Failure Behavior for Rocklike Material with Cross Crack under Biaxial Compression

Abstract

This paper presents an experimental study in which molded gypsum specimens with different crack geometries (T-shaped and X-shaped cross crack) were tested in biaxial compression. Crack propagation and failure behaviors were investigated and nine crack types were detected, namely, wing crack, antiwing crack, secondary crack, horizontal wing crack, quasi-coplanar wing crack, quasi-coplanar secondary crack, far-field crack, surface spalling, and lateral split crack. Moreover, horizontal wing crack and quasi-coplanar wing crack were first observed in the rocklike specimens, which was caused by the added confining pressure. Besides, the cracks and failure modes under uniaxial and biaxial compression were compared according to proposed nine types of new cracks. With an increase in confining pressure, surface spalling and lateral split crack appeared. Lateral split cracks were observed only in T04 (σ2=1.5 MPa), X03 (σ2=1.0 MPa), and X04 (σ2=1.5 MPa), which indicate that lateral split crack is hardly induced under lower confining pressure. The reason is that confining pressure prevents the lateral deformation, therefore, failure can appear only along the free face such as surface spalling and lateral split crack. In practice, surface spalling is the common failure near excavation faces in deep tunnels, which validates the experimental results here.