A laboratory evaluation of the 25 mm Garford bulb anchor for cable bolt reinforcement

CIM Bulletin, Vol. 88, No. 992, 1995

A.J. Hyett and W.F. Bawden, Department of Mining Engineering, Queen's University, Kingston, Ontario N. Hedrick, Garford Pty. Ltd., Landsdale, Western Australia J. Blackall, Camada Technology International Pty Ltd., Balmain, N.S.W., Australia

The Garford bulb anchor is a modified cable geometry developed and patented by Garford Pty Ltd. of Australia, and which has recently become widely available in Canada. It is produced by deforming the seven wires (including the central kingwire) of a standard cable into a bulb* (Fig. 1). Laboratory cable pull tests indicate that the bond capacity of the 25 mm Garford bulb anchor is comparable to the nutcase cable, in excess of the birdcage cable, and significantly higher than standard 7-wire strand. Its comparative advantage over the latter is most significant for tests at low radial confinement and high watercement ratio grout, which corresponds to operational conditions of low quality rock (i.e. weak, highly fractured rock masses, foliated hanging walls, failed ground, etc.) and poor installation quality control (perhaps the most common explanation for cable bolt failures). It is under such conditions that cable bolting is often ineffective. The most impressive result is that for a reduction of the effective rock mass modulus by a factor of five, the Garford bulb cable capacity remains virtually unchanged.