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Mole cuts through railway embankment in preparation for the A9 dualling from Tomatin to Moy


By Ian Duncan

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The Iseki Unclemole Super TCS1200 is powered by hydraulics which pushes the Tunnel Boring Machine deeper underground with slurry pipes treating the excavated material from the cutting face.
The Iseki Unclemole Super TCS1200 is powered by hydraulics which pushes the Tunnel Boring Machine deeper underground with slurry pipes treating the excavated material from the cutting face.

Work is under way as Network Rail engineers prepare for the reconstruction of the rail bridge near Moy as part of advance works for the A9 Dualling Tomatin to Moy project.

The works at Lynebeg – being undertaken by Network Rail on behalf of Transport Scotland – involve the construction of a new under-bridge of the railway and under-track utility services.

One of the first tasks for the project was to create an under-track crossing (UTX) which will be used to accommodate temporary utility diversions during the demolition of the existing structure, and the installation of the new wider railway bridge.

Longer term it will also serve as an overflow outfall for an ecology pond being created next to the track.

To minimise disruption for rail passengers, Network Rail brought in a Mole – an Unclemole 1200 Tunnel boring machine (TBM) – that tunnelled 33 metres under the railway to break through a mixture of sand, gravel and rock over a period of four days.

The hydraulic drilling machine pushed deeper into the railway embankment and created a channel for the 1200mm diameter, 2.5-metre-long concrete pipes to be positioned and installed using a hydraulic jack.

Eleven concrete pipe sections were installed under the railway in total.

The traditional method of removing track sections and excavating would have caused major disruption on the railway line to Inverness due to depth required through the embankment.

The mole allowed the trains to continue to run whilst pipe sections were being installed, and at the same time embankment and track monitoring was being carried out.

Malcolm McGowan, Network Rail project manager on the Lynebeg bridge replacement project, said: “Finding ways to carry out work on the railway in a way that minimises disruption to train services is a fundamental part of our planning process and shows how we are putting passengers first.

“By bringing in the mole tunnel boring machine to excavate the channel under the railway and the hydraulic jacking rig to position the pipes, we could get the job done efficiently while keeping the line open to traffic.

“We are at the early stages of the project but are looking forward to sharing more details about the work and engaging with the wider community as we move forward.”

Nick Conroy, project manager for the A9 Dualling Tomatin to Moy project, said: “Undertaking these works in advance of the main construction contract to dual the A9 between Tomatin and Moy, helps to provide more certainty to our contractors programme for the main works contract."

The replacement of the railway bridge at Lynebeg is part of the significant investment by the Scottish Government to dual the A9 between Perth and Inverness.

The procurement process to select a main contractor to construct the next section of the A9 dualling programme between Tomatin and Moy was launched by the Minister for Transport Minister Graeme Dey last week.


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