A wide study of the medium (roughly 20 m by 20 m by 20 m) sized superficial sandstone bedrock reservoir, namely Coaraze natural site, France, is planned. Laboratory and site experiments will be compared and the data set will be used for simulations with 3DEC/3Flow ITASCA code implemented with later models. A part of the laboratory experiments is presented here. The BCR3D (3D direct shear box) with its hydraulic Sectorized device, and its portable laser beam from 3S (Soil, Structure, Solide) Laboratory, France, is used. The interpretation of the rock matrix characterization tests, of the cyclic mechanical compression test, and the cyclic hydro mechanical compression tests show that the normal stiffness is stress dependent, the initial normal stiffness value, kno= 122 MPa/mm, dependent on the initial fitting of the two joint walls, and the maximum normal stiffness value, knimax= 164.3 MPa/m, is reached at δmax= 0.5 mm of normal displacement.
This study is only the laboratory part of a wider one: model, laboratory and in situ experiments are planned at the Coaraze site, close to Nice, France. The site is a medium (roughly 20 m by 20 m by 20 m) sized superficial sandstone bedrock reservoir (Coaraze natural site, France); with fractures and bedding planes, Cappa et al. (2004).
(Figure in full paper)
The measurement of anisotropic hydro mechanical properties of natural or artificial fractures is possible at the laboratory 3S (Soils, Solids, Structures), using a prototype device called BCR3D (3D Direct Shear Box for Rock Joints). From the mechanical point of view, this machine is equipped with 5 electromechanical jacks, and is fully computer controlled (Figure 1 and Figure 2).
Any history of shearing along two orthogonal directions of the joint, and of normal loading are possible. Any shear paths are possible (specially at constant normal stress and at prescribed normal stiffness). The
(Figure in full paper)
hydraulic anisotropic conductivity of a joint is investigated, during shearing or not, using a radial flow (a radial gradient) with a central pressurized input and 5 independent external outputs at atmospheric pressure (Figure 3).
The maximum input pressure of the fluid is 20 MPa, and the maximum input flow is about I liter per minute. The morphology of the two rock walls can be measured by a laser beam (diameter: 0.25 rnrn, sampling step: 0.15 mm/128 × 128, vertical resolution: 0.0 I mm) at any stage of the loading, without unmounting the sample, only by opening the box. Measurements of the evolution of morphology are possible and performed for the actual study. The computations and interpretations of the evolution of the morphology are not presented here. The quality of the tests (very small relative rotations of the rock walls) is preserved by the kinetic choices: the shearing in one direction is realized by two symmetric movements of the rock walls, due to two opposite jacks (Figure I). Then the normal force is centered at any time on the active part of the joint.