Micro-cracking morphology and dynamic fracturing mechanism of natural brittle sandstone containing layer structure under compression

The failure and instability of sedimentary rocks are related to internal weak surface and potential damage. To explore the influence of layer structure on the crack expansion law and deformation characteristics of sandstone, this study investigated the effect of layer structure on apparent crack degree, microscopic damage law, acoustic emission and deformation field under uniaxial compression. The fracture modes include tensile fracture Ⅰ, tensile fracture Ⅱ, shear fracture and composite fracture with an anisotropic characteristics. The apparent crack degree and stress show a simultaneous evolution feature and the sandstone with significant layer deterioration effect have greater damage degree. The peak stress and elastic modulus have nonlinear exponential relation with layer angles. The acoustic emission (AE) behavior has a phased response to the aging fracture, and AE energy warning points and AE b-value dropping abruptly generally occur near the continuous stress drops or peak stress. The deformation field reveals the principal strain and resultant displacement has a spatiotemporal response characteristic and there is a typical damage competition relationship in the deformation concentration area. The fracturing effect intensifies the dissimilation behavior of deformation field, formation of strain concentration zone and banded dissimilation zones indicate the cracks penetration. The displacement field at the fracture tip shows a significant suddenness and strain concentration region is often pregnant with high-level displacement. These findings on the dynamic fracture mechanism are helpful in the deterioration characteristics of sedimentary rock in underground space engineering.