5. Experimental Investigation on Fracture Coalescence Behavior of Red Sandstone Containing Two Unparallel Fissures

In nature, engineering rock masses do not always contain parallel fissures and are generally composed of unparallel fissures (Lajitai et al. in Rock Mech Rock Eng 27:89–111, 1994; Lee and Jeon in Int J Solids Struct 48(6):979–999, 2011). Lee and Jeon (Int J Solids Struct 48(6):979–999, 2011) carried out uniaxial compression experiment for Diastone (types of molded gypsum) and Hwangdeung granite containing two unparallel fissures (a horizontal fissure and an inclined fissure underneath). The results showed that crack initiation and propagation had similar and different patterns depending on the material. For Diastone and Hwangdeung granite, tensile cracks were observed followed by the initiation of shear cracks and coalescence occurred mainly through the tensile cracks or tensile and shear cracks. But up to now, no laboratory experiments have been carried out on red sandstone specimens containing two unparallel fissures with different fissure angles. Besides, in the previous investigation for rock specimens containing two unparallel fissures, AE monitoring technique had not been adopted and the relationship between macroscopic deformation and fracture coalescence process was not constructed.