Report - - Pencader Tunnel - Wales - Sept 14 | Underground Sites | 28DaysLater.co.uk

Report - Pencader Tunnel - Wales - Sept 14


Bajo Tierra
Regular User
Visited with a non member​

History ( FR )​

Bored through Ordovician shales, the single-track tunnel south-west of Pencader - also known locally as Alltwalis or Dolgran Tunnel - was built to Brunel's broad gauge. It formed part of the Llanpumsaint-Pencader section of the Carmarthen & Cardigan Railway, taking the line between the valleys of Skanda Vale and Dolgran.

Brunel was one of several engineers to survey the line although his was not the design finally adopted, this being longer to provide easier gradients. At 988 yards in length, the tunnel is straight for most of its length before starting to curve south close to the more northerly of two construction shafts, later used for ventilation purposes. Close to this point is a side gallery - now 'blind' - which heads horizontally to the surface, emerging close to a house. This was reputedly built as an emergency escape route but more likely was used as means of removing spoil from the excavation.

The work was contracted to Jays of London and got underway in the spring of 1857, with the heading being driven from both ends and two shafts, creating six working faces. Many of the horses used to haul away the spoil died from disease and were buried in the field in which the northern shaft is located.
In 1859, to help reduce costs, the C&C applied for Parliamentary permission to convert the route from broad to standard gauge. This was declined.

Activities were temporarily halted in May 1860 with 576 yards excavated; when they resumed, completion was expected around the New Year but this slipped to March 1861.
Construction of the railway either side of the tunnel continued for almost three years, with Holdens taking over the work from Jays. The southern approach involved numerous cuttings and embankments.

Track had been laid through the tunnel by December 1863 and the Board of Trade inspected it in January 1864, with the first train passing through on 1st April 1864. At this time it was still unlined - a watchman being appointed to monitor for rock falls.

The construction costs bankrupted the C&C which gave way to the Great Western in 1881. Conversion to standard gauge had occurred nine years earlier.
The withdrawal of passenger services came in 1965 but the line continued to carry freight until 28th September 1973.​













Thanks for looking

green godess

28DL Full Member
28DL Full Member
The tunnel has two ventilation shafts, Depths - South airshaft circa 175-ft, North airshaft circa 125-ft. In recent years the airshafts have been repaired and a new mesh has been fitted over the North airshaft; this is because members of a local abseiling organisation had been using it. I was also told that the aqueduct over the southern portal should also have been repaired, but there was no evidence that this had been the case. I was told that, after building and opening as an unlined tunnel, it took three years to line with bricks because work could only be carried out at night when the line was not in use. The tunnel is now fully brick-lined.

Both passenger and freight services ended on 16th September 1952 and the line closed to all traffic at the end of September 1973.

From the first proposals of the Carmarthen and Cardigan railway it was known that an expensive and long tunnel would be needed to take the line between the valleys of Skanda Vale and Dolgran, under the Brechfa Forest watershed. Several separate engineers surveyed the line, including Isambard Kingdom Brunel, with varying schemes. Brunel proposed a dead-straight tunnel to connect the valleys, though after reworking, the final design was longer in order to ease the gradients.

As built, the tunnel is 985 yards long, curving slightly from the southern portal in Skanda Vale, running straight for most of its length and then curving for the final third into Dolgran. The digging would require two construction shafts which could then be used for ventilation. Construction started in the spring of 1857 to bore the tunnel at the same time as work began on the first stage of the railway line in the town of Carmarthen.

During construction in 1859 the C&C railway attempted to switch from broad gauge to standard gauge, which would have meant all railway infrastructure (including the tunnel), could be built to smaller (and thus cheaper) dimensions. Such a change would require the approval of the British Parliament, and pressurisation on the company by the South Wales Railway, a broad gauge line in the area which did not want the rival standard gauge making an incursion on its territory, meant the application to Parliament never occurred.

