Report - - Merthyr / Abernant Tunnel, South Wales, June 2012 | Underground Sites | 28DaysLater.co.uk

Report - Merthyr / Abernant Tunnel, South Wales, June 2012


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Visited with wonkycows and a non member.


In 1845, Isambard Kingdom Brunel surveyed and prepared parliamentary plans for the Vale of Neath Railway which involved a 2,497-yard hole through the hill between Merthyr Tydfil and Aberdare, the second longest of Wales' tunnels. 650 feet below ground at its deepest point, it was built to accommodate broad gauge and formed part of the 6¼-mile Gelli Tarw Junction-Merthyr extension, opening on 2nd November 1853. It regularly takes two names - Merthyr, which is to its east, and Abernant.

The contractor (Mr Davis) sunk two construction shafts, 1,280 yards apart, from which he drove 7-foot headings. One of these shafts was 282 feet deep. A system of troughs and fans pumped air down to the face whilst a 1-inch diameter pipe forced water at high-pressure through ‘roses’ into the workings to clear the powder-smoke hanging in the air after blasting.

A third rail was added to the predominantly single track route in 1863, allowing GWR trains to reach Swansea. The broad gauge rail was removed and the line converted to standard gauge on 11th May 1872.

In the mid-1870s, the tunnel partly collapsed as a goods train passed through, almost burying the locomotive. Locals declared the structure to be dangerous, a claim unsurprisingly contradicted by the investigating officer. Subsidence caused by mining beneath the tunnel later resulted in part of the structure settling by 10 feet.

The S-shaped bore has masonry walls and a brick-lined roof. Close to its centre are two platelayers’ cabins. At the western end, for around 400 yards, the bore is wide enough for a double track layout; two small buildings mark the point where it suddenly becomes single.

The route was closed to traffic on 31st December 1962.


Four days after our last trapse through this tunnel, BRB(B) got into action and repaired the gates at both ends with big fuck off metal sheeting and lots of grease. Being the nosy type, I wondered why as this place is in the middle of no where and anybody who wants to go knacker drinking or devil worshipping in there is doing it well out of the way ! Also, wonkycows just missed out on going through before the new fencing and wanted to have a look. Nothing much has changed apart from the tunnel seeming a lot wetter.

1. Abernant end

2. Tunnel doubles about 300 yards in with room for a few workers cabins

3. Fireplace in one of the cabins

4. Looking back

5. Enlarged workers refuge with a fireplace

6. The drainage system, minus the piping, in action

7. Centre section, deepest point at nearly 700 feet

8. Mormon church still present in the old platers cabin

9. Approaching the Merthyr end of the 'S'

10. Light from Merthyr without any Skinheads

11. The re-inforced Merthyr portal

Thanks for looking.
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