Abstract: The crack propagation process and failure mode of discontinuous jointed rock mass with different roughness coefficients under different normal stresses are studied via particle flow method, and the stress evolution process of pre-shearing plane is discussed. Results reveal that the failure modes of rock bridge can be roughly divided into five categories according to the tensile and shear properties of micro-cracks and their evolution process, which are closely related to the normal stress and joint surface roughness coefficients. The increments in normal stress and joint surface roughness coefficients would instigate rock bridge towards shear failure. The angle between the initial wing crack and the original joint surface is not sensitive to the change of normal stress; but declines with the increase of joint roughness coefficients. In the shearing process, the stress on the pre-shearing plane does not distribute uniformly and meanwhile redistributes continuously. The shear stress of flat jointed rock mass is mainly borne by rock bridge, and the compressive stress of the rock bridge is greater than that of the joint in both horizontal and normal directions, while for rough jointed rock mass, the shear stress is borne by both the joint and the rock bridge, and the stress of the joint part is higher than that of the rock bridge.

Key words: discontinuous jointed rock mass, joint roughness coefficient, fractal model, rock bridge, failure mode