Abstract: In order to study the strength and crack coalescence behavior of sandstone containing two pre-exisiting non-coplanar fissures, a modified Rigid Body Spring Method is proposed to simulate the process of uniaxial compression tests, and a set of micro-parameters calibrated by uniaxial compression laboratory test results was used to set up a model of fissured rock samples containing two pre-exisiting non-coplanar fissures. On the basis of the simulated results, the influence of rock bridge inclination on crack initiation stress, peak strength, failure mode and crack coalescence behavior was investigated. Results show that crack initiation stress and peak strength both decreased in the presence of a rock bridge inclination smaller than 60°, and vice versa. According to the differences of the rock bridge inclination, the failure mode of specimens could be divided into three types: the penetration failure of single wing crack, the penetration failure of the coalescence of wing crack and the penetration failure of the coalescence between wing crack and prefabricated fissures. Rock bridge inclination has some impact on the failure degree of the rock bridge, and it is easy to coalesce for 60° rock bridge but hard for 0° and 120° rock bridge.

Key words: two pre-exisiting non-coplanar fissures in sandstone, crack propagation, anisotropy, rock bridge inclination, crack penetration, rigid body spring method