Effect of load control mode on the post-peak behaviour of siltstone

The mechanical properties and post-peak behaviour of rocks are typically determined using axial and circumferential strain control load methods. However, the effects of the load control mode on the mechanical properties and post-peak behaviour of rocks have not been investigated comprehensively. In this study, the mechanical properties and post-peak behaviour of siltstone are investigated using both the axial and circumferential strain control modes. Rock specimens are tested under uniaxial and triaxial compression. Laboratory test results indicate that the compressive strength, residual strength, and fracture angle are smaller when loading is performed via the circumferential strain control mode; however, the elastic modulus is higher. The stress–strain curves obtained from the axial strain control test are those of class I. However, the stress–strain curves obtained from the circumferential strain control test transited from that of class II to class I as the confining pressure increases. The occurrence mechanism of the class II curve and the transition of the stress–strain curve from class II to class I are clarified. The brittleness estimated from the rock specimens under the two load control modes indicate greater brittleness under circumferential strain control loading.