Providing us with an example of Victorian civil engineering at its very best, and striding majestically as it does across the wide and flat valley of the River Dane, the viaduct at Holmes Chapel looks magnificent from any viewpoint. Also known locally as Twemlow viaduct, it has been described as one of the finest viaducts in Cheshire.
Designed by George Watson Buck, engineer-in-chief to the Manchester and Birmingham Railway, it was constructed in the early 1840s. A workforce of about 500 navvies grafted for two years in the pay of Messrs. Tomkinson & Holme of Liverpool to build it. Conditions were squalid and several lost their lives.
Holmes Chapel viaduct ranks as one of the largest brick structures in Britain, having 23 semicircular arches, each with a span of 18 metres and resting on three metre by eight metre piers. It reaches a maximum height of 25 metres to the parapet and it has a length of 520 metres.
These details are impressive enough, but this structure also stands in proud testament to the brave determination and can-do attitude of this country’s railway pioneers. The viaduct is an object of beauty in its own right – it has been said that a test of great architecture is that it should enhance its surroundings and that is certainly the case here.
Approaching Holmes Chapel village on the A535, the viaduct begins to loom large. Getting in closer, we can see that its elegant piers and spans are constructed of red brick, with sandstone spring courses and sandstone parapets.
Recently, however, when looking in greater detail still, it would become apparent that everything was not entirely as it should be. The evidence of stained and spalling brickwork, efflorescence and visible cracking all pointed towards serious water penetration. For 175 years this structure has carried the main line railway between Crewe and Manchester Piccadilly and, like most structures of its era, it has required some occasional minor repairs. Now the time had arrived for some more significant remedial action.
Investigation work by Network Rail revealed that the viaduct had failed waterproofing and drainage. All of the piers were affected and there were also some instances of spandrel separation, manifesting itself as longitudinal fractures around the arch barrels – the crack locations coinciding with the width of the parapet walls.
It also became clear that the original drainage system was choked and completely ineffective. A longitudinal drain in the 6-foot ran the full length of the viaduct, falling towards the southern end.
This emptied into fall pipes contained within every third or fourth pier, and therein laid a serious design flaw. The inaccessible fall pipes, together with under-track manholes blocked by permanent way work, meant that drainage problems became impossible to rectify.
Network Rail estimated that breaking out the brickwork to reinstate the original drainage system would involve at least six months of line closures. The provision of external fall pipes was therefore seen as the only realistic solution. With the structure being Grade-II listed, a sensitive solution would be required in order to gain planning approval.
With the deck waterproofing requiring complete renewal and with the need to stabilise the spandrel walls in some areas, the design solution adopted by Network Rail was simple, but unusual. It involved the use of pre-cast concrete sections to form a structural over-slab, tied into the spandrels and forming a waterproof channel that also provides ballast retention. In this way, lateral forces within the ballast are restrained by the reinforced concrete channel, rather than by the parapets and spandrel walls. Drainage outlets above each pier empty into external fall pipes.
Externally, the viaduct was estimated to require the replacement of some 68,000 bricks, whilst other areas would need cleaning, re-pointing and the removal of vegetation. The arch cracking was to be stitched by means of stainless steel ties and grouting.
Short and sharp
This was clearly going to be a large project. By undertaking the work during conventional possessions, it was estimated that the task could take up to six months. The decision was therefore taken to complete all of the works within one 11-day blockade, scheduled to take place between Saturday 13 February and Wednesday 24 February 2016. By bringing forward other scheduled maintenance work on the route, Network Rail created what it terms ‘bubble working’ – maximising the line closure opportunity and reducing the overall disturbance to the travelling public.
Although it seems undesirable to blockade such a strategically important section of the West Coast main line in this way, Network Rail judged that it would minimise the disruption overall by driving efficiency improvements.
It was estimated that a conventional piecemeal approach would result in weekend possessions over a six- month period. The ‘bubble’ tactic also generates significant cost benefits, as Joelle Caldarelli, scheme project manager for Network Rail, explained: “About £500,000 is being saved, and that’s mainly on compensatory charges to the train operators. Rather than having to come back on repetitive weekends, doing it all in one go saves tax payers’ money, which we can reinvest elsewhere on the network.”
