Abstract: In order to simulate the transition of rock from continua to discontinua more accurately and reduce the mesh dependence, an element splitting method is developed based on the continuum-discontinuum method where the Lagrangian element method is coupled with discrete element method. The computational domain is discretized into high-precision quadrilateral elements; after cracking, the cracks can propagate along the diagonal lines of quadrilateral elements and the edges of triangular or quadrilateral elements. Deformation-cracking processes of the Brazilian disc rock specimen, uniaxial compression rock specimen and surrounding rocks under hydrostatic pressure are simulated. The following results are found. (1) For the Brazilian disc rock specimen, tensile cracks propagate from the center of the disc to the top and bottom until they penetrate through the disc, and the tensile cracks are relatively smooth; for the uniaxial compression rock specimen, shear cracks are relatively straight, and the direction of the main shear crack penetrating through the rock specimen is consistent with the shear plane direction obtained according to the Mohr-Coulomb criterion. (2) From the effects of hydrostatic pressure and internal friction angle on deformation-cracking processes, the following results are found. Under hydrostatic pressure, firstly, V-shaped notches appear near the cavern surface due to shear crack propagation; then, long and curved shear cracks appear due to further shear crack propagation whose distribution is similar to shear slip-lines. With an increase of hydrostatic pressure, the ranges of shear cracks increase, whereas with an increase of internal friction angle, the ranges of shear cracks decrease, and the angle between the propagation direction of the long shear crack and the annular direction decreases. (3) According to the simulation of the surrounding rock in phase-Ⅱ Tianshengqiao hydropower station, four V-shaped notches are observed, which is in a good agreement with field observation.

Key words: mesh dependence, cavern surrounding rock, deformation-cracking process, hydrostatic pressure, internal friction angle, shear slip-line