Layered rock bodies are widely distributed in the Earth’s crust and exhibit significant discontinuities and anisotropy, resulting in complex mechanical properties. To investigate the spatiotemporal evolution and deformation characteristics of layered composite rock failure, this study prepared soft–hard composite rock specimens with varying soft rock thickness proportions based on similarity theory. Uniaxial compression tests were conducted in conjunction with three-dimensional digital image correlation (3D-DIC) technology. The results indicate the following: A significant negative correlation exists between the soft rock thickness proportion and the mechanical properties of the composite rock. When the soft rock proportion increased from 10% to 90%, the peak strength and elastic modulus decreased by 63.4% and 36.8%, respectively. Axial strain of soft and hard rock decreased gradually with increasing soft rock proportion. Radial strains show significant differences: the hard rock radial strain initially increased and then decreased, whereas the soft rock radial strain consistently diminished, indicating that a higher proportion of soft rock had a more pronounced effect on its radial strain. Strain concentration zones first emerged in the soft rock, whereas deformation in the hard rock zones lagged. As the proportion of soft rock increased, the failure mode of the composite rock transitioned from being hard rock-dominated to soft rock-dominated mechanisms and displacement gradually decreasing from high to low across different locations. The quantitative relationship between surface strain recorded by DIC tests and the damage factor can effectively reflect the entire process of rock failure. The damage evolution equation established on this basis exhibits good agreement with experimental data, demonstrating its rationality.
Li et al. (Thu,) studied this question.