Determination of Regional Stress by FEM for Rock Mass with a Fault

Abstract

Stress measurements may give us only local stresses, which are affected by heterogeneity of rock mass, discontinuities and surface topography. Therefore, it is necessary to determine regional stress from limited data of local stress for estimating stress distributions in a region under consideration for various engineering projects such as underground repository of high-level radioactive wastes.
In this study, regional stress in a rock mass with a penetrating fault was defined as displacements at the boundaries as a function of the coordinates, which are different for the upper and lower rock bodies to allow relative displacements of the fault. The fault was modeled by joint elements with 16 nodes, and a condition for frictional sliding was given by Coulomb' s criterion. First, by using a small-scale model having a fault, the effects of frictional sliding of the fault on the distributions of both stress in the rock mass and the shear stiffness of the fault were investigated. Next, based on the results, we proposed a method for determining regional stress with a 3-D finite element method from stress data measured along a line that penetrates the fault. It was shown that the stress distribution in a region under consideration can be estimated by the method when a sliding area of the fault is less than half of the whole area, although the estimation becomes poorer as the sliding area increases.