Failure mechanism and setback distance of single pile subjected to normal faulting

Field case studies after earthquake show that pile foundation can be severely damaged by bedrock fault movement. The failure mechanism of this type of foundation damage is not yet fully understood. Centrifuge modeling of a single pile damage induced by normal faulting in sand is conducted. The deformations of pile and soil are measured. The developments of axial forces and bending moments along the pile with bedrock fault movement are monitored. The centrifuge test results show that when the bedrock fault movement equals 0.4 m, the pile displaces consistently with the surrounding soil. With the increase in bedrock fault movement, sand deformation is localized around a fault rupture and pile displacement is significantly reduced. The rupture increases in dip at the soil-bedrock interface and propagates upward with a dip angle of 80 degrees to the horizontal. It outcrops at the ground surface on the hanging wall side of the pile. The sand deformation is classified as a stationary zone, a shearing zone and a rigid body zone. When the single pile is located around the shearing zone, the pile is bent towards the hanging wall. For normal faulting, the setback distances of a single pile from the bedrock fault line on the footwall and the hanging wall are 15 and 10 m, respectively.