Cracked pipes ‘no impact’

THE $500m recycled water pipeline to South Stradbroke Island is causing practical challenges with engineers dealing with cracked piping.

New councillors have been told a tunnel-boring machine had reached the exit shaft at the island, but there were problems with a section of piping 10-20m below the Broadwater.

The Bulletin asked the council several questions about the piping, but officers remain confident about the progress of the project, designed to help cope with massive population increases in the city’s north in the next two decades.

“The pipes that have cracked have been installed to form a tunnel or a sleeve between Quota Park and South Stradbroke Island,” a council spokesman said.

“Our final carrier pipes for recycled water will be concrete encased inside the tunnel. Given that, it is not expected that cracking in the pipes which form the tunnel will have any impact on the final outcome of the project.”

Officers admit the project is one of the most challenging and unique among major engineering assignments in Australia.

Key components are two marine crossings, two pump station upgrades, a pipeline on South Stradbroke Island and future plans for a “deep ocean release”.

“The combination of diameter, 2.5m externally, and length, 1380m of the tunnel, plus the mixed geotechnical conditions from sand to soft and hard rock qualifies this as a large and technically difficult pipe-jacking project,” an officer said.

“The pipe is also located under a waterway, therefore creating both environmental and site constraints in a highly populated area, adding to the project’s complexity.”

The council confirmed the northern works section, costed at $97m and crossing the Broadwater, would be completed by September.

The Nerang pipe crossing and connection at the southern end was completed in June 2020, and the connection at the northern end in Waterways Dve, along with ancillary works connected to the roadworks project, were being completed before disestablishment in September.

An exit shaft in O’Connell Park and pipework connection in Ocean St started in June, and tunnelling is to start in November from Quota Park towards O’Connell Park. A final pipeway connection on South Stradbroke Island is expected early next year.

The current system has been operating since 1984 and relies on second-treated water being pumped across the Broadwater from Labrador to an outfall at the western tip of the island on the northern side of the Seaway.

A second underground pipe from the Nerang River through Main Beach connects to the southern side of the Seaway.

Both systems are limited because they only operate on the outgoing tides to control the nutrient load in the Broadwater.

Division 10 councillor Darren Taylor said he “fully supported” the project.

“Stage one has been completed with underground pipeline now installed from Surfers Paradise to Main Beach,” he said.

“The tender process is under way for stage two construction works between Main Beach and The Spit.

“The city is working towards completion of the tender process by October and key construction dates negotiated with the contractor.”