Ellerslie Highway Pier

The widening of SH1 required that the existing western pier to the Main Highway Overbridge be demolished to provide the necessary land area. A new pier would be constructed to provide the necessary support and this included a requirement for seismic ground anchors.

Grouting Services was awarded the subcontract for the supply and installation of the seismic ground anchors within the confines of the site located between the main trunk railway line and the main state highway. Limited headroom required the use of a specialist low height rig (Comacchio MC400P) and the holes were put down using a conventional down hole hammer. The ground encountered included fractured and voidy basalt which necessitated the need for grouting and re-drilling to stabilise the ground. A grout sock was also utlised to ensure the grout-ground bond was not compromised. The seismic ground anchors were fabricated to provide a 100year design life, and, the tendons comprised 17No x 12.7mm superstrands. The anchor lengths ranged from 13m to 15m. All anchors were tested and a provision was incorporated to provide for future stressing.