Characterization of Joint Set Effect on Rock Pillars Using Synthetic Rock Mass Numerical Method

In this paper, a synthetic rock mass (SRM) method is used to numerically characterize the effect of joint sets on rock pillars. The SRM model is constructed by explicitly inserting discrete fracture network into a particle assembly. Conceptual SRM models show that pillar-loading capacity is weakened by inserted joints. Pillar peak strength is lower when inserted joints favor shear sliding of rock blocks, and strength becomes higher when pillar failure is controlled by fragmentation of intact rocks. Meanwhile, loading capacity is weakened when longer joints are simulated. The effect of joint sets on pillar modulus is similar to the observed effect on peak strength. Pillar failure behaves as a continuous shear failure when the inserted joints are inclined and changes into intact rock splitting when the joints become vertical. The SRM method is then used to characterize the joint set effect on real pillars in the Doe Run mine. A pillar model with a width/height ratio of 0.8 is initially constructed on the basis of derived joint characteristics from photogrammetric mapping. Numerical results show that the pillar peak strength and deformation modulus were reduced by 68.1 and 44.8%, respectively, in comparison with the corresponding properties of the joint-free model. A series of additional pillar SRM models is also studied, and SRM pillar strengths agree with the empirical formulas in general. Finally, this paper presents a comparison study between continuum and SRM models. The coincidence in findings between the two numerical methods further validates the robustness of the SRM method for characterizing joint set effect on rock pillars.