Mechanical performance of rock bolts under combined load conditions

Abstract

Rock bolts are subjected to different loading conditions along their lengths such as axial, bending, and/or shear forces, which can cause failure at lower loads than those considered for design purposes. The common existing methodologies do not consider the actual loading of the rock bolts and assume it is only pure axial or pure shear. This study was conducted to investigate the un-grouted rock bolt performance under combined load conditions. Two loading regimes were evaluated: the effect of initial shear displacement on axial load capacity and displacement, and the effect of axial displacement on the shear load capacity. The first regime was also conducted for shear with a gap, when there is a spacing between the shear interfaces. The results of this study showed that the rock bolt can resist higher axial loads than shear under pure or combined load conditions. Under combined load conditions, the rock bolt capacity decreased significantly for both regimes. However, when applying the shear load with a gap, the rock bolt load capacity was not affected significantly. Also, the total bar deformation was improved for shear and axial. The findings of this study show the need to improve the rock bolt design considering the complex loading conditions in situ with/without a gap. Keywords: Rock bolt, Combined load, Gap test, Failure mechanism, Axial load, Shear load