Digging initially proceeded from four sites - at either end, and from the bottom of the first ventilation shaft sunk. Once the second shaft was finished, digging also commenced from there, though this had been abandoned by May 1860 according to a report which stated that 576 yards had been dug by this time, approximately two-thirds of the full length. Work was expected to be finished by December 1860/January 1861.

As it stood the tunnel was only 'finished' in March 1861, although at the time it was exposed rock without a brick lining, and required further work to complete it. The long approach cuttings were also unfinished at this time. During construction of the tunnel, many of the horses used to haul away excavated rock died from disease, and were buried in the field surrounding the northern of the two shafts. The same field also has grassed-over rubble remaining from cottages built by the construction navvies. Much of the spoil excavated was used to build embankments north and south of the tunnel, but large spoil heaps can be seen on the hillsides around both ventilation shafts.

Further delays were caused by the original contractor for the railway, Jays of London, abandoning the construction of the line in autumn 1861. By November however another contractor, Holden’s, had taken over the task. Work was focused on finishing several miles of railway either side of the tunnel, although easy to the north, to the south heavy engineering of cuttings and embankments slowed the work.

Track is known to have been laid through the tunnel at some point prior to December 1863, as a company report mentions an accident in that month on a ballast train en-route to Pencader, beyond the tunnel. Official government inspection was carried out in January 1864 and the tunnel opened with the rest of the Llanpumsaint-Pencader section of the line on 1st April 1864. At the time the tunnel was still unlined and a watchman was employed to inspect the tunnel for any rock falls, until it was eventually lined with brick some years later.

By the time the tunnel was finished, having taken four years to build and a further three to complete the railway approaches to it, it had crippled the finances of the Carmarthen to Cardigan Railway, which soon went into receivership. After the railway was closed to freight traffic on 28th September 1973, the track was removed. The tunnel was not demolished and remains in place.

Present State
The tunnel's present state is accessible, although it is gated and the northern portal and approach are privately owned and difficult to access due to a stream now occupying part of the trackbed. The south portal is more accessible and has a small shed near it, a former Permanent Way hut, and slightly further south are the foundations of the signal box for Pencader Tunnel Loop. The tunnel has two air shafts, located on the hillside above it. Both shafts are unlined and varying amounts of ground water drain through them into the tunnel. The north vent shaft was previously used for abseiling until maintenance work fixed a secure grating over it at the same time as the shaft's brickwork was re-pointed.

Walking through the tunnel can be difficult/dangerous due to deep mud at both ends - the majority of the tunnel is dry however as it lies on the summit of the line between Llanpumsaint and Pencader and thus any water seeping in, drains away naturally. Both portals are muddy, the southern one more so due to a burst culvert over the portal and a small dam of earth that causes water and wet earth to back up behind it into the tunnel.

Further inside the tunnel is in generally good condition due to being abandoned more recently than many disused tunnels, and the brickwork remains in good condition except for a portion near the north portal were some has been dislodged.

There is a persistent local rumour that there is an escape-shaft from the tunnel in the form of a staircase cut into a side-shaft leading to the surface. Though there is a general idea of where such a shaft would emerge onto the hillside nothing has yet been found in the fields or in the tunnel, nor does such a shaft appear on surveys of the tunnel held by the British Railways Board, whose remnant, BRB(R) British Railways Board (Residual) is the current owner of the tunnel and responsible for its upkeep.

Approximately 50-yards from the North airshaft, a small tunnel emerges into the undergrowth. According to a local resident, this smaller tunnel (about 2-ft high) used to emerge into the airshaft itself, although it is uncertain as to what purpose it served. However, it has now collapsed about 15-yards from the northern end and on entry it was impossible to ascertain where the other end came out. It is unknown whether there is a similar arrangement regarding the Southern airshaft.

Please contact me by a private email and I'd be pleased to send photo's and a diagram of this exlusive tunnel, last explored in 2005. Would dearly love to find out more about its presence and purpose.

Best regards from


The Wombat

Mr Wombat
28DL Full Member
Excellent, as always :thumb
Some interesting features in there


Irregular Member
Regular User
That's a really nice tunnel. You've got some excellent shots. Looks a really nice explore :thumb

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