Experimental investigation on mechanical properties and deformation mechanism of soft-hard interbedded rock-like material based on digital image correlation

The soft-hard interbedded rocks are often encountered in rock engineering such as mining engineering, tunnel engineering, and natural gas engineering. In this study, the horizontal soft-hard interbedded composite rock-like material (HSHC) specimens were prepared with different thickness ratios of rock-like layers, and a series of uniaxial compression tests were performed by using a self-designed loading mold. A parameter R was defined for the HSHC specimens, which is related to the thickness ratio of the soft and hard rock-like layers, the length-width ratio, and the mechanical parameters of the soft and hard rock-like materials. R was regarded to characterize the strength properties of the HSHC specimens. The test results showed that the axial strength of the HSHC specimens decreases first and then tends to be constant with increasing of R. Digital image correlation (DIC) technique was used to investigate the strain evolution and crack propagation process of the HSHC specimens. The displacement variation trend of the specimen can be roughly divided into three stages: stable deformation stage, rapid crack growth stage and instability failure stage. The failure mode of the HSHC specimens was mainly splitting tensile failure along the bedding plane. Meanwhile, a simplified mechanical model of laminated rock mass under uniaxial compression is established. The strength variation trend predicted by this model is consistent with the experimental results. The present study can reveal the failure mechanism of soft-hard interbedded rock mass at the bottom of the tunnel under the action of large horizontal stress after excavation.