Your single point of reference for all your Geotechnical Inquiries
THE 25MM GARFORD BULB ANCHOR FOR CABLE BOLT REINFORCEMENT PART 1: LABORATORY RESULTS (1994)
The Garford bulb anchor is a modified cable geometry developed and patented by Garford Pty of Australia, and which has recently become widely available in Canada. It is produced by simply deforming the 7 wires (including the central kingwire) of a standard cable into a bulb1 (see Figure 1). Laboratory cable pull tests indicate that the bond capacity of the 25mm 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 water:cement ratio grout, which corresponds to operational conditions of low quality rock (ie: 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. For tests conducted at a 0.4 w:c ratio grout the dominant failure mechanism involved rupture of the strand (tensile strength of the strand = 250kN) and as such the capacity of Garford Bulb Anchor was independent of the effective rock mass confinement. Field test results will be presented in a companion paper.
Submitted to the CIM Bulletin MAY 1994
Department of Mining Engineering, Queen's University Kingston, Ontario.