Crack Initiation and Failure Mechanism of Granite with Single Crack

Damage identification and localization of cracked rock in underground tunnel and slope engineering is the widely and important research topic. Stress, strain and acoustic emission sensors installed on the pre-cracked real rock samples are used to reveal the crack initiation behavior and fracture mechanism under the uniaxial compression. The uniaxial compression strength (i.e., UCS) of the pre-cracked rock sample is obviously lower than that of the intact sample, and the average UCS is the lowest when the pre-crack angle is 75°. During the loading process, two typical failure modes of continuous fracture and periodical fracture for the pre-cracked specimens are reflected by the AE counts, and the initiation stress of specimens is obtained from the sudden increase of AE counts. Two types of newborn cracks are observed through the images: wing cracks induced by tensile stress and anti-wing cracks induced by compression-shear stress. Both types of cracks initiate from the tips of the pre-cracks, the initial crack angle in granite range among 0°–87°, and the larger the pre-crack angle is, the larger the initial crack angle is. The damage property and initiation behavior of the real cracked rock guide the protective engineering design for the fractured rock mass.