Experimental investigation on fracture coalescence behavior of red sandstone containing two unparallel fissures under uniaxial compression

Natural rock usually contains a lot of flaws, such as fissures, joints, weak surfaces and faults, which have a significant effect on the strength, deformability and crack coalescence behaviors of rock material [1–5]. In order to improve the understanding of fracture mechanism of rock engineering containing intermittent structures, a lot of experimental studies have been performed for all kinds of rock materials or rock-like materials containing two fissures [6–10]. Wong and Chau [6] investigated the crack propagation and coalescence on rock-like materials containing two inclined open or closed fissures, which obtained three main modes of crack coalescence in two fissured specimens under uniaxial compression. Feng et al. [7] carried out a number of experimental studies to explore the mechanism of multi-crack interaction in limestone specimens (the size of the specimen was 15 30 3 mm) with two fissures of different geometries under the coupled uniaxial compressive stress and chemical solutions with different ionic concentrations and pH values. Yang et al. [8] made uniaxial compression tests for cylindrical marble specimens with different pre-existing fissures, which analyzed the effect of fissure geometry on strength and deformation failure behaviors of brittle marble material. Wong and Einstein [9] summarized the effects of the flaw angle, ligament angle and length on the cracking processes and coalescence patterns of Carrara marble specimens containing two open fissures and used a high speed camera to observe the specimens at a macroscopic scale. Yang [10] performed an experimental study on the influence of coplanar fissure angle on the strength, deformation