Numerical Analysis of Effects of Fault Rupture on Overlying Soil Structures

This paper deals with the problem of fault rupture propagation through earth structures. Common practice has been to avoid construction of important structures such as dams across faults, but it is not always possible and a number of dams have been constructed over potentially active faults.Since any severe damage to a dam can be catastrophic, it is necessary to gain an understanding of the phenomenon of fault rupture propagation through dams. In this paper, rupture propagation of an active dip-slip fault through clayey soil is modeled numerically. For this purpose a 2D plane strain model of the problem is analyzed by finite element method. The soil is assumed to have an elasto-plastic behavior which obeys the Mohr-Coulomb failure criterion with a non-associated flow rule for more realistic predictions of deformations. Fault rupture propagation is investigated through two representative geometries, a horizontal layer of clayey soil and a section of homogenous earth dam. Numerical results were compared withexperimental observations of 1g tests on clay samples where their good agreements prove the success of a proper elasto-plastic constitutive model in numerical simulation of fault rupture. In the horizontal layer, angle of rupture path while approaching the surface is measured in different cases of fault dip angle for different soil types and found to be meaningful regarding theories of soil mechanics. Through modeling of the earth dam, bending of fault rupture toward the footwall is detected and the angle of fault rupture near the sloping surface is shown to be controlled by slope of the surface. The effect of soil characteristics and fault dip angle are investigated in rupture path formation.