An experimental investigation of failure mechanical behavior in cylindrical granite specimens containing two non-coplanar open fissures under different confining pressures

Abstract

Fissures play a significant role in predicting the unstable failure of rock mass engineering. For deep rock underground engineering, rock mass containing pre-existing fissures is usually located in triaxial stress state. Therefore, not only pre-existing fissure but also confining pressure affects the failure mechanical behavior of rock material. In this research, the granite specimens containing two non-coplanar open fissures were investigated by a series of conventional triaxial compression tests. First, the effect of bridge angle and confining pressure on strength and deformation characteristics of granite specimens was evaluated. Results show that the triaxial compressive strength, failure axial strain, and crack damage threshold increased nonlinearly with confining pressure. Under high confining pressures, elastic modulus was insensitive to bridge angle. Then, an X-ray micro-CT scanning technique was used to analyze the internal fracture characteristics of granite specimens with respect to various bridge angles and confining pressures. Five typical crack coalescence modes were identified, namely, indirect coalescence, shear coalescence and three types of tensile coalescence. The reconstructed 3-D CT images indicated that under uniaxial or low confining pressures, the bridge angle had a significant effect on crack evolution behavior, while under high confining pressures, shear-dominated failures occurred with the development of anti-wing cracks.

Keywords

rock mechanics / granite / three-dimensional non-coplanar open fissures / X-ray micro-CT / triaxial compression

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