Comparative study of shear performance of fully-grouted and energy-absorbing bolts under varying normal stress during cyclic shear tests

Abstract

Jointed rock masses are often subjected to complex cyclic shear loads, which may originate from factors such as earthquakes, mining activities, or traffic. Rock bolts are widely used to enhance the stability of jointed rock masses, and the mechanical behavior and failure characteristics of different types of rock bolts under shear conditions can significantly impact the shear resistance and overall stability of the rock structure. This study analyzed the cyclic shear performance of two types of rock bolts under varying normal stress conditions. The results showed that an increase in normal stress significantly enhanced the peak shear stress and shear resistance of the specimens by compacting the contact interface and increasing friction. However, at higher normal stresses, the contact interface between the rock bolt and the rock mass experienced greater stress concentration, which could lead to early bolt failure. Although fully-grouted rock bolts exhibited strong mechanical interlock and high initial shear strength, they were more prone to brittle fracture due to localized stress concentration, increasing the risk of instability. In contrast, energy-absorbing rock bolts, through mechanisms of plastic deformation and energy absorption, effectively alleviated shear stress concentration and demonstrated better toughness and ductility. As normal stress increased, energy-absorbing rock bolts, with enhanced friction and a larger range of shear displacement, absorbed energy more effectively, resulting in a significant increase in shear energy-far surpassing that of fully grouted bolts, which relied primarily on mechanical interlock. Additionally, with repeated loading cycles, the shear stiffness of energy-absorbing rock bolts showed more gradual and stable degradation compared to fully grouted bolts.