Applicability of a constitutive model to jointed block mass

Deformational behaviour of jointed rocks is governed both by the properties of the joints and the intact rock. The applicability of a constitutive model to predict the stress-strain behaviour of a jointed block mass is discussed in this note. The stress-strain curves predicted by the model are compared with the experimental curves from physical model tests. It is observed that the model predicts the tangent modulus of the mass very closely. The failure strains are, however, underestimated, which may be due to the constant value of shear stiffness, resulting in linear stress-strain response by the model. The non-linear response of stress-strain curves can be obtained by using a variable value of the shear stiffness of the joints. A simple approach has been presented to assign variable stiffnesses, based on direct shear test results on joints. It is found that by assuming a variable stiffness the axial strains can also be predicted accurately. The transverse strain, however, remains highly underestimated by the model.