A new long-life, cost-saving mine roof bolt has been developed by Sydney-based Strata Control Systems. Tested at the Olympic Dam, Elura, Kanowna Belle and Rosebery mines, and Homebush Bay rail and M5 roadwork projects, the CT Bolt is described by SCS as a combination mechanical/grouted bolting system that provides immediate reinforcement via a mechanical point anchor and long-term reinforcement by grouting.
“The CT Bolt has been accepted for projects requiring a service life of up to 100 years, even in aggressive ground conditions,” the company said.
The bolt’s design features a plastic sleeve that insulates it against corrosive elements. A hollow, bulb-shaped dome ball welded to a short steel sleeve, in turn fitted to a dimpled, polyethylene tube, fits longitudinally over the bolt. Grout is injected through an opening in the dome ball and flows through an annular space between the tube and bolt. At the end of the tube, continued injection pressure causes grout to flow back between the tube and rock to the dome plate, providing a solid, full-column grouted fixture.
According to SCS, the chemically-inert polyethylene tube, which effectively covers the entire length of the high-tensile steel bar, protects the bolt from contact with aggressive elements that may penetrate air pockets or cracks in the grout and parent rock as a result of either poor installation or ground movement. Further ensuring the bolt’s long-term protection, the polyethylene tube has a 200% elongation capability said to accommodate areas subject to large ground movements that sometimes subject the fixture to high tensile or shear load.
The CT Bolt is fitted with a mechanical expansion shell point-anchor assembly to provide immediate support upon installation. Tension is applied in the usual manner, by mechanically tightening the nut fitted to the exposed end of the bolt.
The outer radial dimension of the complete CT Bolt assembly is designed to fit boreholes drilled by a standard 45mm blast-hole bit. According to SCS, use of standard blast-hole drilling equipment and consumables enables significant cost savings during bolt installation.
