Overcoming the Challenges of Grouting Ultra-High Capacity Dam Anchors in Jointed Quarzitic Sandstone

The raising of Hazelmere Dam by an unprecedented 7 m required technology never before seen in the KwaZulu Natal region of South Africa. Extensive feasibility studies established that the optimum solution to facilitate the raising was to install 84 high capacity rock anchors through the concrete superstructure into the underlying rock. The anchors, installed in 355-mm boreholes, ranged in size from 49 to 91 strands (15.7-mm diameter) and were up to 90-m long. With test loads up to 19042 kN, these anchors equalled the largest ever installed on a post-tensioned dam. In order to quantify in situ rock/grout bond stresses, a comprehensive test anchor programme was commissioned and this involved the world’s largest sacrificial test anchors. The nature of the ground necessitated an extensive programme of pregrouting to ensure that the boreholes were sufficiently grout tight so that the primary load bearing anchor grout would retain its full integrity. The grouting of the corrosion protection system in anchors of this size called for innovative techniques to ensure successful execution and these aspects are also described in the paper which focuses primarily on the test anchor programme.