in London Clay. It follows directly the paper by the same authors (1979) presenting observations of the shear stresses and shear strains around a single pile and the measurement techniques described in that paper have been employed and extended. The three pile row was tested under conditions of equal pile loading and equal pile displacement and also with the piles linked by a rigid concrete cap on the clay surface. In theoretical studies of pile group behaviour the principle of superposition is frequently applied to soil stresses and displacements in order to determine the settlement of each pile in the group. The measurements reported in this Paper demonstrate the validity of a superposition approach both to the estimation of the pile settlements and to the determination of the load carried by each pile. The results of theoretical studies have generally been presented in the form of interaction factors relating the additional settlement caused by a loaded pile nearby to the settlement of each pile under its own load. Interaction factors measured in the field investigation are compared with published theoretical values and also with observations of the variation of vertical displacement of the soil with radial distance from the pile axis. Design curves relating the settlement of piled foundations to the settlement of a single pile are presented. The variation of load transfer along each pile shaft with the complexity of the foundation is discussed. © 1980, Thomas Telford Ltd. All rights reserved.