Cefn-Glas Tunnel and Approach

Opened : 1851

Closed - 1964

Engineering Code: ?

Cefn-Glas Tunnel was built to take the extension of the GWR route from Pontypool to Neath. Lying on the section between Treharris and Aberdare, the route parallels the still in use TVR Cynon Valley Branch. The route was abandoned before the 1960's, altough the uppermost section of the Cynon valley section remained in use as a coal siding untill the late 1970's. The line was only single track. Cefn-Glas tunnel itself cuts through the southern portion of Craig-yr-Efail between the A470 (the twisty bit just north of the Abercynon roundabout) and the A4059 Cynon Valley road and is about 650m long. The tunnel itself is mostly straight, with just the 50m at the western portal curving slightly northwards. It is therefore not possible to see along the length of the tunnel. From the photos below, it does not appear that it is blocked in any way, although I did not go all the way through. Although originally fenced off, the mesh fencing at theis portal has long-since gone, leaving only a couple of concrete posts by the entrance. The first 20-30 m are quite debris strewn ( rubbish, not tunnel roof material) although the tunnel itself is mainly dry. Being a single track tunnel, it has a large number of railway worker refuges dug into the walls, some of which are graffiti'd in the sequence 1) Stop! Turn back now!, 2) You F***ng idiot, go back!, 3) Stop! go no further. All are also emblazoned with a red and white skull motif. This sequence lies about 150m into the tunnel. I firstly assumed these were to scare people off as a joke, but despite the comical nature of the graffiti, this tunnel IS DANGEROUS!!! Parts of the brick lining towards the centre of the tunnel have collapsed. Due to the number of brick linng repair marks, collapse was obviously a problem even when tue tunnel was in use. Although the tunnel is not blocked, more bricks may fall at any time. Since some of the strength of the tunnel roof is within the brick lining, this weakness could cause the tunnel to collapse entirely at some stage.

The tunnel is lined in part with stone blocks, these belong to the Pennant Sandstone group, mid Carboniferous age that lie stratigraphically above the coal measures. The hard Pennant Sandstone forms the hills between the coalfield valleys. Portions nearer the centre of the tunnel are bare rock, with only the roof arch being bricked. In parts this looks quite clean, but in others, mineralisation has covered the brickwork. Towards the east portal, a large volume of water flows into the tunnel after heavy rain. The floor was also very wet as a the east cutting drains into the tunnel. There are occasional drainage pits in the tunnel floor, obviously drainage was a persistant problem here.

Looking outwards from west portal	Eastwards from the same spot, point of light is eastern portal	Tunnel roof, brick lined, note 'orb' effect in flash photo	Tunnel wall, note brick lined upper, stone wall lower construction
Tunnel wall, patched crack	Mineralised tunnel roof	No, not a mistake! This is the trackbed ballast	Rail worker's refuge, placed to workers could duck away from a train, rear is natural stone
Wet, stone wall backed refuge	Brick backed refuge	Graffiti'd refuge	Collapsed bricks
Rocks in a refuge	Calcite drip	Brichwork	c
Up in the roof	Drainage	Eastern portal	Refuge near east portal
Eastern end	West from east portal	West from east portal	Outwards from east portal

Tunnel approaches 9 images

	West portal from approach cutting	West portal from approach cutting
Footpath underpass in Cynon valley	Trackbed facing east towards tunnel entrance, located by the trees in the middle left	Treharris from the summit of Craig-yr-Efail in the early 1900's. The GWR line crossed the viaduct in the foreground, now demolished.
East Portal	East Portal	Cutting east from portal, blocked by A 470 embankment after 100m

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