Abstract: In order to reveal the failure mechanisms of the surrounding rock near caverns considering the influence of structural surface in deep highly-stressed condition, a finite/discrete element method combined approach is adopted to establish the numerical models of circular hole specimen containing pre-existing flaw, with particularly attention paid to the mechanical failure characteristics and the crack growth behaviors around the circular hole under the condition of different locations, lengths and dip angles of pre-existing flaw. A series of targeted supporting measures are put forward for each case. Research results show that (1) For the specimen without pre-existing flaw, extensional cracks will appear on the top and bottom of the hole primarily; then the splitting cracks will gradually emerge and coalesce on both sides of circular hole subsequently, which is similar to the slabbing failure near excavation boundaries. (2) The rocks on this side will present the totally shear-slip failure if there exists exposed pre-existing flaw on either side of the circular hole. Contrarily, it will exhibit tension and shear failure if there exists unexposed pre-existing flaw on either side of the circular hole. The damage degree of specimens containing unexposed pre-existing flaw may be more serious and intense compared with those with exposed pre-existing flaw, and is more prone to induce rockburst. (3) For those flaws where are located on top of circular hole, whether the flaws are exposed or not, the rockmass will present a local caving or collapse eventually. (4) With the increasing length of pre-existing flaw, the failure mode of upper rockmass will be transforming from local caving to global collapse eventually. (5) If the pre-existing flaw is on either side of circular hole, the released kinetic energy(damage degree) during failure process will present the tendency of increase firstly and decrease subsequently with the increasing dip angle of flaw, However, for the condition of pre-existing flaw located on top of circular hole, the damage degree of specimen will be the most intense and serious only when the dip angle of pre-existing flaw reaches 60º. Research results may provide guidance for engineering excavation, support design and stability analysis of rockmass containing flaws and faults.

Key words: finite/discrete element method(FDEM), circular hole, pre-existing flaw, structure surface effect, rockburst, numerical simulation