- Laterally loaded pile groups

Abstract

This thesis is concerned with the problem of determining the response of pile groups to lateral loads. A model study is utilised to provide information on the effects of pile interaction and pile installation. The principal aim of the study was to define the effects of interaction between laterally loaded piles that have been installed by driving. Previous studies have ignored the effects of the installation process. The experimental programme was mainly involved with studying interaction between two piles in dense dry sand. The influence of pile interaction on the lateral load carrying capacity of each pile within the group, has been investigated in detail for various conditions of pile shape and stiffness, head fixity, and sand density. Three approaches were used to assess pile interaction. The first employed a stereophotogrammetric technique to observe the movement of sand particles. The second involved the determination of the lateral load resistance of each pile and the variation in this with pile deflection and pile spacing. Lastly a pile instrumented with pressure transducers was used to obtain the soil pressure distribution against each pile and to observe the changes resulting from pile interaction. Based on the information obtained from the measurement of soil pressures, the general response of sand to pile transmitted lateral loads is discussed. The results are compared with the commonly assumed values of soil stiffness and ultimate pressures. The effect of pile driving on the surrounding soil is studied. The driving process is shown to substantially alter the subsequent lateral response of each pile within the group. Previous model studies and current analytical techniques for assessment of pile interaction are reviewed. An analytical method of allowing for pile interaction, based on the results of the experimental study, is presented. This new technique is considered to give more realistic estimates of pile interaction, especially in the way it affects individual piles within a group. Charts are presented, from which an assessment of the maximum likely effects of interaction can be easily obtained without the need for a rigourous analysis. (TRRL)