Seismic Lateral Response of Piles in Liquefying Soil

Abstract

Soil liquefaction is one of the major factors affecting the behavior of piles founded in seismically active areas. Although methods are available for seismic analysis of pile foundations, in many of them, the supporting soil is assumed to be an elastic material. Here a numerical model is presented which takes into account the reduction of soil stiffness and strength due to pore pressure generation and subsequent soil liquefaction, in addition to the material nonlinearity. Results obtained from the new method are compared with centrifuge test data and show excellent agreement with the observed pile behavior during these tests. To investigate the effects of soil liquefaction on the internal pile response, a parametric study is carried out for a range of material and geometric properties of the pile and surrounding soil. The effect of the nature of the earthquake on pile performance has been studied using 25 earthquake records scaled to different acceleration levels. It is shown that the "Arias intensity" and the natural frequency of the earthquake ground motion have a significant influence on the pile performance in liquefying soil. Existing elastic analysis methods for kinematic pile loading in layered soil deposits with soft and stiff layers are applied to the soil deposits with liquefying and nonliquefying layers. It is found that these simple design methods, which were derived assuming that the soil is a linear elastic material, do not predict bending moments accurately when nonlinear behavior of soil and effects of pore pressure generation are significant. Also a simplified limit equilibrium method proposed for the evaluation of bending response of single pile foundations subjected to lateral spreading is compared with the bending response obtained from the proposed numerical model. It is found that the limit equilibrium method, which is developed based on the centrifuge test results, does not give accurate results when the pile diameter and the thickness of the liquefied soil layer deviates from the values used for the centrifuge tests.

Response of a RC pile group in liquefiable soil: A shake-table investigation

“…Piles can be damaged further where a liquefiable soil layer is overlaid by a non-liquefiable layer. These observed damages suggest that a deeper understanding of the failure mechanisms of pile foundations during seismically-induced liquefaction is needed [2,[13][14][15][16].…”

Effect of Liquefaction on Soil Pile Interaction under Seismic Loading

“…A small lens of liquefiable layer sandwiched between the non-liquefiable strata can also cause great deflections and failure in pile [7]. Referring to Figure 4, it can be stated that when a lens of liquefiable layer is sandwiched between layers with least liquefaction potential produces a concentration of shear at the interface of two layers on the pile and the soil above this surface flows which is termed as "crust flow".…”

Lateral response of pile foundations in liquefiable soils

“…This pseudo-static method has been suggested early by Miura et al (1989), Miura and O'Rourke (1991), Liu and Dobry (1995), JRA (1996), AIJ (1998) and recently by Liyanapathirana and Poulos (2005) and Elahi et al (2010). This method for pile seismic analysis sometimes underestimates, and sometimes overestimates shears, moments and deflection of the piles.…”

“…During past earthquakes, because of inadequacy of the pile to sustain large shear forces and bending moments, the extensive damage in liquefiable soil has been caused due to both lateral ground movement and inertial loads transmitted to piles. Under earthquake loading, the performance of piles in liquefied ground is a complex problem due to the effects of progressive buildup of pore water pressures and decrease of stiffness in the saturated soil (Liyanapathirana and Poulos, 2005). These effects involve inertial interaction between structure and pile foundation, significant changes in stiffness and strength of soils due to increase of pore water pressures, large lateral loads on piles, kinematic interaction between piles and soils, nonlinear response of soils to strong earthquake motions, kinematic loads from lateral ground displacements, and inertial loads from vibration of the superstructure (Bradley et al, 2009;Gao et al, 2011).…”

“…In Winkler models, p-y curves are used to define the behavior of the nonlinear spring at any depth. These p-y curves can be obtained from the results of model tests or field (Liyanapathirana and Poulos, 2005). The Winkler assumption is that the soilepile interaction resistance at any depth is related to the pile shaft displacement at that depth only, independent of the interaction resistances above and below (Wilson, 1998).…”