For decades cablebolts have been used to support stope boundaries, wide spans, drawpoints, crown pillars and other permanent excavations such as crib rooms and workshops. In recent years mechanised cablebolting machines have become more common. A mechanised installation requires the grout to be pumped into the borehole before the cable is inserted. There is no opportunity to plug the collar of the hole to avoid grout running out of the hole, as is done when manually installing cablebolts. To avoid this issue, a thicker grout is mixed which will remain up the hole while the cable is installed.
There are still some unknowns about what is the best water-cement ratio for achieving good quality cablebolts. The grout is required to be thin enough to fully encapsulate the cable, have sufficient bulb infill and show good grout qualities such as minimal air bubbles and cement lumps, however it must be thick enough to overcome the force of gravity and remain up the hole while the grout cures.
This research project conducted a series of tests using varying water-cement ratios and a number of different cable configurations in order to identify the best water cement ratio for cablebolting upholes in underground metalliferous mines. Mechanised cablebolting rigs were used to install the sample cablebolts in removable PVC pipes to allow the samples to be sliced sectionally so the encapsulation levels and grout properties could be studied in detail.
The results for this project were significantly poorer than expected mainly due to a number of experimental factors. No definite conclusions could be drawn based on the results obtained throughout the experiment. It was recommended that further research should be conducted using a modified testing regime. The main benefit of this research will be to educate operators on the effects of poor cablebolt installation techniques. Despite the poor results, this research project will still be of great use to the underground cablebolting industry in Australia.