Seismic behavior of pile-supported systems in unsaturated sand

The seismic behavior of pile-supported systems has been an active area of research over the past decades. However, focus has mostly been on evaluating the seismic response of structures embedded in either dry or fully saturated soil conditions. In this study, series of dynamic centrifuge tests were conducted to investigate the effects of soil's degree of saturation on the seismic behavior of pile-supported superstructures. The scaled physical model tests were carried out on two distinct pile-mass systems embedded in uniform sand layers. A steady state infiltration technique was used to control matric suction profiles in the sand layer prior to shaking. The obtained results from these experiments were illustrated in terms of peak accelerations, peak lateral displacements, and frequency content of the structural motion. The observed response showed higher acceleration amplification and lower lateral deformation for the pile-supported systems with foundations embedded in unsaturated sand comparing with those in dry sand. An inverse simple pseudo-static analysis was performed to back-calculate soil modulus values from the pile lateral deformations. The calculated values of soil modulus were higher for unsaturated sands showing consistency with the effect of matric suction on increasing the soil stiffness.