Modeling of complex geological rock mixtures under triaxial testing conditions

Complex geological mixtures of rock inclusions randomly distributed in a weaker matrix can raise challenging issues for a proper geomechanical characterization. These materials, also referred as bimrocks, are widespread all around the world and can be recognized in a vast range of geological formations. Although most of these formations are assumed to be controlled by the matrix mechanical properties, several studies, instead, showed that the overall behavior is strongly influenced by the presence of the rock fragments and, in particular, by their volumetric content. In the present study, the overall mechanical behavior and strength characteristics of rock mixtures during triaxial tests were studied using a 3-D finite element. A script routine was specifically developed for the 3-D model generation. Given a specific volumetric content and preferred inclusion orientation, the routine generates cylindrical specimens with ellipsoidal inclusions. Ellipsoidal surface intersections are governed by applying an algebraic separation condition which states the contact condition between two inclusions (i.e., separated, overlapped, or overlapped at a single point). The preliminary FEM analysis on specimens with spherical inclusions indicated a marked influence of the inclusion’s volumetric content on the mechanical properties of the bimrock. Different behaviors were observed for welded and unwelded specimens. Further studies will focus on the effect of ellipsoidal inclusions.