Lacunar fractality of the contact domain in a closed rock fracture

The correct evaluation of the shear behaviour of rock joints is of fundamental importance in slope stability analysis. A strong size-dependence of shear strength has been detected. The study of the force exchange mechanism at the joint interface, supported by the proper description of the contact domain, represents the mean to provide a size-independent definition of the frictional parameters. In this work, the topography of a real fracture surface in a rock sample has been digitised by means of a laser apparatus. The behaviour of the rock joint under normal loading has been studied, by means of a numerical model, for different shear displacements of the initially matching surfaces. The crack closure laws and the dilatancy curves relating shear displacement to normal opening of the interfaces, have been analysed. Also, the lacunar fractality of the true contact domains is evidenced.