EDZ development in indurated clay formations – In situ borehole measurements and coupled HM modelling

Underground excavation induces a disturbed/damaged zone around the opening. In argillaceous rock, the excavation disturbed zone may be influenced not only by rock mechanical properties (in situ stress state, rock strength) and excavation methods, but is also strongly controlled by hydro-mechanical properties (desaturation, anisotropy). To characterise the excavation disturbed zone at the Underground Research Laboratory Meuse/Haute-Marne (France), different geoscientific methods, as hydraulic gas tests, seismic borehole measurements, borehole video recording, and core mapping have been used in six fan-shape arranged boreholes within the frame of the KEY1 experiment.The results from different methods correlate quite well. In this test location the extent of the excavation disturbed zone with an increased permeability of 1 × 10−16 m2 is about one diameter of the drift in the bedding direction and half a diameter of that in the normal direction to the bedding, which forms to an ellipse. The ellipse-shape distribution of the increased permeability zone around the drift may be explained using a coupled hydro-mechanical model taking the hydraulic and mechanical anisotropies into consideration. This was already intensively studied based on the measured data and in situ observations from the Mont Terri Rock Laboratory (Switzerland).