A key phase of a £13 million sewer upgrade project to support new housing in Stirlingshire has been completed after Scottish Water successfully tunnelled under the main railway line linking Glasgow to the north east of Scotland.
Photo: The new sewer pipes run beneath the M9 and the railway line
Two new parallel pipes are being installed across 2.5 miles of land between Plean and Cowie to carry pressurised waste water for treatment.
With each pipe measuring over half a metre in diameter, one of the biggest challenges facing engineers was to tunnel underneath both the M9 motorway and Glasgow to Stirling railway line.
Tunnelling under the railway line was carried out 24 hours a day for over a week to complete as quickly as possible.
Scottish Water Alliance Team Manager Steven Greenhill said:
“This is an important project addressing one of our key strategic priorities to meet the demands of Scotland’s growing and shifting population.
“The new pipes will carry pressurised waste water from Plean to Cowie, supporting new housing being built in the area.
The twin challenges of drilling underneath both the motorway and railway line required a co-ordinated multi-agency approach to avoid causing major disruption.
Two very different methods were deployed to install the pipes beneath the motorway and the railway.
Firstly, for the M9, pipe ramming was used, where a pneumatic hammer drives the steel casing into the ground, displacing soil which is later removed from inside the casing.
Due to the harder ground and greater depth required under the railway, rock augur drilling was deployed where a pneumatic cutting head bores through the soil and rock.
Drilling operations were carried out 24 hours a day for over a week to complete the work under the railway line as quickly as possible.
The project, which began in late February 2025, is being delivered by Scottish Water’s alliance partner Caledonia Water Alliance.
CWA Project Manager Richard Paterson added:
“This remains a key project in the CWA capital programme.
“The integrated project team have successfully designed, planned and executed some of the complex engineering works required to date.
“Progress remains on track to reach completion in summer 2026 to deliver the wider benefit to the local environment.”
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