Stress–strain and acoustic emission characteristics of cement-based materials used to simulate soft rock with fractures

Abstract

Instability failure in rock mass engineering is closely related to expansion of joint fissures. In this study, uniaxial compression tests and acoustic emission (AE) measurements were carried out simultaneously on specimens of soft rock-like material with different fracture angles and connectivity values to better understand their influence on the deformation and failure of the material. The stress–strain curve and AE signal of fractured soft rock-like material are similar to those of intact soft rock-like; specifically, they exhibit a compaction, elastic deformation, stable fracture development, and unstable fracture development. The main differences between fractured and intact material occur during post-peak failure stage. Under the combined influence of fracture angle and connectivity, the uniaxial compressive strength of fractured soft rock-like material ($f_{\mathit{cu}}^{{}^{\prime }}$) is lower than that of the intact soft rock-like material (f_cu), and can be described by the relationship $f_{\mathit{cu}}^{{}^{\prime }}=f_{\mathit{cu}}·\alpha$, where $\alpha$ is the strength reduction coefficient, fitted as $\alpha =0.8228+0.00411x-0.00789y$. In this equation, x is the fracture angle (${}^{\circ }$) and y is the fracture connectivity (%). Under uniaxial compression, the main types of secondary cracks were wing cracks and secondary coplanar cracks. The specimen with a fracture angle of 30° mainly underwent tensile failure under loading, whereas those with fracture angles of 45° and 60°mainly experienced shear failure under high-connectivity conditions (45%).