Excavation Disturbed Zone: Assessment of Its Hydraulic Properties Based on Surface Investigations

Abstract

ABSTRACTThe approach followed by Nagra for the assessment of the hydraulic properties of the excavation disturbed zone (EDZ) around a potential future underground repository site for low-level and medium-level short-lived radioactive wastes is presented. In the approach particular emphasis was placed on assessing, under realistic-conservative assumptions1, an appropriate way to represent the EDZ within the context of performance assessment (PA). Calculated stress changes due to the openings were mapped onto changes of the mechanical aperture of the rock fractures. The resulting changes of hydraulic properties of the EDZ were then computed, with analytical (simple, continuum-type approximation) and numerical (fracture network representation) methods. The results of both computations were used as the basis to: i) provide hydraulic properties for the EDZ used in PA models; ii) assess whether these properties are conservative, i.e., higher values than expected, or not.