A major milestone for the Southern Pipeline harbour crossing project is close to being completed, with the outer steel pipe nearly installed under the harbour between Memorial Park and Matapihi.
The steel pipe, which is 1.6km in length, is being winched under the harbour from Memorial Park to Matapihi.
Howard Severinsen, Project Director for Tauranga City Council said: “The steel pipe is around 97 percent of the way across the harbour. There’s about 40 metres left to go. It’s gone well so far and the team are pleased with progress. However, these last few metres will be the most challenging part because we need to line up the pipe with the very middle of the steel sleeve on the Matapihi side.”
Contractors Brian Perry Civil have been working continuously since Friday to install the steel pipe under the harbour. “They’ve had to work 24/7 to ensure the pipe didn’t get stuck,” says Howard. “This is a very dynamic part of the project with lots of moving parts. We’ve had six cranes and fourteen diggers on site.”
To prepare for the installation, outer steel pipes were welded together at Memorial Park into five strings of pipes, at lengths of between 156m and 468m. The first pipe string was hoisted into the air by cranes and lined up with the end of the drill hole. It was then thrust through the hole from Memorial Park while being pulled by a drill rig based at Matapihi. The next pipe string was then craned into position, welded to the tail of the first pipe, and the process began again. Welding took about five hours between each pipe thrust.
Howard says that the drilled hole is full of bentonite mud which has been keeping the hole open and stable. “We are filling the steel pipe with water to reduce its buoyancy as it passes through the mud and to help with lining it up at the other end. The full weight of the pipe is more than 1500 tonnes. Between the thruster at Memorial Park and the drill rig at Matapihi there is more than enough capacity to move the pipe.”
Once the steel pipe is through, the plastic pipe that will eventually hold the wastewater will be winched through, before the pipe is connected at both ends to the rest of the Southern Pipeline wastewater trunk main.
From today the contractor has resumed with a single daily 12-hour shift. This phase of work was expected to take up to seven days to complete. It will take another three to four months to complete the Southern Pipeline project and reinstate construction sites back to their original states.