Shear fracture in sandstone under plane-strain compression

Experiments on Berea sandstone at 5 MPa confinement were conducted to investigate shear banding under plane-strain compression. Locations of acoustic emission showed propagation of a shear band during post-peak response. The eventual failure surface consisted of two distinct regions called primary and kinked fractures, with evidence of a process zone at the termination of the primary fracture. Features identified using thin-section microscopy suggested that the primary fracture was formed in shear while the kinks displayed mixed-mode qualities. A linear analysis of a closed crack demonstrated that part of the post-peak response could be explained as shear-crack growth, with Berea sandstone having a mode II fracture toughness of 3 MPa√m.