Report No.: CCEER-00-1
Title: Undrained Lateral Pile and Pile Group Response in Saturated Sand
Authors: Mohamed Ashour and Gary Norris
Date: January, 2000
Sponsoring Agency: State of California Department of Transportation (Caltrans)
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557
Strain wedge(SW) model formulation has been used, in previous work, to evaluate the response of a single pile or a group of piles (including its pile cap) in layered soils to lateral loading. The SW model approach provides appropriate prediction for the behavior of an isolated pile and pile group under lateral static loading in layered soil (sand and/or clay). The SW model analysis covers a wide range over the entire strain or deflection range that may be encountered in practice. The method allows development of p-y curves for the single pile based on soil-pile interaction by considering the effect of both soil and pile properties (i.e. pile size, shape, bending stiffness, and pile head fixity condition) on the nature of the p-y curve. In the SW model analysis, clay is assumed to respond under undrained conditions considering the effect of pore water pressure, and sand is subjected to drained conditions (no excess pore water pressure).
This study has extended the capability of the SW model in order to predict the response of a laterally loaded isolated pile and pile group in liquefiable soil by accounting for the developing excess pore water pressure in sand (undrained conditions) either in the near- or free-field. In order to accomplish such a goal, a series of formulations has been developed to assess the undrained behavior of saturated sand from its drained response, and to predict the potential of sand to liquefy under different circumstances. The SW model has shown the capability to evaluate such soil response due to both the near field pore water pressure around the loaded pile and the free-field excess pore water pressure due to level ground earthquake shaking after Seed.
The undrained results obtained using the SW model are significantly different than the drained results for a pile or pile group driven into a site with liquefiable soil.. The assessed results foretell that the behavior of laterally loaded piles is function of both soil and pile properties and is influenced by the level of pore water pressure build-up in the soil surrounding the pile. The capacity of a loaded pile or pile group might significantly drop under such conditions. (by authors)