Each year, the City of Gold Coast, in Queensland, Australia, attracts more people to its long and sandy shores.
By 2050, the population is expected to 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.
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 2,500-mm diameter pipeline pulled under the Broadwater Crossing between Quota Park and South Stradbroke Island using a tunnel boring machine.
- A 1,200-mm diameter, high-density polyethylene (HDPE) pipeline pulled under the Nerang River bottom between Winchester Street and Waterways Drive with horizontal directional drilling.
For a company like GEM Industrial, headquartered in Leongatha, Victoria, Australia, which specializes in many of the more complex 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.
GEM fused 900 m of Iplex 1,200-mm SDR 11 HDPE 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, GEM fenced off a work staging area and adjusted that parameter daily as more and more was fused. GEM had six to 12 crewmembers working around the clock on any given day so that the beach could reopen as soon as possible.
One of the more challenging aspects on the job was the pipe itself, which in places was up to 140-mm 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 percent pass rate.
GEM performed four to five welds a day for a total of 75 fusions using a McElroy MegaMc 1600.The powerful hydraulic system, which aids in clamping and lifting the pipe, was extremely helpful for handling the thick pipe GEM also recorded each step of the fusion process using a McElroy DataLogger. This lets operators know that the correct temperatures, pressures and heating/cooling times were following during the fusion. 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 size of the borehole. With the aid of gyroscopic and radar guidance tools, pilot holes were dug on either side of the Nerang River before drilling under the riverbed from each side until they met in the middle.
To ensure the borehole was big enough for the pipe, they used Sharewell reaming passes in three different sizes up to 58 in. They also designed a double-ended pulling head to test the bore profile. Later, it was cut in half and welded to one of the halves to the pipe string.
Once complete, they were ready to pull back the 900-m preassembled pipeline under the Nerang River.
Floating the Pipe
The 900-mm buoyant pipe string was towed for 5 km, escorted by an assortment barges and tugs. Once the preassembled pipeline was pulled onto shore and aligned at the entrance to the borehole, it was connected to the drill head and into the hole for the pull. Due to the pipe size and weight, 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 1,200-mm pipe weighing some 300 tons. The process took about 30 hours.
When the pull was complete, the HDPE flange connections were butt fused and the pipe was connected to the existing network.
GEM tends to take on projects that are a little more challenging as opposed to less complicated, straight-line projects that are typically very competitive. “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,” 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.