But since September 2005, an alliance consisting of Mighty River Power (the client), Italian foundation-engineering specialist Trevi and Brian Perry Civil has been conducting a unique precision drilling programme designed to cut off fissures in rock beneath the Arapuni Dam. When the dam was being built in 1927, engineers discovered seepage of water. Treatment was carried out from time to time, though the seepage did not pose a safety risk.
However, in 2000, subsoil monitoring showed a change in pattern and, as a result, a drilling rig was airlifted into the area, exploratory holes were drilled inside the dam galleries and interim grouting work was carried out.
Mighty River Power and design consultant Damwatch Services decided to minimise the risk of future seepage by the construction of cut-off walls across the fissures. The collaborative-option selection process with the contracting team determined that drilling a series of precise holes in the dam and underlying rock, then filling the fissures with concrete, would safely meet project objectives.
The dam would continue to produce electricity and operate normally while the programme was underway. This decision affected the number of potential construction options, and controls some of construction practices.
Trevi, a world leader in foundations engineering, was the selected contractor and an alliance was judged to be the best contracting method. Through its famous manufacturing subsidiary, Soilmec, Trevi as access to cutting-edge foundation-drilling machinery.