The presence of discontinuity in the geological media has long been recognized as an important factor influencing the mechanical behavior of the media. This paper proposed a versatile constitutive law that can model an assemblage of intact rock blocks separated by cleavage, bedding planes, joints, or other types of structural weak planes. The constitutive law is capable of modelling any number of joint sets with arbitrary orientations. Applicability of the model are evaluated by comparing the predicted results with existing model predictions. The effects of joint numbers, and joint orientations are also discussed.