A New Approach to Design of Ground Anchors in Rock with Due Consideration of Swelling Effects

It was found that the bond strength of ground anchors in weak Bringelly Shale was reduced resulting from the swelling effects during the drilling, clearing and washing process prior to grouting. This paper has proposed an approach on how the potential radial plastic displacement can be evaluated using an available empirical solution, and the swelling effect by means of numerical modelling during the ground installation process. It was found that the grout and rock interface is heavily influenced by the potential plastic displacement due to swelling. The conventional relationship of the ultimate bond strength of shale rock and the unconfined compression strength (UCS) has been reviewed for non-swelling rocks. A correlation relationship of bond strength equal to 0.11UCS when UCS <= 4 MPa and 0.14ULS for UCS > 4 MPa has been recommended for Bringelly Shale after the field pull-out testing and acceptance testing of many anchors in Bringelly Shale on the Sydney Metro—Western Sydney Airport, Station Boxes and Tunnelling project (WSA-SBT). This correlation could be used to forecast ground anchors in Bringelly Shale with swelling potential in the future.