Liquefaction and lateral soil movement effects on piles

This research work deals with the analysis of single pile response to lateral spread caused by soil liquefaction. A simplified yet rational method of estimating pile loads resulting from lateral movement of liquefied ground has been proposed. The numerical implementation of the model is achieved through the finite element program, B-STRUCT, developed at Cornell University. Centrifuge tests performed at Rensselaer Polytechnic Institute (RPI) to study similar phenomenon have been an integral part of this research. These tests were used to develop and verify the proposed model.;The current methods for estimating pile loads due to lateral spread involve application of empirical coefficients to p-y curves to account for the loss of strength due to liquefaction. It has been demonstrated in this thesis that such degradation coefficients are not unique and depend largely on the p-y model chosen for the unliquefied soil.;To reduce the level of empiricism involved in the design method, a p-y model is developed that is consistent with the undrained behavior of loose sand during liquefaction. Using available results of triaxial extension and simple shear tests performed on loose sand specimens, a p-y interaction model to simulate the conditions during lateral spread has been proposed. The proposed p-y curve is trilinear in shape with a peak and a steady state soil reaction corresponding to the peak and the steady state strength of the sand during liquefaction. The model was validated by comparing the analytical prediction with the results from centrifuge tests performed at RPI and also against observed pile damage resulting from lateral spread during the 1964 Niigata earthquake.;Although the main focus of this research is on pile response to lateral spread, a set of dimensionless solutions based on the subgrade reaction model has been developed to analyze pile response to lateral ground movement. The dimensionless solutions have been formulated to include nonlinear soil response, effects of axial load and axial load transfer. From the results of dimensionless analyses, the conditions of rigid pile behavior were identified.;Three failure modes for rigid piles recognized under lateral soil movement are soil flow failure, rotational failure, and base failure. Design guidelines are presented for identifying different failure modes and for safe design of piles against excessive lateral movement.