Crack Evolution and Failure Modes of Shale Containing a Pre-Existing Fissure under Compression

Lin Li; Yuehua Liu; Wei Liu; Xiong Zhang; Jie Chen; Deyi Jiang; Jinyang Fan

doi:10.1021/acsomega.1c03431

Crack Evolution and Failure Modes of Shale Containing a Pre-Existing Fissure under Compression

ACS Omega. 2021 Sep 20;6(39):25461-25475. doi: 10.1021/acsomega.1c03431. eCollection 2021 Oct 5.

Authors

Lin Li^{1

2}, Yuehua Liu^{1

2}, Wei Liu^{1

2}, Xiong Zhang^{1

2}, Jie Chen^{1

2}, Deyi Jiang^{1

2}, Jinyang Fan^{1

2}

Affiliations

¹ State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China.
² School of Resources and Safety engineering, Chongqing University, Chongqing 400044, China.

Abstract

To investigate the crack evolution of Longmaxi shales with a single prefabricated fissure, a CCD (charge coupled device) camera and AE (acoustic emission) monitoring equipment were employed. On the basis of real-time CCD photographs and AE events, a real-time crack evolution process in fissured shale specimens under uniaxial compression was investigated. The crack initiation angle and extension angle were calculated, the relationship between the crack initiation stress, strength, and crack angle was compared, and the proportion of tensile and shear cracks at different stages of the whole compression process was briefly analyzed. The results demonstrate that, with the increase in fissure angle (α), the weakening ability of the prefabricated fissure to uniaxial compressive strength and crack initiation stress was reduced. The initial cracks and secondary cracks always appeared at the tip of the pre-existing fissure in the form of tensile cracks for α = 30-90°. The crack initiation angle and expansion angle increased first and then decreased rapidly with α increasing. Furthermore, the ultimate failure modes were mixed tensile and shear failure when α = 0-90°. The crack evolution of the fissured shale was progressive, but the final failure of the fissured specimen occurred rapidly. Furthermore, the appearance of the cracks, stress drops, and AE counts had good consistency in time.