Shear Strength Behavior of Mont Terri Opalinus Claystone in Fault Zone

Abstract

The paper summarizes the results of direct shear strength tests carried out on Opalinus Claystone deriving from a fault zone, at the site of Mont Terri (North-Western Switzerland). In Mont Terri an Underground Rock Mechanical Laboratory is conducting studies aimed at specifying the rock mechanical parameters of the rock surrounding, which is at the same time the potential host rock of a highly active radioactive waste disposal facility. The samples for the tests were derived from blocks and cores collected from the main fault zone, during the excavation of a tunnel, named: Full scale Emplacement demonstration experiment Gallery (FE Gallery). Direct shear strength tests were carried out on 50x50 mm samples undergoing a 1 MPa constant normal load, where the natural shear plane was parallel to the direction of the shear. The orientation of the bedding planes in the samples was recorded and the maximal shear strength and residual shear stress were determined. The maximal shear strength values obtained from the tests fell in the interval 0.34-0.78 MPa, while the residual values fell between 0.31 and 0.72 MPa. The effect on the shear strength of different angles defined by the bedding and the shear plane of the samples was also examined. The bedding of the samples enclosed different angles with the shear plane, ranging from 0 to 49 degrees.