Southern Water has reached a tunnelling milestone on its £100 million-plus Southampton Link Main underground pipeline project after a tunnel was completed deep beneath the M3 motorway.

A tunnel boring machine (TBM) started work on 6 October digging 7 metres below ground and finished the tunnel underneath the M3 motorway on 6 November. The M3 motorway tunnel is one of three tunnels in a major new water supply pipeline for Hampshire which when complete, will be connected and run to Southern Water’s Otterbourne site.

Terence Hedley, Senior Project Manager, said:

“It’s so exciting to reach another important milestone in the development of this essential project. It’s a key part of our plan to create new drought-proof sources of water for Hampshire and help keep the county’s taps and rivers flowing.

“The tunnel boring machine worked 24/7 digging its way underneath the M3 motorway for 32 days. The tunnel has an internal diameter of 1.5m and the machine was operated remotely above ground.”

Once complete, the new 19km underground pipeline will run from the Otterbourne Water Supply Works to Yew Hill reservoir, near Winchester, and then south to Rownhams Water Supply Works on the outskirts of Southampton. 

The project, which will boost resilience for water supply across the county, began earlier this year and will take around three years to complete.