Centrifuge Modeling of Pile-Sand Interaction Induced by Normal Faulting

Abstract

Many forensic studies conducted after catastrophic earthquakes revealed severe damages to pile foundations caused by bedrock fault movement. The mechanism behind these pile foundation failures is not yet fully understood. In this study, two centrifuge model tests are carried out on a single pile and on a group of three piles in sand subjected to normal faulting. The surface settlement profile and additional internal forces of the piles are measured. The surface settlement profile in sand could be well fitted and predicted with a profile function (error function). The single pile, which is located in a differential settlement zone, is displaced, and the pile top rotates toward the hanging wall, inducing an additional bending moment along the pile. The pile group is then forced to rotate toward the hanging wall because the three piles are well connected to the pile cap. Driven by the movement of the two additional piles and a pile cap in place, the pile on the footwall side experiences greater displacement and bending moment than it does when it is only for a single pile. Due to relative downward displacement of the surrounding soil, negative shaft friction is mobilized and the middle pile could fail in tension. Both the downward drag force in the middle pile and the working load are transferred to the other two piles, resulting in pile failure that exceeds the ultimate capacity.