Published in the March 2008 Coal USA Magazine
The Hilti OneStep Bolt combines the drill bit head, drill steel, bolt and adhesive resin in a single unit. The two-component adhesive resin system is contained in a tubular cartridge. This resin cartridge is located in a steel inner tube enclosed in a second 4mm gauge steel tube. The bolt’s design ensures the resin cartridge is completely protected and will not damage or leak.
To use the bolt, a dispenser is fitted to the drill motor on the bolting rig and the OneStep Bolt is inserted and the drilling operation commences. Drill fragments-fines are flushed out by the flow of water through the annular gap between the bolt and the drill hole. The flushing water is fed to the bolt through the gap between the inner and outer tubes.
After reaching the intended drilling depth, dispensing is begun, encapsulating the bolt with mixed resin.
The OneStep bolt has been reviewed by Mine Safety and Health Administration (MSHA) and is undergoing different district approvals. The tests being carried out at mines throughout the country include drill, pull and functionality testing. Hilti's US division initially opened an operation service center in Grand Junction, Colorado last year to support the commercial introduction of the Onestep Rock Bolt. They continue to build the organization to support the Onestep establishment.
Hilti North America senior director Blake Griffin told American Longwall Magazine that he expected the same productivity gains in the US as those achieved in Germany and more recently Australia and New Zealand.
Trials last year at Australian and New Zealand mines, Broadmeadow, Spring Creek, Mannering and Angus Place, have helped prove the new bolt in Australian conditions in the hope it will help roadway development crews make a much-needed step change in development rates.
The Hilti “OneStep” Self Drilling Bolt was first introduced into the Deutsche Steinkohle (DSK) coal mines in Germany in 2004-05. The aim was to achieve quicker, stable and consistent bolt cycle times. The results were increased development rates with areas achieving 50-100% improvement, the quality of bolting standards improving and overall bolting safety standards increasing dramatically.
According to Hilti, the productivity gains using the OneStep can be measured in two ways. Firstly, faster bolt installation and improved bolt installation processes lead to a reduction in bolt cycle time.
“Special test results obtained from mines using the OneStep suggest that there is a high probability that primary ground support densities can be reduced as well as secondary support requirements. Improved strata reinforcement capability derived from the quality of resin mixing and encapsulation results in the total utilisation of the bolt length installed,” Hilti Australia mining sales and marketing manager Andrew Worth said.
“By completely bonding the roof bolt the load generation in the bolt will be higher and will be applied to a greater proportion of the roof strata.”
Eliminating many of the installation processes and improving face management by being able to quickly and safely place bolts where the roof is unstable are also major benefits for the bolt.
