INNOVATION

“At all times we were asking ourselves - Can we do it safer? Can we do it better? Can we do it quicker?”

The installation of a 138m, 1200mm diameter string of HDPE pipe into the diversion culvert under the dam embankment as part of the temporary works river diversion strategy was a challenge. The team built a special attachment to connect the D9 bulldozer to the end of the HDPE pipe string to guide it up the 160m culvert under the dam.

“We managed to push it with the D9 to within 90mm of where it needed to be. We had to be quite precise because if we pushed it too far it would bump into other pipework that was already in the chamber, potentially damaging it.”

Lifting the HDPE pipe required the use of roller slings. However, the cost of buying them as a manufactured item and the long lead times to get the slings from Australia meant that another solution was required. The team designed their own slings and had them tested and certified to carry the required weights.

Using wire ropes, the team developed temporary debris booms to catch and move debris within the reservoir when there was a flood. This meant that when the flood waters receded the debris landed in the right spot. Forestry wire ropes were used with a pulley system to guide the floating boom up and down the reservoir.

Rock anchor drilling on steep slopes required the use of forestry tethering equipment which enabled the 21-tonne rock anchor drill rig to sit on the slope and be operated safely. Rock anchor drill depths drilled by the Epiroc T45 drill rig were designed in the office and drilled to the correct angle and inclination via GPS guidance in the drill rig.

Another example of GPS guidance was when the team mounted GPS mapping equipment onto the roller they used to compact the fill in the dam. This allowed them to generate a 3D model of the whole embankment, layer by layer, and to provide a construction “as-built” to the client. Precision drill and blast was required on several occasions to ensure that construction blasting didn’t damage the concrete structures already in place. Each blast had to be accurately designed, including the shape of the blast pattern and the delay sequence, and the predicted vibrations forecasted. Vibration monitors were used in real time to ensure they didn’t exceed the required specification limits.

The team purchased a diamond-tipped concrete saw that fitted onto the end of an excavator. As the rock was so brittle it was important to limit overbreak for the trenches for the spillway underdrains. Overbreaks require additional concrete work to be reinstated, so reducing overbreaks is a significant cost saving. A saw was purchased from Australia and the team learned the specialist skills to use it. GPS equipment was unable to be used to lay the pavement on the crest of the dam because of the hills blocking satellite visibility at certain times of the day. The team devised a way to use a Total Station to achieve precision control of the machine to do the prep work on the dam crest, which achieved level control to a millimetre accuracy.

For the dam crest pavement lay, the team made a special wing for the side of the plate compactor to enable them to pack a wedge shape into the aggregate as it was placed. This formed the required wedge for bitumen sealant between the parapet wall units on the crest.

3,000

Waterstop welded m

900,000

Earthworks Excavation m3

550,000 m3

Earthworks Filling (equivalent to two Wellington Stadiums)