USE OF THE DISTINCT ELEMENT METHOD TO PERFORM STRESS-ANALYSIS IN ROCK WITH NONPERSISTENT JOINTS AND TO STUDY THE EFFECT OF JOINT GEOMETRY PARAMETERS ON THE STRENGTH AND DEFORMABILITY OF ROCK MASSES

To use the distinct element method, it is necessary to discretize the problem domain into polygons in two dimensions (2 D) or into polyhedra in three dimensions (3 D). To perform distinct element stress analysis in a rock mass which contains non-persistent finite size joints, it is necessary to generate some type of fictitious joints so that when they are combined with the non-persistent joints, they discretize the problem domain into polygons in 2 D or into polyhedra in 3 D. The question arises as to which deformation and strength parameter values should be assigned to these fictitious joints so that they behave as intact rock. In this paper, linear elastic, perfectly-plastic constitutive models with the Mohr-Coulomb failure criterion, including a tension cut-off, were used to represent the mechanical behaviour of both intact rock and fictitious joints. It was found that, by choosing the parameter values for the constitutive models as given below, it is possible to make the fictitious joints behave as intact rock, in a global sense. a) For both the intact rock and the fictitious joints, the same strength parameter values should be used. b) A joint shear stiffness (JKS) value for fictitious joints should be chosen to produce a shear modulus/JKS ratio (G/JKS) between 0.008 and 0.012 m. c) A joint normal stiffness/JKS ratio (JKN/JKS) between 2 and 3 should be chosen. The most appropriate value to choose in this range may be the Young's modulus/G value (E/G) for the particular rock. Some examples are given in the paper to illustrate how to use the distinct element method to perform stress analysis of rock blocks which contain non-persistent joints and to study the effect of joint geometry parameters on strength and deformability of rock masses.