Modeling lateral flow and liquefaction-induced ground movement

Principal Investigator: Ronaldo I. Borja
Project Sponsor: National Science Foundation

Project Summary

The objective of this project is to develop a mathematical model for analyzing the problem of lateral flow and liquefaction-induced ground movement during and following an earthquake. The model is based on a two-phase mixture theory, and involves the development of a finite element code capable of representing the behavior of saturated soils prior to and during liquefaction. Prior to liquefaction, the soil will be represented by a plasticity model with nonlinear kinematic hardening formulated in terms of effective stresses. During liquefaction, the liquefied soil will be represented by a viscoplastic model formulated in terms of total stresses. The two constitutive models will be cast within the framework of finite deformation theory based on multiplicative plasticity.

Two case studies will be considered to validate the model. The first case study involves a loose saturated sample of Toyoura sand submerged in water and sloped inside a test box. The test box was subjected to dynamic excitation, causing the soil to liquefy and flow like a viscous fluid. Data on the input acceleration, pore pressure development, time-history of displacements, and grain size characteristics of the soil are available for this test. The second study involves a re-analysis of the nonlinear ground response recorded by a downhole array in Port Island, a reclaimed ground near downtown Kobe City, during the earthquake of January 17, 1995. Records indicate that the soil at this site had experienced extensive liquefaction during this earthquake. The Port Island problem will be simulated assuming a condition of vertically propagating seismic waves.