Liquefaction-induced settlement of the pile group under vertical and horizontal ground motions

Abstract

End-bearing piles have been widely used to resist earthquake-induced settlement of buildings in sand deposits. However, the earthquake can generate the excess water pressure in saturated sand deposits and thus reduce both the friction resistance and end-bearing capacity of piles, further resulting in the pile settlement which may not be sustained by the superstructure. In this study, a fully coupled dynamic effective-stress finite element procedure is used to investigate the effects of the frequency content of input motion and the amplitude of both horizontal and vertical components of input motion on the settlement of the pile group in saturated sand deposits. A modified generalized plasticity model is employed to characterize the dynamic behavior of various density of sands. The effect of the soil permeability on the seismic response of the pile-soil system is investigated. The results indicate that the relatively distant earthquake cause more severe liquefaction at the sand deposit than the nearby earthquake and thus induces more settlement of the pile group under otherwise identical conditions. Moreover, the vertical ground motion could significantly increase the coseismic liquefaction-induced settlement of the pile group (ρE) and should be taken into account in engineering design. A simplified practical method based on the load-transfer methodology is proposed to estimate the ρE for the pile group with the cap above the ground.