Uniaxial experimental study of the acoustic emission and deformation behavior of composite rock based on 3D digital image correlation (DIC)

In this paper, uniaxial compression tests were carried out on a series of composite rock specimens with different dip angles, which were made from two types of rock-like material with different strength. The acoustic emission technique was used to monitor the acoustic signal characteristics of composite rock specimens during the entire loading process. At the same time, an optical non-contact 3D digital image correlation technique was used to study the evolution of axial strain field and the maximal strain field before and after the peak strength at different stress levels during the loading process. The effect of bedding plane inclination on the deformation and strength during uniaxial loading was analyzed. The methods of solving the elastic constants of hard and weak rock were described. The damage evolution process, deformation and failure mechanism, and failure mode during uniaxial loading were fully determined. The experimental results show that the \(\theta = 0{^{\circ }}\)–\(45{^{\circ }}\) specimens had obvious plastic deformation during loading, and the brittleness of the \(\theta = 60{^{\circ }}\)–\(90{^{\circ }}\) specimens gradually increased during the loading process. When the anisotropic angle \(\theta \) increased from \(0{^{\circ }}\) to \(90{^{\circ }}\), the peak strength, peak strain, and apparent elastic modulus all decreased initially and then increased. The failure mode of the composite rock specimen during uniaxial loading can be divided into three categories: tensile fracture across the discontinuities (\(\theta = 0{^{\circ }}\)–\(30{^{\circ }})\), sliding failure along the discontinuities (\(\theta = 45{^{\circ }}\)–\(75{^{\circ }})\), and tensile-split along the discontinuities (\(\theta = 90{^{\circ }})\). The axial strain of the weak and hard rock layers in the composite rock specimen during the loading process was significantly different from that of the \(\theta = 0{^{\circ }}\)–\(45{^{\circ }}\) specimens and was almost the same as that of the \(\theta = 60{^{\circ }}\)–\(90{^{\circ }}\) specimens. As for the strain localization highlighted in the maximum principal strain field, the \(\theta = 0{^{\circ }}\)–\(30{^{\circ }}\) specimens appeared in the rock matrix approximately parallel to the loading direction, while in the \(\theta = 45{^{\circ }}\)–\(90{^{\circ }}\) specimens it appeared at the hard and weak rock layer interface.