The finite-element method and the discrete-block method have been used to study the defor-mational behaviour of a jointed rock mass subjected to simple shear displacement. Blocks in models with large sizes of block make contact at few points which cause large openings of joints and high stress concentrations in the blocks and surrounding joints. The introduction of more joints into the models evens out the forces, reduces the stresses and causes a gentle type of deformation. From this study, we draw the practical conclusion that joints in rock plinths are eligible for the storage of radio-active waste, if we take into account the effect of simple shear displacement from faulting.