Bentonite rock interaction experiment: A hydro-structural-mechanical approach

Abstract

Deformation zones and fractures are of major importance to engineering and to the characterisation of the mechanical- and hydraulic behaviour of rock. In this paper we demonstrate how structural mapping can provide key information on fracture sets and their properties, and how it can be used to investigate conformity between different working scales. This is shown by the detailed structural mapping related to the experiment “BRIE” - Bentonite Rock Interaction Experiment. “BRIE” was carried out in a tunnel of the Äspö Hard Rock Laboratory, Sweden, in crystalline rock. The implemented approach relied on a multidisciplinary and trans-stadial investigation to compile and interpret all the hydrogeological, structural and rock mechanical constraints as inputs to modelling. To this end, available data from all BRIE construction- and experimental stages were used to characterise natural and induced rock stresses. Results from detailed structural mapping of the tunnel and drill cores recovered from the tunnel floor were key for sound rock mechanical modelling and were successfully integrated with the available hydrogeological observations. Structural mapping was used to define five systematic fracture sets, key fractures and their properties (size, friction angle and normal stiffness) and to establish a simple deformation history. Furthermore, the structural features exposed in the studied tunnel and in the logged BRIE cores were compared with those of an adjacent Äspö HRL tunnel. Both sites structurally fit the sub regional tectonic framework, thus showing conformity between very different observation scales.