An experimental study on failure mechanical behavior and cracking mechanism of rectangular solid sandstone containing two non-coplanar fissures under conventional triaxial compression

Abstract

Fissures are generally existing in engineering rock mass, and cracking pattern observed in specimens with multiple fissures is analogous to the pattern obtained in specimens with two fissures, whereas the cracking coalescence of real rock specimen under triaxial compression have rarely been investigated. Therefore, thirty fissured rectangular specimens containing two non-coplanar fissures with different ligament angles were prepared to perform triaxial compression in this work, and the stress-strain curves, strength and deformation parameters, ultimate failure modes and Acoustic Emission (AE) characteristic were investigated. The experimental results indicate that pre-existing fissures have a significant effect on the stress-strain curves, more stress drops were observed before and after the peak strength, whereas confining pressure cannot reduce stress-drop. Cohesion (C) of peak strength and damage threshold has different trend with ligament angle (β), and the C of the peak strength is larger than that of the damage threshold. Pre-existing fissures have more effect on damage threshold than peak strength; cracks are easier to initiate in fissured specimen. It is easier to coalesce when ligament angle is parallel to the maximum principal stress, and cracks are easier to expand in width direction than that in thickness direction. The coalescence of the two non-coplanar fissures is classified as five typical modes, and the CT result shows that crack distribution in depth direction is similar. Crack classification by AE parameter and k-mean method can reflect the cracking process in a certain extent. It is more drastic when shear crack initiates, and tensile crack propagates in a stable way.