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Pont Croesor (UB212) carries the railway and the B4410 Prenteg-Llanfrothen road across the Afon Glaslyn, with the railway on the upstream side. The river is broad at this point, and the railway span of 65.25m is carried on the existing eight masonry piers. There is some uncertainty about the precise history of the bridge, but it is believed that the underlying structure was at least heavily rebuilt in 1922-3. The rail deck was removed in 1948-9, and the road deck was extensively refurbished and strengthened in 1994. After this work it encroached slightly on the railway side of the bridge, but not enough to cause a problem.
The spans between the piers vary between 7.210 and 7.565m, and the piers are not at right angles to the decks, but are on a 10-degree skew.
The new deck was designed by John Sreeves, who also designed the other major replacement bridges. The design chosen for the replacement bridge deck closely follows that of the 1922 version, but the twin steel beams are 770mm deep instead of 508mm as a result of the much heavier loading to be carried. The track level is thus higher than the original. Transverse and diagonal bracing are similar to before, but with sleepers placed shoulder to shoulder to form a continuous mat following the practice established on Phase 3 bridges. Flanking walkways and a handrail on the upstream side only are required to comply with current standards. The piers have been repaired by repointing where necessary, and the existing concrete plinths have been reused with new holes drilled for holding down bolts. Irregularities in the pier spacing prevent making all of the beams the same length. Nevertheless, in order to rationalise the fabrication work, the sixth span from the north has beams 8.405m long and the remainder are 8.230m long with the bearings offset very slightly from the pier centrelines. All steelwork is galvanised to achieve long-term corrosion protection and pre-assembled deck panels proved light enough to be lifted by a crane positioned on the road deck without damaging the highway.
Elevation, plan and cross-section drawings (PDF file, 317KB).
Design checking work was carried out by Halcrow's Cardiff office, and the contract for constructing the rail deck was let to D.J. Williams and Son of Brunswick Ironworks in Caernarfon.
Welsh Highland Railway Construction Ltd announcement, June 7th 2007:
WHRCL is delighted to announce that an order has been placed with Brunswick Ironworks of Caernarfon for the completion of the eight spans for Pont Croesor. Brunswick manufactured the three 75 foot long truss bridges which take the WHR over the Glaslyn at Bryn y Felin, Afon Nanmor and Afon Dylif, and the bridge over the A4085 Llanfrothen road near Nantmor. Pont Croesor is the last major engineering structure on the line to Porthmadog. The bridge spans, and all the other bridges listed above, were designed by volunteer John Sreeves. The pictures show the "I" beams for the spans stored awaiting fabrication at Brunswick's Peblig Mill works.
Steelwork for the bridge is seen below at Brunswick Ironworks on July 6th 2007, together with the old bunker from loco no. 87.
By August 24th this pair of beams had had their vertical plates fitted.
These views were taken at Brunswick Ironworks on October 5th 2007.
In early November 2007 about half the span sections had been completed and sent away for galvanising.
Preparatory work on the abutments and piers was done on site during December 2007. The contractors were noted on site by 0715 on Monday December 3rd, with road traffic across the bridge controlled by lights, and the lane nearer the railway coned off with contractor's vehicles parked on it. The following pictures were taken early the next day. The second picture shows work being done to remove the old holding down studs. The holes were then made good with grout, prior to the drilling of new holes and placing of bolts as part of the bridge installation.
The river was approaching flood conditions on December 7th 2007, with the walkways on the scaffolding under water. Nonetheless good progress had been made with removing the old studs using a corer. The removed cores (centre picture) revealed the old studs to have been hex-headed bolts, cast direct into the concrete. The concrete seemed to have been of good quality, using sizeable granite aggregate.
The corer holes in all the piers had already been grouted when these pictures were taken on December 9th 2007 (when the river was still very high, and some fields downstream were flooded); the small holes with threaded bushes visible in some pictures had been for anchoring the corer. Precise marking out for the new holding bolts followed very shortly afterwards. Drilled steel plates were subsequently placed over the new bolts and the top surfaces of the piers, and the bridge deck sections bear on these plates. Three of the piers showed longstanding non-structural damage on their outer upper corners.
Boston Lodge made templates for marking out the positions of the new bolts; they reflect the fact that the piers are not at right angles to the bridge, but are on a 10-degree skew.
