Micromechanical analysis of the interaction of liquefiable soil with a pile foundation

Earthquake induced liquefaction and lateral spreading is a major cause of failure of civil structures during seismic events. Loose saturated granular soil deposit liquefy when subjected to strong earthquake motion. Such soil experience a decrease in void volume and consequently water pressure in the pores increases reducing the soil effective stresses. During liquefaction, granular soils lose their shear strength reducing dramatically the soil bearing capacity and leading to the failure of civil structures. If a soil deposit is initially sloped, the liquefied granular soil may move substantially down slope, causing Lateral Spreading.In this study, a coupled micro-mechanical model was developed to analyze the response and interaction of a pile foundation with a liquefying and laterally spreading soil. The interstitial pore fluid was idealized using averaged Navier-Stokes equations and the discrete element method was employed to model the assemblage of soil particles. Established semi-empirical relationships were used to idealize the interphase momentum transfer between particles and fluid. The coupled meso-micro mechanical model mentioned above was further developed to handle fluid flow through the soil mass in the presence of subsurface obstacles such as pile foundation. The pile foundation was modeled using the finite element method based on the Bernoulli beam theory. The pile interacts with both the surrounding soil particles and pore fluid. A non-linear Hertz-Mindlin contact relationship was used to model the contact relationship between pile and soil. The pore fluid flow in the vicinity of the pile and the interaction of the pile foundation with saturated soil were verified using experimental observations.The developed coupled micro-mechanical model was used to analyze the response of a saturated granular soil-pile system on a sloping ground. Numerical simulations were also conducted to analyze the liquefaction response of free field level ground and sloping ground deposits. Periodic boundary conditions and a high gravity field were used in order to reduce the number of particles to a computationally manageable value. A dynamic base excitation was applied at the base of the deposit. The conducted simulations provided valuable information on a number of salient micro-scale responses of the soil-pile system during liquefaction and lateral spreading. In qualitative terms, the conducted numerical simulations of of pile foundation interaction with soil during liquefaction exhibited a response pattern consistent with that described in published experimental results. The proposed coupled micro-mechanical model was shown to be an effective tool to investigate the interaction response of a pile foundation with liquefying and laterally spreading soil.