Soil Behavior for Piles Under Lateral Loading
Authors: O&apos;Neill M.W. , Reese L.C. , Cox W.R. 
Published: October 2008

This paper reviews recent research into the behavior of laterally loaded piles and pile groups in clay and sand. The focus is upon cyclically loaded driven piles in over consolidated soil, both clay and sand. Criteria and phenomenological observations are discussed that are intended to be provide guidance to designers of foundations for offshore structures.

INTRODUCTION

Current design criteria for laterally loaded piles are based upon full-scale loading tests conducted mostly in the 19S0's and 60's, supplemented with more recent analytical investigations. During the 1980's a number of new studies were conducted on full-scale piles and pile groups, and other studies, not released earlier, were published. This paper summarizes succinctly those studies that have been performed and reported elsewhere by the authors and emphasizes patterns among the various studies. Lateral pile behavior will be discussed according to (a) Over consolidated clay (single piles and groups) and (b) over consolidated sand (single piles and groups). Design observations are given primarily in terms of the "p-y" concept that is commonly used in analyzing laterally loaded piles (1).

OVER CONSOLIPATED CLAY

Single Piles. Reese et al. (1) suggested a criterion for p-y curves in over consolidated clay below a free water surface. That criterion, which is based on static and cyclic loading tests on piles of varying diameters up to 24 in., prescribes very significant degradation of the soil after the peak displacement has been reached. One reason for the large degradation may have been that the soil at the test site was moisture deficient, in a geologic (long term) sense and that testing prompted softening beyond that which might be expected in a typical offshore deposit. Practitioners have often applied a p-y criterion proposed by Matlock (2) for soft clay (using parameters for stiff, over consolidated clay) in order to avoid specifying sharp post-peak degradation. For large-diameter piles, modifications, such as those proposed by Stevens and Audi Bert (3) or Gazioglu and O'Neill (4) are often used, because both Matlock's criterion and the criterion of Reese et al. (1) specify a deflection control parameter to be linearly dependent on pile diameter, which appears to predict excessive deflection in piles of very large diameter.

A new set of tests reported by Donavan and O'Neill (S) was conducted under a free water surface at the University of Houston at a test site consisting of over consolidated clay with a natural water table very near the base of the test pit. Pile diameters ranged from 1O.7S in. to 72 in. Donavan and O'Neill proposed a new "stiff clay" criterion based upon these tests. In this criterion the term ySO' the pile deflection corresponding to one-half of the maximum static soil resistance, P max (static), is not linearly dependent on the pile diameter. The manner of expression of this nonlinear effect is that developed by Gazing and O'Neill (4), which depends upon the relative stiffness of the pile and soil. (MATHEMATICAL AVAILABLE IN FULL PAPER)