A crucial phase of a £13 million sewer upgrade project in Stirlingshire has been completed, following Scottish Water’s successful tunnelling operation beneath the main railway line connecting Glasgow to the North East of Scotland.

The infrastructure upgrade is designed to support new housing developments in the area.

The project involves installing two new parallel pipes across a distance of 2.5 miles (4 kilometres) between the settlements of Plean and Cowie. These pipes, each measuring over half a metre in diameter, will carry pressurised waste water to a treatment facility.

A major engineering challenge was executing the installations underneath two major transport routes: the M9 motorway and the busy Glasgow to Stirling railway line.

Steven Greenhill, Scottish Water Alliance Team Manager, confirmed the completion of this difficult stage: "This is an important project addressing one of our key strategic priorities to meet the demands of Scotland’s growing and shifting population."

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He added that the successful tunnelling operations were the result of a coordinated effort: "The twin challenges of drilling underneath both the motorway and railway line required a co-ordinated multi-agency approach to avoid causing major disruption. We are grateful to all involved for their help and support and I am particularly pleased tunnelling operations have been successfully completed."

Engineers utilised two distinct techniques for the subterranean work:

1. Under the M9 Motorway: Pipe ramming was used, involving a pneumatic hammer to drive a steel casing into the ground, with soil subsequently removed.

2. Under the Railway Line: Due to the harder ground and the requirement for greater depth, rock augur drilling was deployed, using a pneumatic cutting head to bore through both soil and rock.

To ensure minimal disruption, the work beneath the railway was carried out 24 hours a day for over a week.

The project, which began in late February 2025, is being delivered by Scottish Water’s alliance partner, the Caledonia Water Alliance (CWA).

Richard Paterson, CWA Project Manager, confirmed that progress is on schedule: "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." He concluded that progress "remains on track to reach completion in summer 2026 to deliver the wider benefit to the local environment."