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Tunnelling: Uphill battle

An uphill excavator has taken innovation to new heights on the Crossrail project, helping contractors excavate escalator tunnels at Whitechapel and Liverpool Street

The team working on Crossrail contracts at Whitechapel and Liverpool Street stations were itching to get started on sprayed concrete lined (SCL) escalator tunnels linking the platform level with the ticket halls.

The ticket halls at the top of these tunnels had not yet been built, although the platform tunnels were complete. The solution was to excavate the tunnels from the bottom up, but this came with challenges.

Uphill excavation on a 30º incline would mean putting workers at risk from falling debris and rebounding sprayed concrete. To fully mitigate this, the team sought a new solution. 

BBMV joint venture, comprising Balfour Beatty, BeMo Tunnelling, Morgan Sindall and Vinci Construction Grand Projets approached GTA, a German company which has been manufacturing suspended equipment transport systems in Europe for 40 years. Between them they developed an innovative solution.

GTA specialises in suspended platforms and access ways, creating drill rigs, personnel carriers and boomers, mainly for coal mining but also for live train tunnels. But it had not created an excavator for an inclined tunnel before.

The end product is an excavator suspended from rails installed in the tunnel crown. Its job was to excavate a 6m diameter pilot tunnel which will then be enlarged to create the full size 9m diameter escalator tunnels.

For the escalator tunnels, BBMV dug a short section before anchoring rails to the tunnel crown and then suspending the 15t excavating machine from them.

The machine then moved along the rails as it cut through the ground ahead of it using an excavator bucket. New rails were added in front of the machine so the excavator could move forward. 

As the excavator advanced, more temporary works were installed to support the impressive 15t of plant. 

“The actual piece of kit has an excavating arm and a spraying arm. And a universal coupler, so you could have a man-riding basket on it, or a drill rig on it,” says BBMV project manager Peter Leyton.

Once the pilot tunnels were complete, a working platform was created in a cavern at the top of the incline, from which downhill excavation, using more traditional techniques, could take place. This is now nearing completion.

The system includes a raised walkway alongside the excavator, from which an engineer controller can inspect work and communicate with the operator in the cab.

A driver in the cab works using traditional levers, with a nozzle man working from the walkway. This walkway also functions as an emergency escape route for the operator.

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