The Behavior of Piles Driven in Clay. I. An Investigation of Soil Stress and Pore Water Pressure as Related to Soil Properties

Abstract

This paper outlines research on large model piles and some full-scale piles driven into insensitive clay to study the phenomena of load transfer and the effect of pile driving on the soil. It is divided into two parts. Part I deals with the stress field set up by driving a large model pile into an instrumented clay bed and the stresses measured for some full-scale timber piles. Part II presents an evaluation of the load carrying capacity of the model pile and compares the results with full-scale pile load tests. The soil properties are evaluated in terms of effective stress for an estimate of the bearing capacity of the piles.The measured soil displacements near the shaft and base agree well with plastic theory, while the observed magnitude of the pore pressures in the clay due to driving are smaller and the rate of pore pressure dissipation is greater than expected theoretically.The magnitude of the total and effective radial stresses surrounding the pile is mainly related to the stress changes in the soil due to placing the pile and subsequent stress changes are relatively small. On the other hand, the tangential and vertical stresses vary appreciably with time and the latter stresses depart considerably from estimates based on elastic theory, due to locked-in-soil stresses.An approximate theory is presented to estimate the average effective radial stress on the pile shaft in connection with the ultimate shaft capacity. This proposed approach is supported by observations in some clays of low sensitivity, but requires further research in other type of clays.