Published in American Longwall Magazine

Conventional resin grouted passive anchors require multiple steps before the resin can be activated. The hole is first drilled, then the drill is retracted, followed by insertion of the adhesive cartridge. The anchor is then inserted and set.

In contrast, Hilti’s OneStep is drilled straight into the roof and the adhesive injected immediately with a 10-20 second curing time, depending on rock temperature.

The adhesive is embedded in the body of the anchor in a steel inner tube to protect against leakage during transport and storage.

Getting the adhesive to mix correctly has been the major obstacle for bolt manufacturers in the past in producing a commercially viable self-drilling bolt. Hilti claimed to have overcome this problem with the use of an axially shifting mixer at the point of release which provides correct mixing of the adhesive.

Test results indicated the design of the anchor offered consistency in installation. Because it is self-drilling, the anchor is always installed to the exact hole depth, with the optimum annular gap and adhesive volume. Gloving is also eliminated.

Materials management is substantially easier as one item replaces the four standard items used with other anchors.

The Hilti anchor is rated at less than 320 kilonewtons (ultimate load).

The company said the largest contribution of the OneStep anchor would be a 25-40% decrease in roadway development (geology dependent) through a reduction in the number of steps required to install a roof bolt.

Hilti has also developed a drill chuck adaptor which allows the anchor to be installed by any drill rig on the market.

OneStep has MSHA approval and is currently available to the US market.