Experimental Study on Mechanical Properties Optimization of Anchored Rock Mass Samples with Various Fissure Angles by NPR Steel under Uniaxial Compression

Rock formations naturally contain numerous joint fissures that can impact their mechanical properties and damage mechanisms. Among the commonly used materials for supporting, micronegative Poisson’s ratio (NPR) steel has become a new type of supporting material due to its high strength, high toughness, super energy absorption, and other mechanical properties. Experiments in this article studied the affection of fissure angles and various anchored environments on the mechanical performance of samples. Rock mass samples anchored with ordinary Q235 steel (Q235 group) and unanchored rock mass samples were used as control groups. The two groups were then compared and analyzed in terms of their stress–strength curves, fissure angle characteristics, and anchoring strength. The conclusion indicates that the fissure resistance and mechanical properties of fissured rock mass samples are significantly improved under the anchoring effect of NPR steel. With the uniaxial load, the anchored rock mass sample increases the anchorage reinforcement stage compared to the unanchored rock mass group. At the same fissure angle, the average elastic modulus of the NPR steel–anchored rock mass sample group (NPR group) is 23.85% higher than that of the Q235 group, while the average peak stress is 23.55% higher than the same group, which proves that the compressive recovery ability of the NPR group is superior to the Q235 group. In addition, fissure angle affects the mechanical properties of rock masses. At the equal anchoring environment, the peak strength of the rock mass sample shows a concave trend when the fissure angle keeps increasing. When the fissure angle α = 45°, the peak strength of groups reaches 21.829, 26.443 (Q235 group), and 29.532 MPa (NPR group); similarly, the elastic modulus reaches 3.97, 5.47 (Q235 group), and 6.87 GPa (NPR group), and both peak strength and elastic modulus attain their minimum values, explaining that the mechanical properties of the NPR group are optimal. The conclusions reflect the strengthening effect of the NPR material on fissured rock masses compared with ordinary materials, and the results have broad application significance for rock mass support engineering.