Hidromechanical simulation in a fractured rock mass: the experimental site of Coaraze (Southern-Alps, France)

Abstract

Hydromechanical processes in large permeable jointed rock masses have been poorly studied due to the difficulties in determining boundary conditions in such large sites. To study this type of problems, in situ field experiments have been carried out since 1997 on a small fractured calcareous rock mass in Southern France, near Coaraze (limestone aquifer). The present work is intended to enhance understanding of hydromechanics in rock masses by testing the stress and strain state of the rock matrix and its discontinuities at the experimental site of Coaraze subjected to a stationary water flow introduced between the discontinuities. This stationary water flow is controlled by a floodgate located on the downstream spring, inducing a hydrostatic water pressure, which is directly opposed to the normal component of the stress in the joint. The water flow directly reduces the frictional strength by dropping the effective stress. The effects of water pressure and lithostatic stress on the deformations are simulated by the application of a two-dimensional computational model called DRAC. The program package DRAC is based on the Finite Element Method (FEM) and it has been developed by the Dept. of Geotechnical Engineering and Geosciences, of the Technical University of Catalonia, and designed for the analysis of rock mechanics and other geotechnical problems. In the present work, its functionability and applicability as a discontinuous method is demonstrated, taking into account separately the behaviour of both the rock (solid elements) and the discontinuities (interface elements). DRAC seems to be a good approach when simulating hydromechanical rock mass processes in large and permeable jointed rock masses.