Toadmoor Tunnel

{{Short description|Railway tunnel in Derbyshire, England}}

{{Use dmy dates|date=September 2017}}

{{Use British English|date=September 2017}}

{{Infobox tunnel

| name = Toadmoor Tunnel

| image =

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| official_name =

| other_name = Hag Wood Tunnel

| line = North Midland Railway

| location = Ambergate, Derbyshire, England

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| status = In use

| system = Rail

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| opened = 1840

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| owner = Network Rail

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| traffic = Rail

| character =

| engineer = Frederick Swanwick

| construction = Cut-and-cover, brick arch, stone retaining walls and invert

| length = 128 yards (117 metres)

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| extra = Grade II listed, part of Derwent Valley World Heritage Site

}}

File:Toadmoor Tunnel.jpg

Toadmoor Tunnel (originally called Hag Wood Tunnel) was built at Ambergate in Derbyshire, England, as part of the North Midland Railway, which opened in 1840.Jewell, R., (1995) Images of Belper & Ambergate, Derby: Breedon Books

128 yards long, it was cut through an unstable hillside on a notoriously difficult line of route. What had initially been expected to be acceptably strong coal-bearing rock turned out to be wet shale. On beginning excavation a landslide occurred, the effects of which can still be seen further up the bank in Thatcher's Wood.Alan Baxter and Associates in World Heritage News, Issue 14, 2014, Derwent Valley Mills Partnership

The engineer Frederick Swanwick decided to proceed using the cut-and- cover method, with stone retaining walls and invert, and a brick-built masonry arch over the top, which gives it its unusual elliptical shape. Because of this, it took 15 months to build, instead of the planned two.

It is thought that a second landslip may have occurred sometime later, so that it was braced with steel hoops at its southern end.

Because of the tunnel cross section the depth of ballast under the track is adequate in the centre but almost nothing close to the walls, which produces settlement in the middle and crushed ballast at the edges.[http://www.bbrail.co.uk/news-article/XiTrack_slab_track Balfour Beatty: Polyurethane slab track 4 August 2014]

Other problems arise with a need for increased line speed and the arrival of electrification, not least because it is grade 2 listed and part of the Derwent Valley World Heritage Site.