Strength characteristics of rock anchored by NPR bolt with different preloads

This study compares the strength characteristics of rocks anchored by NPR bolts and ordinary bolts with varied preloads, based on the mechanical properties of NPR bolts (with a negative Poisson’s ratio). The results show that the uniaxial compressive stress-strain curve of ordinary anchored rocks exhibits noticeable abrupt changes. After reaching peak strength, the bolt breaks, whereas the stress-strain curve of NPR-anchored rocks is smoother. The NPR bolt enters the stage of continuous resistance after reaching maximal strength and does not break. As the preload increases, the strength of the anchored rock grows linearly. A calculation equation for the strength of the anchored rock is proposed based on the preload. The theoretical equation fits the test results well, and the fitted parameters show that NPR bolts can better increase the strength of the rock. The concept of dynamic toughness U C of anchored rock is proposed to reflect the comprehensive mechanical properties of anchored rock, including strength and plasticity. As the preload increases, the U C of ordinary anchored rock first decreases and then increases, while the U C of the NPR anchored rock does not change significantly with the preload when the strain is small, and the U C increases with the increase of the preload when the strain is large.