These pictures at Brunswick Ironworks on December 11th 2007 show galvanised beams awaiting assembly, and two assembled bridge sections largely ready for installation.
The templates were in use on the bridge on December 12th 2007. The first picture shows survey gear set up near the end abutments, along the bridge's centreline. The gear was being used to check orientation of the plywood template for drilling holes for the holding-down bolts, and work was going on to position the template on the most northerly pier in the river. The second picture shows pilot holes being drilled for location dowels on the southernmost pier. The template had been located on a pre-surveyed pin, and rotated into the correct orientation using the survey gear. Once the position was confirmed, the procedure was to add a bit of weight and drill two extra pilot holes to define the template's position. The contractors would later reposition the template over each pier to allow the holes to accommodate the hold-down bolts to be drilled.
These views taken on December 16th 2007 illustrate the marked out centrelines and the newly drilled holes on the piers. This work had also been done on the abutments, which had been fitted with scaffolding for the purpose.
Following very wet weather after Christmas 2007, the river level had receded by New Year's Eve, leaving an appreciable quantity of debris carried down the river hanging from the scaffolding. The last picture shows the formation between the south abutment and the level crossing site.
Installation of the bridge by Brunswick Ironworks and Bob Francis Crane Hire was done on schedule on January 2nd 2008. The assembled deck units were brought from Caernarfon by lorry and craned into place on the specially made steel locating plates. Installing each unit took roughly twenty minutes, with gaps where the lorry had to make a trip to Caernarfon for the next load. Nevertheless all the lifting was completed by the end of work on the 2nd, allowing crane hire to be kept to a single day.
January 3rd 2008 was spent on survey and fine adjustment of the structure prior to grouting the holding-down bolts into place. The day's objective was to achieve the optimum straight line and level on the panels by jacking, packing and inserting shims to allow for small irregularities in the plinths and rolling tolerances in the beams. Following the main installation, greased rubber pads were inserted, the handrail completed and then the bolts and baseplates were grouted into position.
Work was taking place in the week beginning January 7th 2008 to complete the walkways and handrails.
In mid-January 2008 work was being done to increase the strength of the abutments. Mass concrete blocks (dowelled into the existing abutments) were cast at both ends of the bridge, as illustrated below. At the north end, formwork was being assembled prior to casting of a retaining wall for the embankment and ballast.
Retaining walls were cast adjoining the ends of the deck on January 24th 2008. Note also two deck timbers on site in the third picture.
The walls had been revealed when seen the next day, with the shuttering removed.
Scaffolding had been removed and the deck timbers were put in place (but not yet secured) on January 29th 2008.
The bridge is seen below on February 1st 2008, with rails delivered ready to be laid by the Black Hand Gang the following day.
On the weekend of February 2nd-3rd 2008 the Black Hand Gang laid the four panels across the bridge, with the outermost ones supported for 3-4 sleeper lengths beyond each end of the structure. The work also included turning over a portion of the sleepers so that the heartwood lay lowermost as per usual practice. Two full rails were left in the walkways at the south end, ready for the section crossing the road. In addition to effectively completing the bridge just a month from installation, the work at Pont Croesor was a useful task for the working party as the previous weekend's efforts had reached the limit of available ballasted trackbed further north at the Afon Dylif.
On July 5th 2008 500mm lengths of rail were cut out north of the bridge, removing fishplate bolt holes to allow the rail to be moved up to make a welded joint. The work required releasing the track screws on the bridge, which was done mechanically.
Immediately south of the bridge the road turns west through 90 degrees and crosses the railway on LC114A. The original to the RSPB's Glaslyn Osprey Project visitor centre is on the other side of the turn. The osprey nest itself is some distance away; while it is known that ospreys are not disturbed by trains or other machinery, major reconstruction work in the vicinity of the nest was scheduled outside their nesting season.
The trays to be fitted between the rails at the level crossing are seen below on May 2nd and 11th 2008; this crossing is longer than the ones at Nantmor and Ynysfor built using the same method, so two trays were needed.
