Berwyn Viaduct Progress - part three

David Symonds Associates

Llangollen Railway Civil Engineer Steve Jones continues ...

All concrete saddling work over all the arches is now complete, including shaped 'benching' into the existing arch drainage holes and formation of smooth surfaces lipped up the parapets at either side of the saddles.

Arches 4, 5, and 6 have now had 1 coat of black bitumen waterproofing paint, but due to the inclement weather work on this item had to be stopped late last week.

The platform support beam is now concreted in place over arches 4, 5, and 6, whilst the reinforcement steel and timber shuttering have been laid out for the length over arches 1, 2, and 3.

An area has been prepared across the west end of the Viaduct to receive a rubble filled 'cut off' drain. This will act as a giant soak-away, taking the ground water that filters under the track through the railway formation, flowing down from the former siding area, and dispose of it into the adjacent river. This will prevent it from reaching the Viaduct's fill material as has happened in the past.

Scaffolding has now been erected up the full height of the Viaduct and over the full length of arches 1 to 5 inclusive on the A5 / Road side, and arches 1 to 4 inclusive on the river side. Arch underside ('Soffit') scaffolding has also been completed within arches 1 to 3, whilst a start has been made within arch 4 to bridge the stream with a partially suspended scaffold ledged onto the steep ground on the A5/Road side.

vegetation

Above: With the scaffolding in place, the viaduct can be inspected at close quarters. Civil Engineer Steve Jones inspects some of the vegetation damage to the North face of arch 1. The surrounding loose brickwork has had to be completely removed for rebuilding.

Work has commenced on partial removal and reconstruction of the end of the existing station platform outside the station house. This is to ensure that a 1:20 gradient ramp is provided between the existing and new platform structures. The problem is that the Viaduct platform will be designed to a modern 3ft standard height; the existing 1865 Berwyn platform is non-standard, being up to 3" to 4" lower in places. The stiching anchors for the arch repairs have been delivered and are now in store; preparation work is in hand to commence the process of drilling and inserting the anchor bars into the structure where scaffold access is now complete.

repointing

Above: Repointing work in progress.

Finally, works to renew the pointing of the south elevation are continuing to progress on the elevations of arches 1 and 2 South (A5/Road) side. The badly eroded joints in the masonry can be seen on the left. The pocket has been cut out of the top of the parapet wall ready to receive a support brackets for the platform extension.

This week it is hoped that all the arches will receive their black waterproofing paint coat, weather permitting, and that the east half of the platform support beam will be concreted. Once these items are finished work will then commence on the backfilling operation to bring the fill level over the arches back up to formation height so that we may then reinstate the railway track. Backfilling will hopefully be going on next week, and take about 1.5 weeks to complete.

Photos by John Joyce


Berwyn Viaduct Progress - part four (23/02/2002)

overview   overview

Above: General views of the site on Saturday 23rd February.

The concrete saddles, waterproofing and drainage works have now been completed, and the whole length of the platform support structure has been cast (along the left-hand side of the trackbed). The platform support beam has been marked up ready for drilling out of holding-down bolts for the platform support columns. Following on from that, the structure has been neatly backfilled to bring it up to ballast level. The track will be laid and ballasted, and then lifted up to the correct level. It should be possible to complete the reinstatement of the track it in time for the scheduled reopening on 23rd March.

scaffolding   overview

Above: Scaffolding is now in place over much of the structure. The River side of arches 3 to 5 remain to be scaffolded.

The previously suggested novel overhead gantry support system has now proved unnecessary. The Rivers Authority eventually relented their original restrictions and have agreed that a conventional ground supported and structure tied system can be erected, provided that it effectively spans the entire width of the stream and has no footings directly adjacent to or at the same level as the stream bed. This has been ensured on site by the construction of mass concrete footings on the river bank, and smaller scaffold 'bank seats' at higher level either side of the stream, from which will be built free standing scaffold towers and long span heavy scaffold beam units to support conventional decking under the arches.

The concrete bases will be left in place on completion of the works, so that they can be utilised for maintenance scaffolding in future years, and they will also have an additional benefit of offering effective scour protection to the bases of the slender river side piers. It has been agreed that a layer of rock waste 'Rip-rap' scour protection rubble will be laid over the bases on completion of the job to disguise them and maintain the historical ambience/natural environment of the area under the structure. Some similar scour protection works are also to be carried out to a stream undercut area at the base of the pier between arches 4 and 5.

north side   down!

Above: The size of the structure becomes much more apparent from the scaffolding ...

The views above give some impression of the overall size of the structure. The scale of the vegetation problem can be seen on the hitherto unscaffolded part of the structure. The arch faces will have to be completely removed and reconstructed. The concrete pads around the bases of the arches will serve as a base for the remainder of the scaffolding structure.

crack   tie

Above: The longitudinal crack under one arch, and the close-up of one of the 'Cintec' stitching anchor fitted

The left-hand photo shows one of the longitudinal cracks which have opened up under several of the arches. The parapet walls were beginning to separate away from the arch barrels due to frost damage, in this case by a up to 3". The surrounding brickwork of the parapet wall is loose.

The right-hand photo shows the installation of a 'Cintec' stainless steel stitching anchor. These anchors, which are typically 4' to 5' long, are being fitted to tie the walls back to the arch barrels. The end of the anchor is recessed behind the outer face of the parapet wall, so that a thin sliver of brick can be fitted to cover it. In this way the external appearance of the viaduct is unchanged. All of the anchors are now in place, although some still require facing with brick. The surrounding area awaits repointing.

trackbed   pumping concrete

Above: Work in progress on 22/02/2002

In the left-hand photo 'Thomas' and 'Diesel' look on from the temporary buffer stop as spoil is removed from the trackbed beside Berwyn platform. The arm extending across the viaduct in the right-hand photo is a Pochin mobile concrete pump which was being used to supply ready-mixed concrete for the scaffolding foundations shown above.

Photos by John Joyce and Eric Keen