Investigation of mechanical behavior, AE and EMR characteristics of rocks under compression-shear loading via variable-angle shear tests

The surrounding rocks of underground engineering are usually subjected to the coupling of compressive and shear stresses. The mechanical characteristics of underground geomaterials subjected submitted to compression-shear loading have received considerable attention recently. The complex response arises from the microstructure redistribution under high in-situ stress and the resulting fracture behaviors at multiaxial stress states. Understanding the compression-shear behavior and failure mechanism of rocks is of essential importance for mechanical characterization and construction safety in deep underground engineering applications. In this study, variable-angle shear tests are conducted for cubic sandstone samples to investigate damage evolution under compression-shear loading, and the acoustic emission (AE) and electromagnetic radiation (EMR) are simultaneously monitored to record crack development. The mechanical behaviors of rock with AE and EMR responses in variable-angle shear tests with shear angle of 30°, 45° and 60° are analyzed. Then, correlation between AE and EMR is evaluated. Damage evolution of the rock specimen is described based on AE and EMR energy. Fractal dimension and b-value of AE and EMR time series are calculated to further reveal the microscopic crack mechanism of rocks. The results suggest that the continuous decline of fractal dimension and b-value of AE and EMR can act as the precursor of rock failure.