Experimental study on the relationship between local deformation and macro-crack evolution of granite under conventional triaxial compression

Abstract

Brittle failure of rock is characterized by the initiation, propagation and coalescence of micro- and macro-cracks. To study the macro-crack evolution of rocks, a parallel long strain gauge measurement apparatus was developed, which was composed of multiple long axial strain gauges and linear variable differential transformers (LVDTs). Using the developed strain measurement apparatus, conventional triaxial compression (CTC) tests were carried out on Linghai granite specimens. The results showed that a) using the radial strain of rock specimens monitored by LVDT as the servo feedback signal, the strain gauges can obtain the local complete stress–strain curves of the specimen. b) Macro-cracks often formed in the areas with large pre-peak axial strain (ε₁) values, but not in the areas with small pre-peak ε₁ values. c) There were three typical cracking patterns in Linghai granite: rapid tensile cracking, slow tensile cracking, and rapid shear cracking, among which rapid tensile cracking was the most common. d) The macro-crack evolution process can be deduced through the fracture sequence of the strain gauges and the failure pattern of the specimen. In addition, the typical crack propagation velocity of Linghai granite under a confining pressure of 80 MPa was approximately 667 m/s.

Keywords:

• Strain gauges
• brittle failure
• local strain
• macro-crack evolution
• crack propagation velocity

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors would like to acknowledge the support from the National Key R&D Program of China under Grant No. 2018YFC0407006, the fundamental research funds for the central universities under Grant No. N2101035 and Xiling deep shaft project supported by Deep Mining Laboratory of Shandong Gold Group Co., Ltd.