Phase 3 pages:
Plas y Nant bridge
Plas y Nant
South of OB62, a short, curving stretch of line on a stone embankment brings the WHR to its last crossing of the Gwyrfai, at Plas y Nant; here, road, river and railway are squeezed close together at the narrowest point in the valley. The left-hand picture below (Jan Woods, WHLR Ltd) shows the northern end of the Plas y Nant river bridge (UB64) and adjacent trackbed on July 12th 2002, with the bridge fenced off and partially stripped. Trackbed stripping and undergrowth clearance made the adjacent WW2 base for a Home Guard "Blacker Bombard" mortar bomb launcher (see Welsh Highland Heritage no.12 [June 2001], p.6) on the trackbed much more visible (close-up view on the right); there was previously another of these bases in the Aberglaslyn Pass.
In the first days of July 2002 the contractors started establishing a new access and work site at Plas y Nant, adjacent to the river bridge and the site of the old halt. Work on this compound was suspended by the middle of the month, after a large void had opened up above an old drain in the roadside verge just where the site access crossed it. The highways authority dug out the drain, and completed a new underground drain chamber by mid-September. In the meantime a new entrance to the site compound was created, so railway work could continue.
In early August the mortar launcher base was removed intact (rather more than half its total height had been underground) and placed alongside the trackbed a few metres to the north - it had been moved again by September 21st, and may later be moved to a position by the new passing loop - and temporary props were fitted underneath the river bridge.
In early September a sandbag coffer dam was erected around the northern abutment of UB64, which was then excavated as a start to the strengthening works.
The coffer dam and associated pumping arrangements allowed the contractors to undertake the casting in situ of new foundations for the northern abutment.
A week on from the above picture, rebuilding of this corner of the abutment was at an advanced stage, in a style matching the adjoining embankment.
By October 12th, the other side of the northern abutment had been partially excavated, and a sandbag dam had been established for the southern abutment.
A week later, the base of the northern abutment had been backfilled and appeared largely complete. The original southern abutment had been completely demolished to make way for a stronger replacement. One of the bridge's cross members was also removed.
This excavation was flooded in the following week, which saw exceptionally heavy rain (left-hand picture below). Although the flow of the Gwyrfai is partly controlled by sluice gates at the outfall of Llyn Cwellyn, it also collects water flowing down from the slopes, and is thus not always predictable. Pumps were used on site, however, and a week later - despite more heavy rain - work was well advanced on the reinforcement mesh around which the base and verticals of the concrete core of the new abutment would be cast (right-hand picture).
In the following days the contractors cast the foundation slab of the abutment, and were some way into assembling formwork for casting the northern pier (like the original, this abutment incorporates a spillway) when the swollen river (which broke its banks further downstream) overtopped the sandbag dam once more.
With the river in a less violent mood - and with extra sandbags in place - both the vertical piers of the southern abutment were cast in the following week, and shuttering was well advanced for casting the top slab of the structure.
The top slab of the southern abutment had been cast by the end of November, as had the new lintel on the northern abutment. It will be noted that the iron bridge structure now stands higher above the river than it originally did, as the strengthened abutments include the height by which the ironwork had been jacked up above the old abutments.
The concrete parts of both abutments appeared complete at the end of the first week of December, and a quick start had been made on the local stone cladding of the southern abutment (left-hand picture below). Both abutments include upstands across the trackbed to retain the ends of the ballast bed on either side of the bridge.
Cladding of the vertical parts of the south abutment was largely done by December 14th. This work was carried out by specialist subcontractor Colin Jones (Rock Engineering) Ltd of Porthmadog.
In the next week a third, central pier was added to the southern abutment, reproducing a feature of the original spillway.
Cladding of the eastern side of this abutment was finished by January 11th 2003, while rockbolting was in progress on the northern abutment. The iron bridge structure had been lowered off the props on both sides, and was resting on its new footings on both sides of the river.
Scaffolding contractors were at work on January 18th, in preparation for the start of work on the span itself. The scaffolding supported a suspended plank floor underneath the bridge.
This access allowed the removal of the original crossmembers in the following days, apart from two retained temporraily to secure the sides of the span while reinforcement was in progress.
The strengthening of the span involved the replacement of the wrought iron crossmembers by steel ones, and the addition of four rolled steel joist waybeams (with vertical stiffening pieces in the webs) across the river, in place of the two timber baulks which originally carried the rails.
Fitting of the new steelwork was nearing completion when seen below in mid-February. The new steel crossmembers were all in place, with installation of the waybeams two thirds done. As the track is on a curve at UB64, each of the four waybeams comprises three sections at a slight angle to one another, to approximate the curve; the line of the track is thus off-centre relative to the bridge, and always has been here. The southern and central waybeam sections are visible below, with those at the northern end still to be fitted.
To illustrate how the new waybeams closely follow the line of the old timber baulks, compare the middle ones above with the picture below, taken in March 1997, when the timbers were mostly still reasonably intact.
The remaining waybeams arrived on site on February 19th, and are seen below being moved into position. Visible on the left in the second and third pictures are new cantilever girders fitted outside the western beam, for a private footpath for access to an adjacent property, replacing the wooden walkway built across UB64 soon after the above picture was taken. This has not significantly affected the "public" appearance of the bridge as seen from the road. The waybeams were bolted into place by the end of the week, completing the main structural alterations to the bridge.
By March 9th much of the metalwork for the deck and side rails of the walkway was in place, seen here on the far side of the southern abutment, which had some of the original crossmembers and remnants of the timber baulks stored on top of it.
Additional scaffolding was put in place to facilitate painting the bridge span, as seen below.
A volunteer working party gave the bridge its first coat of paint on March 15-16th, seen below left on the 15th. Jones Bros were also on site clearing up. By this point the short gap in the formation behind the north abutment had been infilled (right).
The painted bridge is seen below on March 22nd, essentially ready for tracklaying.
Roger Dick's pictures below shows the bridge from the walkway side four days later, including a view from the walkway side (left). It received another coat of paint the following weekend.
The scaffolding was removed in the second week of April, finally revealing the completed bridge, now also fitted with mesh walkways either side of the waybeams. While this bridge was not the quickest of jobs, the finished result thoroughly justifies the ingenuity and effort which went into it.
Track was laid around the bend leading to the bridge and across the span in the week before Easter, on closely spaced wooden sleepers. This track was temporary, to facilitate moving rails from the Plas y Nant stack to complete the remaining gaps in the track northwards.
Permanent track was laid across the bridge on July 24th, the last stretch of permanent track to be laid on the Phase 3 main line.
The bridge is seen below on August 3rd, with the guard rails fitted; Dolgarrog is under the plastic sheet on the left.
Phase 3 pages:
Plas y Nant bridge