Experimental study on uniaxial mechanical properties of 1 G NPR anchor sandstone

The experiment investigates the stability of rock masses anchored with 1G NPR (Negative Poisson’s Ratio) anchor cables. Sandstone was selected as the test material, and 1G NPR anchor cables were designed and applied. Rock specimens were subjected to uniaxial compression and acoustic emission (AE) analysis under both lateral confined and unconfined conditions. The study compares three anchoring methods: unanchored, conventional cable-anchored, and 1G NPR cable-anchored. Experimental results show that the uniaxial compressive strength of rock specimens with 1G NPR anchor cables is at least 20% and 9% higher compared to unanchored and conventional cable-anchored specimens, respectively.Failure characteristic analysis reveals that unanchored specimens experience tensile failure, leading to a mixed mode of tension-shear failure, with a high degree of fragmentation after failure. In contrast, the 1G NPR cable-anchored specimens exhibit shear-dominated failure, with the rock mass in the anchoring zone remaining relatively intact, and a lower degree of fragmentation overall.AE analysis further demonstrates that the cumulative ring down count for the 1G NPR cable-anchored specimens is only one-third of that for the unanchored specimens. The cumulative ring down count curve for unanchored specimens shows a gradual increase in the early stages, followed by a sharp spike at failure. In comparison, the 1G NPR cable-anchored specimens exhibit a stepwise increase in AE activity during the early stages, without a sudden burst of activity at failure. The 1G NPR anchor cables significantly enhance the peak strength of the sandstone specimens. In the post-peak phase, the 1G NPR anchor cables release the accumulated energy of the anchored rock mass through multiple internal structural changes and delay the propagation and penetration of cracks, resulting in the minimized degree of fragmentation after failure.