A Digitally Tailored Approach Fortifies Construction of New Zealand’s Waimea Community Dam

October 22, 2020

Customer Profile:The Waimea Community Dam will be New Zealand’s first large dam built in over 20 years. The $104.4M project is under construction by Fulton Hogan and Taylors Contracting Co. Ltd as part of the FHTJV joint venture on behalf of Waimea Water Ltd, a joint venture between Tasman District Council and Waimea Irrigators Ltd.

Business Challenge: Construct the $104.4 million Waimea Community Dam in the Lee Valley, a remote area 30 kilometers southwest of Nelson, New Zealand.

 Solution

 Benefits

  • Improved accuracy and easy-to-use, more visual touch screens.
  • Improved rock breaker precision despite drill vibrations.
  • Real-time accurate scans to track progress/ensure quality

The Nelson Tasman region, located on the northwest part of New Zealand's South Island, has suffered from multiple droughts over recent years, which has put severe pressure on the local community and businesses, including horticulture and agriculture.

In 2018, Waimea Water Ltd, a joint venture between Tasman District Council and Waimea Irrigators Limited, was established to manage the construction, operation and maintenance of the $104.4 million Waimea Community Dam. Located in the Lee Valley, a remote area 30 kilometers southwest of Nelson, New Zealand, this massive reservoir will provide a reliable water supply to the region for the next 100+ years. When complete in 2022, it will have the capacity to store 13 billion liters of water.

A first of its type to be built in over 20 years in New Zealand, the Waimea Dam is under construction by the FHTJV joint venture team of Fulton Hogan, an infrastructure construction, roadworks and aggregate supplier, and Taylors Contracting Co. Ltd., a civil construction company.

Together, the FHTJV team has combined a talented team of professionals, working with SITECH New Zealand, to deploy some of today’s most advanced surveying and machine control technologies to ensure quality of the dam infrastructure while optimizing productivity and efficiency from excavation to concrete pour.

 Rock Solid

The three-year project began in early March 2019 with construction of access and haul roads to the Lee Valley site and vegetation cleanup and the construction of one of two bridges along the access road to the dam site

The Waimea Community Dam will be approximately 54 meters high, 220 meters long and six meters wide at the crest. About 430,000 cubic meters of rock will be used to build the dam or be recycled on site.

The multi-step construction process involves excavation to sound rock level, cleaning of rock to remove all loose material and any traces of dirt, removal of clay seams and defects, material processing, conduit construction and slope protection.

Following the release of the foundation rock, dental concrete and grout is placed in any identified rock defects. Once all defects are treated, the placement of site concrete can commence, followed by the installation of rock anchors and construction of the reinforced concrete plinth and water stops. The plinth is a seven meters-wide and 300 meters-long concrete structure that provides the watertight seal between the dam face and dam foundation. This challenging scope of work is greatly increased because the plinth is on a 55% gradient.

The focus for 2020 is the completion of the diversion culvert and the diversion of the river from the south side into the 165 meters-long concrete diversion culvert. Once the culvert is complete, crews will begin construction of the starter dam in parallel with excavation of the foundation within the riverbed and filling of the reinforced rock coffer dam.

Taking Control

Critical to the design of the community dam is that it is built in accordance with the engineering specifications and that any necessary changes due to site conditions are properly quality controlled to assure the long-term viability of the dam. Crews must have the ability to adjust activities during excavation, in particular, to resolve emerging construction and geological challenges.

Along with its highly skilled crews, the joint venture team of FHTJV is relying heavily on equipment using 3D machine control, GNSS survey solutions and high-speed 3D scanning to build this large and complex structure with efficiency and accuracy.

Due to the remote location, the team set up a site-specific base station using the Trimble TSC7 Controller and the Trimble SPS986 GNSS Smart Antenna. This base station provided correction data to the machines and other SPS986 receivers being used as rovers with tilt compensation while walking or on vehicles. With Trimble Business Center software, the team combines high accuracy surveyed data with their existing surface models to generate volumetric and progress reports as well as creating new digital terrain models to send out to the machine control systems.

On the machines, crews are using a combination of Trimble GCS900 3D Grade Control System and, more recently, the Trimble® Earthworks Grade Control Platform on two dozers and four excavators.

Reece Moon, Quality Engineer with the FHTJV, says, “We’ve been using machine control for about 10 years to improve productivity and quality of sitework and material movement activities.”

The addition of Trimble Earthworks in the last year is part of the company’s continuous investment in construction technology. He adds, “This next generation machine control system adds greater accuracy and further expands our automated capabilities with cab- and blade-mounted receivers and easy-to-use, more visual touch screens. We’re seeing particular value on the excavators equipped with a rock breaker attachment. Accuracy of positioning and work completed is extremely good despite the vibrations.”

Crews have taken advantage of Trimble Earthworks 3D with Automatics as well. In the Automatics mode, the operator controls the stick and Trimble Earthworks software controls the boom and bucket to achieve design grade.

The FHTJV is transitioning machine control to rollers as well for improved compaction monitoring over the course of the construction.

Quality Check

Along with the machine control capabilities, the construction team is using the Trimble SX10 Scanning Total Station for as-built surveying, imaging and high-speed 3D scanning.

Moon explains, “We need a way to track progress and compare slopes, compaction conditions and address issues as they arise. However, the dam surface is so steep that we would never be able to physically verify progress and assess compaction or slope accuracy. And drones would not provide the necessary accuracy on such steep slopes."

Using the local network positioning system, the SX10 offers the flexibility to move around the large site as needed and gather point cloud data to centimeter accuracy. After the first demonstration, the surveyors and project managers were sold.

Today, the FHTJV performs at least five scanning pickups a day at various locations on the job. The data is then processed through Trimble Business Center and integrated with the point cloud and survey data into one file for analysis.

For instance, the image below shows the patchwork scan with a wire model of the internal culvert structure. With this information, the team can immediately see if the as-dug conditions match the as- designed plan to within centimeters. The point cloud information is immediately processed within Trimble Business Center and then overlaid with the design data.

The team uses the geo-mapped data daily to check progress and quality. The scan data is overlaid with the design data to ensure each layer, from excavation of rock and removal of clay seams to rock cleaning and compaction, are completed to specification.

The following image shows all of the finished surface scans patched together as one as-built foundation surface.

Moon confirms, the SX10 has become the most valuable piece of new technology on the site and in our company. It's fast, the data is accurate, and it's very current. It has already provided a variety of tangible quality, costing, design outputs including the ability to tailor ground anchor lengths to specific geological features, reforecast volumes to a high precision and much more. We'll definitely keep this in our toolbox for future projects."

Once the dam is in place, the reservoir will fill up naturally for several months, with the final commissioning in February 2022. The lake created by the dam will contain approximately 13 million cubic meters of water.

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