Abstract:Brittle failure with slabbing and spalling as a dominant failure mode of surrounding rock is a typical failure phenomenon in deep hard rock masses due to excavation activity. On the basis of brief introduction and comparison of four different approaches for modelling failure of brittle hard rock masses, the numerical tests of in-situ compression and uniaxial compression of hard rock pillars were carried out by means of FLAC^3D based on the DISL method. The applicability of the DISL method was discussed and the brittle failure processes and characteristics of hard rock pillars were further explored. The results show that, in the in-situ compressive simulation, when the total unloading step is greater than a critical value, V-shaped failure occurs on both sides of the pillar, and the pillar forms an hourglass shape as a whole. Under different homogeneity indices, the yield elements are mainly distributed in and around V-shaped failure area and their distribution range is controlled by low confining pressure zone and tension zone. The V-shaped shear band is dominated by tension-shear failure and accompanied by tension failure elements in the inner part close to the pillar side wall. In the uniaxial compressive simulation, V-shaped failure still occurs on both sides of pillar in post-peak stage and the range of tension fracture is limited by shear band.

Key words: hard rock pillars; brittle failure; numerical simulation; DISL method; failure modes; strength characteristics