3D Analysis of coupled stress-flow in jointed rock masses using finite element method

Abstract

Redistribution of stresses in jointed rock mass occurs as a result of underground excavation or any other activity that changes the stresses in the region. The alteration in stress pattern leads to changes in porosity or void ratio of rock material as well in the aperture, i.e. closure or opening of the rock joints. The present study proposes a 3-D coupled stress-flow analysis relating the stress and flow by indirect method. Opening or closure of joints due to normal and shear stresses has been considered with due attention to the dilatant nature of rough discontinuities. As a result, the aperture of joint changes and, in turn, the permeability has too. Joint properties including the attitude of joint, stiffness, aperture, spacing and roughness have been taken into account in the derivation of the constitutive laws and the behavior of a tunnel excavated in jointed rock mass has been examined. More disturbances in the contours of hydraulic head and pore water pressure have been observed near the tunnel periphery. The change in permeability upon redistribution of stresses is a function of the opening/closure of the joints. It has also been shown that the orientation and aperture of the joints have a pronounced effect on the fluctuation of the phreatic surface. ©2008, ARMA, American Rock Mechanics Association.