Experimental Study on Failure Characteristics of Schist Under Unloading Condition

The mechanical properties of rock under unloading condition have significant differences with those under conventional loading condition. To investigate the failure characteristics of schist under complex stress state, uniaxial and trixial compression and unloading confining pressure tests have been carried out on samples in the paper. The results show that the rock samples failed in coupling mode of shear and tension under uniaxial compression, and failed in shear mode under conventional trixial compression. However, the failure modes of the samples can be classified as shear, multiple fracturing, and multiple extension, and the strength of schist is closely related with the failure mode under unloading confining condition. For the unloading condition, the peak strengths of schist samples with shear failure mode are close to those under conventional trixial compression, but the peak strengths with multiple fracturing or multiple extension mode are much higher than those under trixial compression. The internal structure characteristics and stress paths were found to have major influences on the failure modes of schist. Therefore, the failure modes must be considered when the strength characteristics of schist are investigated.