Experimental Investigations of the Rock Brittleness Evaluation Under Different Loading Conditions

As a significant mechanical property of rock, brittleness is an important parameter that characterizes the mechanical behavior and damage characteristics of rock, such as rockburst risk, rock drillability, and friability. Based on the characteristic stress–strain threshold, energy evolution, and damage development of the pre-peak and post-peak stages of the rock, this paper proposed three brittleness evaluation indices to describe the entire process of deformation and failure. Uniaxial, triaxial, and cyclic compression loading tests with different lithology rocks were conducted to evaluate the new indices, which showed effective consistency with the failure modes. The results indicate a logarithmic growth relationship between the brittleness index and the uniaxial compressive strength and an exponential decrease in relationship with increasing confining pressure. The brittleness evaluation scale was established to achieve different lithology classifications, while the sensitivity analyses of confining pressure and lithology on rock brittleness were analyzed, the results distinguish the brittleness differences among various lithologies and highlight the importance of post-peak softening stage in brittleness analysis. Furthermore, for layered rocks, the brittleness exhibits significant anisotropy with increasing bedding angle, characterized by a U-shaped trend, initially decreasing and then increasing. The new brittleness indices contribute to the enhancement and refinement of the rock brittleness evaluation system.