Mechanical Characterisation of Modified Cable Bolts Under Axial Loading: An Extensive Parametric Study

A wide range of modified cable bolts are currently used for ground support in different conditions in Australian underground coal mining operations. This is mainly based on the belief that the performance of modified cable bolts is better than conventional cable bolts. Despite this positive view, very few studies have characterised the performance of modified cable bolts in service. A new laboratory-based pull-out testing facility was employed in this study to investigate the behaviour of two different types of modified cable bolts under axial loading including Garford twin strand bulbed and MW9P (smooth wire). The impact of different parameters including the compressive strength of the grout and the confining medium as well as borehole diameter on the performance of Garford twin strand bulbed cable bolt was investigated. In the case of the MW9P cable bolt, only the effects of borehole diameter and grout compressive strength were examined. A full factorial experimental programme was designed based on Taguchi method to explore the performance of these two cable bolts under different testing conditions. Consequently, an analysis of variance (ANOVA) was conducted to assess the weighting contribution of each parameter (e.g. borehole diameter, the compressive strength of grout and confining medium) to the load-displacement performance of Garford twin strand bulbed and MW9P cable bolts. For the Garford twin strand bulbed cable bolt, it was concluded that the compressive strength of the confining medium was the most influential parameter in the determination of the peak and residual loads as well as initial stiffness. It was also observed that an increase in the compressive strength of either the confining medium or the grout led to an increase in peak and residual loads in the Garford twin strand bulbed cable bolt, while borehole diameter had no sensible effect on peak and residual loads as well as initial stiffness. In the case of the MW9P cable bolt, the compressive strength of grout had the greatest impact on the peak and residual loads whereby, the peak and residual loads varied directly with grout compressive strength. A 10-mm increase in borehole diameter of MW9P cable bolt had negligible effect on the peak and residual loads as well as initial stiffness.