Influence of interface roughness on dynamic shear behavior in jointed rock

An interlock/friction model is used to predict the behavior of natural jointed rock specimens subject to static normal stress and dynamic shear. The friction part of the model is based on the simple Coulomb friction formulation. The interlock part of the model is shown to be related to the degree of interface matching that is present between two surfaces of a jointed rock pair. The interlock/friction model adequately predicts the offset phenomenon in the hysteresis results of well-matched jointed rocks. The offset phenomenon is recognized as an increase in shear stress required for shear displacement away from the naturally-aligned rock positions and a decrease in shear stress upon shear displacement back toward the naturally-aligned location. The parameters of the interlock/friction model are shown to be empirically related to rock interface roughness properties. Prediction of the shear stress vs shear displacement hysteresis including the offset phenomenon is possible for welded tuff specimen pairs using the measured interface roughness amplitude and the interface coherence between jointed rocks. Model parameters were verified by an experiment on molded mortar specimens. The data from the mortar specimens indicate that the empirically determined relations may be valid for jointed rock pairs that have dramatically different strength properties than welded tuff. (C) 1998 Elsevier Science Ltd. All rights reserved.