Results of pull tests of rock bolts and cable bolts in Sydney sandstone and shale

This paper discusses the result of 181 pull tests of rock bolts and cable bolts in the sandstones and shales of the Sydney region. The pull tests were carried out as part of the Sydney Metro Northwest tunnelling project. The tested bolts include: end-anchored corrosion-protected steel bolts, resin-grouted fibre reinforced plastic bolts, cement-grouted multi-strand cable bolts and friction bolts. Recorded and corrected bolt stiffness characteristics are presented by bolt type, grouting agent, lithology, bolt bar material and borehole diameter. Rock-grout and grout-bar interface bond strengths are assessed for different rock mass units and bolt parameters. Common problems with typical pull test arrangements and their impact on the resulting data are discussed. Examples of issues encountered during bolt installation, such as partial grout encapsulation and insufficient mixing of resin, are presented. Recommendations are made on how some of these problems can be detected and prevented.