Abstract: The rock drilling core discing in Jinping Hydro-power Station under high geostress environment is investigated. On the basis of summarizing the existing research results, the macroscopic failure characteristics, discing quantity, thickness and characteristics of borehole were described. The core discing mechanism and the field stress condition of the core discing were summarized through numerical simulation.Results show that: 1) during the drilling process, the tensile stress zone crossing rock core is the dominant factor of core discing crack, and the morphology of rock disk is affected by the tensile stress in the core; 2) sufficient field stress is the primary condition of core discing, and higher tensile stress is induced in the core with higher field stress,and also the condition of core discing crack initiation and expansion is more adequate, and the rock disk’s thickness gets smaller; 3) the increase of radial field stress of borehole has a positive effect on the tensile stress induced in the drilling core, and the axial field stress is opposite; 4) the average value of the maximum tensile stress cross line in the core is defined by comparing with the tensile strength of rock, and the formula of field stress in the presence of drilling core discing is deduced.According to the calculation,the critical condition of Jinping marble rock(T_2b) discing crack is that the radial field stress of borehole should be beyond 34.44 MPa.

Key words: borehole, rock core discing, high geostress, Jinping deep rock mass, rock strength