Anyone familiar with the construction of deep tunnels will be aware of the importance of conveyor belts in taking the excavated earth and rock up to the surface to prevent the debris from simply piling up and blocking the way.
However, given the strain they are placed under, it is not infrequently that conveyor belts are damaged and their repair and maintenance is an essential service to keep the work on schedule.
This is particularly true on large tunnelling projects, which include ongoing work on the HS2 project.
Although former prime minister Rishi Sunak cancelled the northern leg of the scheme up to Manchester on cost grounds last year, the London to Birmingham section was so far progressed that it was retained and the project will now link Euston with the rebuilt Curzon Street Station on the eastern edge of Birmingham city centre.
When services do finally commence, passengers will experience a rise that passes through several tunnels. While the longest will be under the Chilterns, they will also go through the 5.6 km Bromford Tunnel on the eastern fringes of Birmingham, where excavation work has just reached the halfway point.
The digging machine, christened Mary Anne, started digging at Water Orton last year and will now complete the other half before the line re-emerges at the surface in Washwood Heath in late 2025.
It passes under the Park Hall Nature Reserve and River Tame, avoiding the mainline route taken by local trains into the city from the existing Water Orton station. The twin-bore tunnel is 47 metres deep at its midway point, with nearly 21,000 concrete segments lining the tunnel wall.
A total of 1.87 million tonnes of material will be excavated by the time the tunnelling work is completed.
Although the truncation of the project means planned tunnels under south Manchester and the centre of Crewe will now not proceed, there are still 65 miles of tunnel on the route, with an eventual total of 130 million tonnes of earth excavated, enough to keep a lot of conveyors busy and needing maintenance.
Tunnel boring machines have been used in five tunnelling projects, ranging in length from one mile for the Long Itchington Tunnel to ten miles for the Chilterns Tunnel. The majority of their work is now complete.
A further five short ‘green’ tunnels are being created using the cut-and-cover method that characterised early transport tunnels before shield boring machines were invented, a prime example of this being the oldest sections of the London Underground.
The difference with the excavated earth in the case of the ‘green’ tunnels is they will be laid on top of the tunnels to landscape them and reduce the visual impact of the line. By contrast, excavated material from deep tunnels is often taken away to create wildlife habitats elsewhere.
It remains to be seen what the next major tunnelling projects in the UK will be. In addition to the curtailment of HS2, the new government has cancelled the controversial plan for a road tunnel near Stonehenge. A decision on the Lower Thames Crossing between Kent and Essex is still pending, with the use of private funding reportedly under consideration.
