Installation of permanent multistrand ground anchors with a helicopter and hollow bar anchors through the wing walls for seismic strengthening
Lake Waitaki is created by the Waitaki Dam, a 36m high spill weir dam built between 1928 and 1934. The Waitaki power station has an installed capacity of 105MW. Waitaki was the last dams built in New Zealand with excavation done with pick and shovel, not heavy machinery.
As part of a major upgrade to Meridian Energy's asset, the original wing walls of the spillway required strengthening. Geovert worked closely with the engineers at Damwatch during the development of the design on a restricted access construction a methodology to ensure the anchors were installed and tested to BS8081 standards.
The permanent 5No. 15.2mm strand ground anchors were installed vertically down through the old concrete wing walls and into the fractured foundation rock to a depth of 20m. The anchors were constructed to best practice standards each being predrilled and pregrouted with water testing completed to ensure the anchors were installed into a grout tight holes. The sheathed and greased ground anchors were lowered into position with a helicopter due to the limited access, each tested to 880kN and locked of to the DWL at 700kN.
Titan 40/16 duplex anchors were installed with grout flush horizontally through the wing walls to seismically strengthen the structure. Working through the middle of winter challenged the team with many days staying below zero to keep the air and grout lines from freezing and ensuring the integrity of the curing of the grout sampling and our grout testing procedures.
Lift off tests were successfully completed 12 months after the anchors were locked off to ensure there was no creep.