Dam-Concrete

Project Info

Client: Waimea Water Ltd

Designer: Damwatch

Project Description

The Waimea Community Dam is a concrete-faced, rock-filled dam being constructed in the Lee Valley, near Nelson. It is one of the region’s most important infrastructure projects and the largest dam built in New Zealand in more than 20 years. Taylors Contracting is in a joint venture partnership with Fulton Hogan as contractors to Waimea Water Ltd.

Waimea Community Dam will:

  • Secure the region’s water supply for the next 100 years.
  • Improve water quality to provide a better environment for people, plants, fish, and animals.
  • Strengthen the economy through the success of primary industries and the subsequent growth of associated secondary and tertiary industries.
  • Provide an estimated economic benefit to the Tasman region of $600-900m in the first 25 years.
  • Taylors Contracting Waimea Community Dam Earthworks Manager Alex Smith discusses key project challenges and achievements during the past year.

Key achievements (June 2022 – June 2023):

One of the big challenges for everyone working on the project was that the last big dam in the country was the Clyde Dam in the 1980s and 1990s. Most of the contractor staff working on the Waimea Community Dam have had to innovate and problem-solve without having worked on a dam project like this before.

The project has encountered a number of unexpected factors, such as the rock geology conditions on the site (i.e. the hardness and softness of the rock) and the relative slope stability. This resulted in an embankment design with different types of fill materials and fill zones that the earthworks team had to deal with.

“We thought it was going to be a lot harder to excavate, but the soft rock created its own challenges with slope stability and worker safety. A lot more temporary works were needed for worker protection because of the geology we found.

“We have very strict specifications to build the dam to. Managing fill placement and bulk cut operations has been much more tricky than usual. You only have one chance to do it right. You’ve got lots of things you’ve got to keep juggling. We‘re focused on doing things safely and efficiently, making sure we’re getting all our documentation and communications in writing and trying to look forward for construction planning and problem solving. It makes the work days go quickly!”

At the peak of the project, Taylors had a team of approximately 25 working onsite and was running an impressive array of equipment, some of which was purchased specifically for the project.

“At peak time we were running up to seven dump trucks. We bought a 90-tonne excavator to work here, we had a 50-tonne excavator, and five or six other-sized 30-tonne to 20-tonne diggers. We bought a new drill rig for this project and had three bulldozers working onsite at one point.”

After nearly 20 years in the construction industry, it has been a real thrill for Alex to be involved in this project and he’s keen to work on large infrastructure projects in the future.

By the end of May 2024 the permanent works for the discharge pipework to discharge water from the dam down the Lee River will be completed. Once Taylors finishes dam construction, Alex anticipates Taylors will continue to work with adjacent landowners, building and maintaining private forestry roads in the valley.

How will the dam work once the project is completed?

“When the reservoir fills up and is full for most of the year it will flow over the spillway,” says Alex. “Water will come over the spillway/flip bucket and run off down the river. During the winter period the reservoir will hold water, so it fills up for later use.

In the summer when people start irrigating down on the plains or if there’s a drought the intakes will become active and they’ll start drawing the reservoir down maintaining the river flows.

“The water will go through the intakes into a pipe which runs through the concrete conduit under the dam embankment. The pipe will discharge into the river so the community can use the volume of water in the summer period and avoid restrictions on irrigation during drought conditions and continue irrigating on the plains.

“People using the river for swimming and other recreational activities won’t notice any difference, in fact there will be more flow in the river which will make the swimming spots better.”

Waimea Community Dam Joint Venture Key Personnel:

John Roche
Current Project Director
Fulton Hogan Taylors Joint Venture

Matt Taylor
Construction Manager
Fulton Hogan Taylors Joint Venture

Alex Smith
Earthworks Manager
Fulton Hogan Taylors Joint Venture

Project highlights:

  • Bulk Cut operations during the embankment cut-to-fill operation.
  • Parapet wall installations across the crest of the dam
  • 76 units, each unit weighing 21 tonne, had to be placed with a 120-tonne crawler crane to an accuracy of +/- 12mm. Units had to be placed and keyed together. Taylors controlled the works and did the base prep work, which had to be accurate within a millimetre so that the 4.4m high units sat correctly.
  • Crest backfill: The way in which filter zones come together at the crest of the dam and interlocked together required a precise building sequence and placing fill within a confined working space at the top of the dam.

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.

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