The work discusses the processes that can be present at fractures and defects at geological interfaces. The introductory comment clearly indicates that the computational approaches offer the most appropriate methods for examining complex contact problems at geomaterial interfaces. There are, however, certain types of contact problems that are amenable to analytical treatment. The paper examines the problem of a circular dilatant-frictional patch located at an otherwise frictionless interface. The dilatancy processes are induced at the circular patch by the relative shear of the elastic regions. The paper presents a mathematical approach for the study of the problem where results from the solution of integral equations applicable for the internal indentation of a penny-shaped crack by a rigid inclusion and the internal pressurization of an annular crack are combined with a work-dissipation relationship to examine the mechanics of the interactions at the dilatant zone.