Each year, the City of Gold Coast attracts more and more people to its long and sandy shores. By 2050, the population is expected double to 1.2 million people. While this places significant demands on the city’s 1980s pipeline water infrastructure that is near capacity, the city is planning ahead on a large scale.
To start, the city has recently improved and expanded its water recycling network by constructing two of the longest marine pipeline crossings of their kind in all of Australia.
As one of the biggest users of recycled water among urban utilities, the City of Gold Coast captures and treats millions of liters of wastewater for irrigation. This offers Gold Coast businesses and industries a sustainable water solution that also helps reduce expenses while conserving valuable drinking water in a region commonly exposed to drought.
The first phase of the city’s Long Term Recycled Water Release Plan was no simple feat. The $70 million investment included upgraded pump stations and release points on the Gold Coast Seaway and construction of the two pipelines to handle the increased volume of excess wastewater that is treated and reclaimed, then pumped throughout the city to irrigate golf courses, parks and more.
To avoid disruption to one of the country’s top tourist destinations as well as the pristine beach environment, the two new pipelines were installed beneath waterways and riverbeds using trenchless methods:
- A 2,500mm diameter pipeline pulled under the Broadwater Crossing between Quota Park and South Stradbroke Island using a tunnel boring machine
- A 1,200mm diameter, high-density polyethylene (HDPE) pipeline pulled under the Nerang River bottom between Winchester Street and Waterways Drive with horizontal directional drilling (HDD)
For a company like GEM Industrial, headquartered in Leongatha, Victoria, which specializes in many of the more complex high-density polyethylene (HDPE) pipe projects, it was an exciting opportunity to be part of an infrastructure solution that will have a lasting and sustainable presence.
“All our guys on the project were really proud to be there,” said Darren Chandler, owner of GEM Industrial. “It’s a beautiful part of the world and definitely a great project to be involved with for sure.”
Their role was to fuse a new pipeline to handle the increased volume of excess recycled water that can be released at the Gold Coast Seaway with flow rates of up to 3,316 L/s.
The Gold Coast coastline, which stretches for 70 kilometers, provided GEM’s pipe fusion crew a gorgeous environment for fusing pipe. Beach lovers flock to Surfers Paradise for boating, swimming and surfing, and there’s no shortage of theme parks, shopping and nightlife on the waterfront.
GEM fused 900 meters of pipe at what is known as “The Spit,” which is the northern most part of the Gold Coast that stretches into the seaway. Since this is a public beach area with lots of people, GEM fenced off a work staging area and adjusted that parameter daily as more and more Iplex 1200mm SDR 11 HDPE pipe was fused.
GEM had six to 12 men working around the clock on any given day so that beach could reopen as soon as possible. Ironically, the corona virus helped in that aspect because the beaches were starting to clear out towards the end of the project in April and May.
One of the more challenging aspects on the job was the pipe itself which in places was up to 140mm in thickness. To ensure integrity of the fusion joints, test pieces of the butt-fused joints were destructively tested by the ALS Brisbane Association of Testing Authorities (NATA) accredited lab for adherence to ISO 13953:2001 of polyethylene (PE) pipes and fittings with a 100% pass rate.
Chandler has a saying about this process, “We write the recipe, we bake the cake and we then taste the cake.” In other words, they write the recipe on how the pipe is welded, they weld the pipe and then they pull it apart to see how it performs.
GEM performed four to five welds a day for a total of 75 fusions using a McElroy MegaMc® 1600, a rugged fusion machine which is situated on a wheeled chassis for easy portability to the jobsite. All of the MegaMc machines are equipped with a powerful hydraulic system which aids in the clamping and unclamping of the jaws while hydraulic pipe lifts handle the pipe coming in and out of the machine.
The MegaMc 1600 was used in conjunction with a McElroy DataLogger® to record each step of the fusion process. This lets operators know that the correct temperatures, pressures and heating/cooling times were following during the fusion. Chandler said GEM data logs every joint on every job because of the peace of mind and comfort in knowing that the correct procedures were followed.
“The guys in the field can compare the joint to the log and know they got it right. If there’s any doubt, we don’t have an issue with cutting a joint out,” he said. “It’s definitely a good practice.”
Before the pullback, GEM removed the internal and external fusion beads, and conducted hydrostatic pressure testing to ensure the pipeline was leak-free.
The drill and the pullback
The HDD contractor, Dunstans, had its own set of challenges due to the geology, location and the size of the borehole. They began by digging pilot holes on each side of the Nerang River and drilling under the riverbed on each side until meeting up in the middle with the aid of gyroscopic and radar guidance tools.
To ensure the borehole was big enough for the pipe, they used Sharewell reaming passes in three different sizes up to 58 inches back and forth. They also designed a double-ended pulling head to test the bore profile. Later, they cut it in half and welded one of the halves to the pipe string.
Once that was complete, they were ready to pull back the 900-meter preassembled pipeline under the Nerang River, Gold Coast Light Rail and the Sundale Bridge from Waterways Drive on Main Beach to Winchester Street.
Floating the pipe
Transporting the 900mm pipeline to the pull site was an interesting spectacle. The buoyant pipe string was towed for five kilometers, escorted by an assortment barges and tugs along with the Gold Coast Water Police. Because the density of HDPE is slightly less than water, it will float even if it’s full of water.
Once the preassembled pipeline was pulled onto shore and aligned in the direction of the entrance to the borehole, it was connected to the drill head and into the hole for the pull. There was a lot going on at the entrance point at the edge of the sea. Half the roadway was closed and five excavators were deployed to hold up the massive pipeline as it was guided under the riverbed.
Chandler said they have had longer pulls of their pipelines before but never 1200mm pipe weighing some 300 tons. The process took about 30 hours.
“It was really complicated and they did an excellent job,” Chandler said.
Once the pull was complete, the HDPE flange connections were butt fused and the pipe was connected to the existing network.
“We prefer to do that. We’re really comfortable with the outcome. We have great confidence with all butt fusion really,” Chandler said.
2020 was actually a good year for GEM project wise. They did a couple of jobs on the east coast including one in New South Wales.
“We haven’t really stopped,” Chandler said. “It’s been quite positive other than logistics. Mobilization across the country during covid has probably been the hardest, but there’s been plenty of work.”
GEM also tends to take on projects that are a little more challenging as opposed to less complicated, straight-line projects that are typically very competitive.
“But if you get into stuff that’s a little unique, a little bit different, that needs a little bit more thought, a little more process involved — I think that’s our niche for the moment,” Chandler said.
Construction spread out over a nine-month period, but public disruption was minimal considering the scope of the project and the City of Gold Coast now has a leg up on the future by serving more people through better infrastructure.