Field study of coupled mechanical-hydrological processes in fracture crystalline rock

A series of experiments with a large in-situ cube of fractured metamorphic rock is heavy conducted. The purpose is to better understand the response of jointed rock to loading. One of the fundamental parameters which can be measured in any mechanical testing scheme is displacement. An instrumentation system was developed to measure absolute displacements in the interior of the block during loading, avoiding a suspected decoupled zone near the surface. The system is based on an array of inductive proximity transducers mounted on a rigid reference frame anchored to the mine roof above the block. The stress field within the block during loading was monitored at several points with U.S.B.M. borehole deformation gages, using elastic moduli determine separately at each point with a borehole dilatometer. With these data the effect of fractures on the redistribution of stresses can be more readily understood. Fracture conductivity affects the rate of contaminant migration from repositories to the biosphere. A multiple-zone borehole probe is being developed that simultaneously monitors fracture aperture and conductivity in each zone. A two-dimensional computer model of the test block is being calibrated with the results of the deformation and stress studies. Successful application of such models would create confidence in using them to predict excavation performance