Caractérisation hydromécanique des milieux rocheux fracturés en laboratoire et in situ

Abstract : Risk management related to underground mining (active or abandoned mines and quarries, rock slopes), waste repositories, greenhouse gas storage tanks, water, oil and natural gas resources, needs to be better understood in order to be able to predict the hydro-mechanical behaviour of fractured rock masses. The scientific goals are both the evaluation of the mechanical stability of fractured rock masses and the prediction of fluid flows, given that these two aspects are closely linked. Indeed, the stability of a fractured rock mass depends on the fluid water pressure in the fractures and pores, whereas the permeability of a storage area is affected by the mechanical state of stress surrounding it. The research undertaken by INERIS, in partnership with French university laboratories (“Géosciences-Azur” Laboratory, Nice;“Sols, Solides, Structures” Laboratory, Grenoble; “Environnement, Géomécanique & Ouvrages” Laboratory, Nancy), related to the improvement of the hydro-mechanical characterization of porous and fractured rock masses starting from in situ experiments and laboratory tests. This improvement was made possible thanks to the development of new characterization tools and new interpretation and prediction methods based on numerical modelling. The scientific assets relate to the evaluation of fracture flows and hydro-mechanical couplings from laboratory tests to in situ experiments. A removable device, enabling hydraulic pressure and displacement measurements to be carried out, was developed in partnership with the Géosciences-Azur Laboratory. The device was used in a fractured limestone outcrop located close to the Coaraze village to the North of Nice in France. The experiments consisted in carrying out various pulse tests. In parallel, we developed and used numerical modelling (with 3DEC code) to reproduce and analyze the measurements, which led to questioning the Terzaghi hydro-mechanical relation and the cubic law for fracture fluid flows. Laboratory tests were carried out on limestone samples from the Coaraze site and on sandstone samples from the Bleuville quarry in the Vosges region in France. The“3S” Laboratory has developed a device to study the hydro-mechanical behaviour of individual fractures on the laboratory scale.This device was modified to measure the flow through porous rock mass samples as well. The results of the tests were analyzed by numerical modelling with the 3DEC and VIPLEF/HYDREF codes. The analyses show that the relation between the hydraulic aperture of the fracture and mechanical closure strongly impacts the fracture flow rate predictions. This was related to the fracture roughness evolution. The rock matrix flow rate can also be slightly affected by the fracture hydraulic aperture. The realization of simultaneous flow measurements in both fractures and the rock matrix should enable us to globally evaluate the conceptual approach used.
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Alain Thoraval. Caractérisation hydromécanique des milieux rocheux fracturés en laboratoire et in situ. Rapport Scientifique INERIS, 2007, 2006-2007, pp.86-89. ⟨ineris-01869099⟩

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