Performance assessment of grouted cable bolt system under rock strata movements using multi-axis testing

Cable bolt systems are extensively used to stabilize the roof of underground mining roadways from collapse due to the movement of unstable rock strata. These cable bolts are anchored at both ends and grouted. The inaccessible end of the cable bolt is typically anchored via a resin plug, whereas the exposed end comprises a steel plate with a barrel and wedge. Rock strata movements under gravity or tectonic activities can cause relative separation due to sagging and/or shear sliding of adjacent rock strata and lead to either axial loading or a combination of both axial and shear loading on the cable bolt system. Therefore, this paper presents an experimental study into the large-scale system-level performance of a cable bolt system under simulated relative rock strata movements including vertical separation and shear sliding. The tests were carried out using the Multi-Axis Substructure Testing facility at Swinburne University of Technology, Australia. High-strength reinforced concrete was selected for the confining medium to represent the strong rock strata, while the selected grout was a blended cementitious powder capable of developing high early-age strength and is among the most widely used by the mining industry. The tests were carried out within a 48-h window from grouting to study the influence of the grout medium on the overall system level performance and a non-anchored scenario has also been investigated to provide insight into the potential effects of damaged or unreliable end anchoring.