Effect of Precast Pile Driving on Liquefaction Potential Mitigation of Sandy Silts Based on CPTu

Abstract

Precast concrete piles are adopted as a foundation solution in liquefiable silty sand and sandy silt layers of north of Oman Sea shorelines for large diameter liquid tanks. The ground water table is about 6 m deep, and a highly potential liquefiable layer is identified from 7 m and continues to about 12 m deep. This liquefiable layer not only reduces the pile shaft skin friction, but also could have caused damage to slender precast piles as a result of kinematic and inertia shear forces and bending moments, in particular at the intersection of liquefiable and non-liquefiable cohesive layers underneath. The main objective of the paper is to evaluate the effect of densification of sandy silt deposits attributed to pile installation and the possibility of liquefaction mitigation effects due to radial compaction of the soil. CPTu tests were carried out prior to and after the installation of piles. It is noticed that both qc and fs were increased depending on the center-to-center spacing of piles. Liquefaction analysis is carried out on CPTu results before and after piling installation and it is observed that the sandy silt layers are significantly strengthened against liquefaction and the safety factor notably rose above unity after the pile driving operation. The results are compared with triaxial cyclic tests on samples taken from a comparable depth for further investigation, indicating that the mitigation has occurred simply with a 10 percent increase in the relative density of the liquefiable sandy silt layer