Experimental study on the mechanical characteristics of NPR anchored rock under kilometer-deep buried high geostress conditions

In this paper, a biaxial compression experimental study of NPR (Negative Poisson's Ratio) and PR (Poisson's Ratio) anchored rock under different burial depth conditions was conducted around a new type of constant resistance large deformation anchor cable, also known as NPR anchor cable. A comparative analysis was performed on mechanical characteristics of the two types of anchored rock. Furthermore, a concept of static toughness for anchored rock was established to evaluate the comprehensive mechanical performance. The results indicate that with increasing confining pressure, the elastic modulus of both types of anchored rock exhibits a gradual increase. The peak strength and residual strength initially decrease and then increase. The NPR anchored rock has higher elastic modulus, peak strength, and residual strength compared to PR, with increases of 17.5%, 26%, and 25%, respectively. As the confining pressure increases, the fine and short shear cracks within the lateral surfaces of the two types of anchored rock transform into wider and longer cracks. The final integrity of the NPR anchored rock is demonstrably superior to that of the PR. Compared to PR, the cumulative energy, cumulative count, and energy value per unit count of the NPR anchored rock throughout the experiment are significantly lower values. A calculated analysis revealed that the static toughness of the NPR anchored rock is considerably greater than that of PR.