Installation of the crossing was more complex than at Nantmor or Ynysfor, as the road level needed to be raised on the approach to the turn on to the bridge, and the new entrance to the Glaslyn Osprey Project site (see Pont Croesor - Traeth Mawr) had to be made prior to the road closure needed for the works, which also included completing the short stretch of railway formation between the bridge and LC114A. Gwynedd Council issued the necessary order for temporary closure of the road from points 20 metres from either end of the bridge. Work was expected to take place in the week beginning July 14th 2008, but was put back a week owing to ongoing work in Porthmadog.
Prior to the road closure, work took place to create raised retaining walls on the road edges leading to the bridge, giving an idea of the revised road level.
These views were taken on the occasion of a WHR Construction Ltd Board visit on July 7th 2008.
Volunteers assembled the special track panel for the road crossing on July 12th 2008, using the trays seen above. Signage confirmed the intended July 21st start date for the road closure.
The panel is seen on July 15th 2008, ready to be craned into place the following week, with a works train in attendance on the bridge.
These views show the scene of the level crossing works on July 20th 2008, the day before the road closure was due to start.
Work at the crossing started on schedule on July 21st 2008. The Glaslyn Osprey Project site remained open during the work, with access from the Prenteg side only.
The level crossing panel was installed on July 22nd 2008, prior to building up the road surface on either side of it. With the rails on the bridge screwed back in place, Upnor Castle was able to push the panel into position, with an excavator jib supporting the south end. Given the nature of the job, the correct level of the track had to be established straight away, and hydraulic pancake jacks were brought along for this purpose.
By the end of the 23rd the crossing panel was ready for tarmac to be laid once the road surface either side had been made up to its new levels.
The gap in the rails seen above was temporary, forming part of a process of moving rails around to put joints in the best possible positions at either end of the bridge and between the level crossings. The rails on the bridge were moved to close up the gap on July 24th 2008, creating a new one north of the bridge (first picture below). This one was remedied in turn by replacing the 14 metre closure rail at the North end with a longer one, and the removed rail was adapted to form the closure rail required between crossings LC114A & B. Also on the 24th, base course tarmac was laid either side of LC114A.
The crossing is seen below with its surface course laid, and almost ready for the road to reopen. The fourth picture shows the site after reopening on the 28th, and the fifth was taken the following day.
The traffic control at the bridge and crossing remains in place pending the completion of work on safety barriers and road markings.
On August 3rd 2008 the Black Hand Gang moved the rails which had been removed North of the bridge (see above) for use to close the gap between LC114A and LC114B, before going to Dinas (their third work site of the day, having started on the CTRL) to split a turnout in two for transport (last picture).
On August 8th 2008 the welding contractor was working on the rail joints on the northern approach to the bridge, having completed the welds at both ends of the LC114A panel.
Over the weekend of August 16-17th 2008 the Black Hand Gang installed new long sleepers north of Pont Croesor, to take new style guard rails. Sleepers were repositioned and repacked where the rails had been welded north and south of the bridge. Preparations were made for the rail traffic due to pass through in support of the tracklaying push onwards to Traeth Mawr; all fixings on Pont Croesor and approaches were checked, and rubbish and surplus materials were cleared from the area. Track was fettled between Hafod y Llyn and Pont Croesor, and rail was moved south - the rail bolsters are seen below on the bridge.
A works train is seen parked on the bridge on August 23rd 2008.
The last structural task to be done here is raising the height of this wall on the outside of the road curve so it can support an Armco barrier at a level that matches the new road level. Once the railway has done this, the temporary concrete barriers and traffic control can be removed.
These views show the inside of the road curve adjacent to LC114A on October 12th 2008. The wall had been raised on this side, but not yet on the outside of the curve.
For some considerable time a set of temporary traffic lights were used to control the traffic at this point. During this period the railway and the highway authoroty were in discussions about the final desing of the protective wall required. Finally in early 2010 the desing was finalised and work could comence on the required wall. The following pictures show the early sateges of this construction work The final wall will is a reinforced concrete wall with local stone facings.
The following pictures show members of the Tuesday Gang working on 10th of May 2010 to install and commission the level crossing road signals and train and point position detection equipment prior to the full opening of the crossings.
On May 22/23 the Black Hand Gang were preparing for the official opening to Pont Croesor by burying cables, installing posts for signals and control boxes, improving ballast, lowering potential high spots of surrounding ground, and generally tidying the site at Pont Croesor. As the first passenger trains were already operating to Pont Croesor all these activities had to be undertaken under the protection of yellow flag boards and between trains arriving/departing from the new platform.
