INFLUENCE OF INTERFACE ROUGHNESS ON DYNAMIC SHEAR BEHAVIOR IN JOINTEDROCK

An interlock/friction model is used to predict the behavior of natural jointed rock specimens subject to static normal stress and dynamic sh ear. The friction part of the model is based on the simple Coulomb fri ction formulation. The interlock part of the model is shown to be rela ted to the degree of interface matching that is present between two su rfaces of a jointed rock pair. The interlock/friction model adequately predicts the offset phenomenon in the hysteresis results of well-matc hed jointed rocks. The offset phenomenon is recognized as an increase in shear stress required for shear displacement away from the naturall y-aligned rock positions and a decrease in shear stress upon shear dis placement back toward the naturally-aligned location. The parameters o f 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 poss ible for welded tuff specimen pairs using the measured interface rough ness amplitude and the interface coherence between jointed rocks. Mode l parameters were verified by an experiment on molded mortar specimens . The data from the mortar specimens indicate that the empirically det ermined relations may be valid for jointed rock pairs that have dramat ically different strength properties than welded tuff. (C) 1998 Elsevi er Science Ltd. All rights reserved.