Quantitative Identification of Cracks in Jointed Layered Rock Specimens under Uniaxial Compression

Few researchers have looked at the mechanical characteristics of rocks that are composed of numerous layers of various kinds of rock. Most strata in practical engineering are composite strata, and fracture propagation is frequently to blame for engineering mishaps. The digital image correlation method (DIC) and acoustic emission (AE) equipment were used to observe the crack strike and strain field changes of specimens that resemble rocks with a constructed joint under uniaxial compression in order to study the crack growth process and failure mode in composite rock strata under uniaxial compression. The research focus of this paper is to conduct a quantitative and qualitative analysis of crack types based on the data obtained from the DIC test. The covariance matrix was introduced to quantify the strain field dispersion of samples with joint dip angles α = 0°, 15°, 30°, 45°, 60°, and 75°. The outcomes of the analysis were as follows: the displacement data of the two crack sides were quantified using the novel method, and the crack types were determined to be tensile crack (type I), shear crack (type II), and composite tension–shear crack (type I–II); the covariance matrix-based parameter V can be used to describe the crack creation and spread process; and according to the growth rate of V , the crack types were identified as tensile crack (0.12 × 10 −4 –0.49 × 10 −4 ), shear crack (1.17 × 10 −4 –4.5 × 10 −4 ), and composite tension–shear crack (0.72 × 10 −4 –0.99 × 10 −4 ).