Model Studies on Mechanics of Jointed Rock

A generalized physical model is tested triaxially in order to relate properties of the intact material and of the discontinuities to the strength and deformability of a jointed rock mass. The behavior of jointed models can be divided into three characteristic zones. At low confining stresses there is either sliding along preexisting joints or brittle failure through intact material and across joints with strength depending on the number of intersected joints. At intermediate confining stressed sliding or failure may occur again, but the failure mode changes from brittle to ductile. At high confining stresses no sliding and only ductile failure occurs. The three zones and the upper and lower bounds of strength are easily obtained by a few confined compression tests on the intact material, by sliding tests along joints, and by a direct tension test. If this characteristic behavior is valid for other materials, as seems likely because of the basically similar underlying mechanism, it may become possible to determine the behavior of a jointed rock mass by relatively simple experiments.