Shear performance of quasi-NPR steel bolted rock joints at different shear rates

Abstract

To study the shear performance of rock joints reinforced by NPR (negative Poisson's ratio) bolts, direct shear experiments with different shear rates were carried out on both quasi-NPR steel and conventional steel bolted rock joints, and DIC (digital image correlation) technique was applied to analyze the influence of bolting on the deformation of rock joints. The experiments show that (1) increasing shear rate weakens the deformation capacity of bolts before their failure and the transformation of loading from the bolt to the rock mass. A higher loading rate results in lower resistance strength of HRB bolts but has little effect for that of NPR bolts. (2) The shear performance of NPR bolts, including the bolt contribution, the deformation capacity and the transformation of load to the rock, is better than conventional bolts at both shear rates applied here, with obvious superiority at the higher shear rate. Through the analysis of reinforcement mechanisms, we suggest that the novel deformation characteristics of NPR bolts could explain their better shear performance. Finally, the deformation field obtained by the DIC technique shows a good correlation with the size of the compaction zone and could help quantitatively characterize the influence of bolting.