Behavior of Pile Foundations in Laterally Spreading Ground during Centrifuge Tests

TLDR

The study used eight dynamic centrifuge models on a 9‑m radius rig, testing single piles (0.36–1.45 m diameter) and pile groups (0.73–1.17 m) in a layered soil profile of nonliquefied crust over liquefiable loose sand and dense sand, subjected to realistic earthquake motions (0.13–1.00 g), and evaluated procedures for estimating total horizontal loads on piles and caps. The data show that lateral loading directions depend on pile deflection mode, soil profile shape, pile stiffness, and crust load magnitude, and that liquefaction of the sand layer causes the displacement needed to mobilize peak horizontal loads to be much larger than static tests predict.

Abstract

Eight dynamic model tests were performed on a 9 m radius centrifuge to study the behavior of single piles and pile groups in liquefiable and laterally spreading ground. Pile diameters ranged from 0.36 to 1.45 m for single piles, and from 0.73 to 1.17 m for pile groups. The soil profile consisted of a gently sloping nonliquefied crust over liquefiable loose sand over dense sand. Each model was tested with a series of realistic earthquake motions with peak base accelerations ranging from 0.13g to 1.00g . Representative data that characterize the important aspects of soil–pile interaction in liquefiable ground are presented. Dynamic soil–pile and soil–pile cap forces are backcalculated. Directions of lateral loading from the different soil layers are shown to depend on the mode of pile deflection relative to the soil, which depends on the deformed shape of the soil profile, the pile foundation stiffness, and the magnitude of loads imposed by the nonliquefied crust. Procedures for estimating the total horizontal loads on embedded piles and pile caps (i.e., passive loads plus friction along the base and sides) are evaluated. Due to liquefaction of the sand layer beneath the crust, the relative displacement between the pile cap and free-field crust required to mobilize the peak horizontal loads is much larger than expected based on static pile cap load tests in nonliquefied soils.