The station is approached via Pont Croesor itself, then the road crossing and finally the crossing which gives access to the adjacent RSPB Osprey centre. There is also provison for a farm crossing to be used out of season. Traffic on the crossings is controlled by flashing lights or "wig-wags" which are triggered by the approach of a train. There is a run round loop long enough to accommodate a full length service train. The station currently has a single platform located on the west side of the loop. A booking office and toilets are accommodated temporarily in portacabins. Parking is available for cars and coaches.
Photographs by Laurence Armstrong 2nd June 2010
On the same day, whcih was a glorious Saturday, the Black Hand Gang were hard at work at Pont Croesor fettling the alignment at the Northern end of the platform road. Halts in their work were imposed by the regular train service 87 and 138 were the locos on duty.
The following pictures show the work from the track gang's perspective. The work involved much jacking and packing of the track as well as the moving of ballast. The purpose was to raise the track slightly as some of the coach's battery boxes had been very slightly foul of the platform edging under some conditions as the track had settled since the reopenning to Pont Croesor. The work was undertaken with the protection of P4.4 hazard and stopboards, necessary as the gang were using Duff Jacks to lift the track and generators and Kango Hammers to compact the ballast under the sleepers. The work was "very hot, grueling, dusty and thirsty work, particularly on the Sunday."
David Firth adds that the gang started by providing a positive cant on the curve from the crossings to the Caernarfon loop point. This was followed by moving the track away from the platform edge at the Caernarfon end of the platform and lifting it to give a good clearance above platform level. The dip between the point and the platform was then reduced and a positive cant provided. The gang started lifting the track further down the platform to provide a good clearance between rolling stock and the platform. This was all carried out in very warm, hot weather and the 12 volunteers were very grateful for the breaks provided by the arrival of the train services.
The trailing point mechanism was removed from the North end of Hafod y Llyn loop during the following week and and has been transported to Pont Croesor. It is intended that it will be installed at the South end of the Pont Croesor loop during the Rest of the World Gang's weekend of 26th and 27th June 2010.
As was planned the weekend of 26th and 27th June saw the installation of the trailing point mechanism at South end of Pont Croesor loop. The pictures below show the sequence of installation. First though the ground had to be prepared and two long sleepers added as a support for the control cabinet.
On the 29th June the Tuesday gang were at work at Pont Croesor and at LC118 further towards Porthmadog. For the work at Pont Croesor, posts were installed at each end of the loop line to support the 'stop' boards for when the Pont Croesor becomes a fully operational passing loop. At the Porthmadog end a cable duct was installed under LC115 to supply current to the point indicator light and home signal, whilst those cables over the river bridge were tidied into cable ties and secured to bridge sides.
Tuesday 29th June saw contractors form Hereford at work at Pont Croesor erecting the new station shelter as seen in the left hand picture. The shelter is not being finished in the wooden cladding and slate roof as are other waiting shelters of this type on the line and instead has a corrugated sheet finish. The contractors completed the assembly the following day, the 30th June, and the right hand picture shows its completed looks.
Some further view of Pont Croesor show the North Wales Black Hand Gang working alongside the new shelter on the 3rd July 2010. The track gang were completing the task of re-adjusting the track position in relation to the platform edge, a task started a couple of weeks earlier as shown a few paragraphs higher up on this page. The last picture shows the completed South end loop point and the stop board posts erected by the Tuesday Gang earlier in the week.
Whist on Saturday the weather had been very kind there was a distinct lack of Kango Hammers with which to tamp the track so it had to be hand packed. By Sunday the weather had deteriorated to wet and windy, however Kangos were made available courtesy of the FR at Minfford .
With the track along the platform edge having received quite a bit of attention during the past few weeks there was a need to realign the approaching track from the point up to the platform as the dip there was now quite pronounced. Therefore on Sunday the 15th July the Rest of the Word Gang spent the day packing the track there. That was when the activity was not interrupted by the arrival of the service trains.
3rd September 2010:
Simon Melhuish reports: the Rest of the World Gang were working to install cabling for new signals for through-running at Pont Croesor. This included a heavy-duty mains feed to the operations room in the platform shelter, and armoured cables to the "ladybird" signals north and south of the station.
Other gangs worked this weekend in the Porthmadog area and at Waunfawr.