A state-of-the-art tunnel boring machine called Tunnelling Tanya has reached a significant milestone and ‘broken through’ in Paisley ahead of the completion of Scottish Water’s major investment to improve water quality and the natural environment in two local rivers.
The TBM broke through in the town’s Saucelhill Park after completing the final section in the middle of a one-mile-long sewer, or waste water tunnel, under the streets of Paisley in the £17 million project.
The water company has been constructing the tunnel since autumn 2016 as part of the project, which also includes the installation of Combined Sewer Overflows (CSOs) in the town centre.
The machine broke through at the bottom of a 65 feet deep shaft when the cutting head removed the final pieces of earth and rock along the route.
On the final drive of about 280 metres, the 5ft diameter , 23 tonne TBM removed about 5000 tonnes of rock and on the entire route an estimated 25,000 tonnes.
During the construction, the TBM installed 109 concrete pipes which form the tunnel.
Speaking after watching the breakthrough, project manager Brian Boland said:
“This is a great achievement for the team as it is obviously a key moment in the project and follows two and a half years of complex and painstaking work.
“We have experienced significant engineering challenges during the tunnelling and this has meant the work took longer than we had originally anticipated. But we have overcome those challenges and I’m delighted that we have now completed the tunnelling.”
The new infrastructure, which is the biggest investment of its kind Scottish Water has ever made in Renfrewshire, will substantially reduce the frequency of spills from the sewer network into the Espedair Burn and White Cart Water in storm conditions.
The new sewer will prevent spills by intercepting the overflows from CSOs currently spilling to the Espedair Burn. It will then transfer these flows downstream to a new CSO currently being built and will completely remove the spills from the Espedair Burn.
The new stretch of sewer has a diameter of up to 1.5 metres and was installed at depths of between 4m and 20m. A total of 15 shafts were installed along the sewer route, with the TBMs tunnelling between them.
This method was much more efficient and less disruptive than using the open cut method of excavating, given the depths of the pipe and the urban location.
The project is being delivered for Scottish Water by contractors Amey working with Donegan Civil Engineering.
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