Concurrent within the Holmes Chapel blockage, similar waterproofing works were undertaken on the nearby Peover (pronounced Peever) viaduct. In addition, there were two major bridge reconstructions, repair works to an underbridge, refurbishment of the subway at Wilmslow station, as well as a string of routine maintenance tasks.
In other words, the plan involves pulling in jobs that would have required their own line closures over the next few years. In total, the works undertaken during the 11-day Holmes Chapel Blockade have been valued at £17 million, of which the Holmes Chapel viaduct work accounts for £7 million.
J Murphy & Sons and VolkerRail
The civils contractor appointed by Network Rail for all these works was J Murphy & Sons – a company able to provide a complete solution, including the manpower and all the required plant and equipment. With very tight time constraints on the work schedule, this complete solution was considered a key advantage. The one exception was the removal and reinstatement of the track, which was contracted to VolkerRail.
During the viaduct works, one track was kept in situ at all times to facilitate the movement of materials. Starting on the Down line, the track ballast was dug out and the surface was then levelled by a 50mm sand screed.
The precast concrete ballast retention units were then laid on this to form a self-contained trackbed. These three-metre-long reinforced concrete sections were manufactured by Moore Concrete Products of Ballymena, with a total of 346 being used on the Holmes Chapel viaduct. Concrete pumped from a compound beneath the viaduct formed a reinforced stitch between the ballast retention units along the centre line of the viaduct, tying them into the parapet walls.
Above the concrete a loose-lay three-layer membrane system provides the viaduct waterproofing. A flexible polypropylene sheet from the Sterling Lloyd ‘Hytec’ range does the job, sandwiched between protective fibrous matting layers. Joints in the membrane are formed by heat welding and over each pier there are sealed joints into drain pipes that exit through core drillings to the outside face. Fall pipes are of UPVC and are disguised to have the appearance of cast ironwork.
Forming the ‘bubble’ approach, a package of works was undertaken during the Holmes Chapel blockade. Three miles down the line from Holmes Chapel, Peover viaduct has a similar construction, albeit with only ten arches. It had suffered from the same defects of failed waterproofing, brickwork damage and vegetation growth. As at Holmes Chapel viaduct, the work at Peover involved the installation of ballast retention units, the provision of a waterproof membrane and new drainage. Brickwork repairs to all ten spans were also required to refurbish this asset.
At Wilmslow, the station subway is a single-span structure with mass brick abutments supporting a precast concrete unit deck. Water was leaking through the joints between the units and through the abutments. The rectification work involved lifting the track off and applying waterproofing and associated drainage, followed by cleansing and repainting of the subway.
Hungerford Road bridge in Crewe is a three-span skewed brick arch overbridge incorporating riveted steel girders and brick jack arch widening. It had suffered severe corrosion to the girders, leading to inconsistent capacity across the structural members. Rectification work here involved replacement of the failing section.
A single-span steel bridge crosses the A34 at Alderley Edge. This bridge has had historic alignment defects. The bridge rectification works encompassed a realignment of the ballast retention.
Forming part of the Holmes Chapel Blockade contract, but actually located on the single-track freight-only Northwich to Sandbach line, the single-span overbridge at Shipbrook Road in Rudheath has cast iron girders supporting bays of transverse brick jack arches. Significant diagonal cracking of the jack arches and corrosion of the structural members had severely limited the load capacity of this bridge. It required reconstruction and extensive brickwork repairs.
Into the future
This was the first example of Network Rail’s new ‘bubble’ strategy, with the work cluster approach being calculated to bring significant cost savings and cause less disruption in the long term. Something of an experiment, this approach seems set to be repeated.
Certainly, things went well in Cheshire. Exactly on schedule, at 04:00 on 24 February, the line between Crewe and Manchester was handed back. Chris Wright, contracts manager for J Murphy & Sons, said: “With such a short timeframe to carry out a significant amount of work, this was always going to be a project that pushed us, but the team rose to the challenge. We pulled out all the stops and our innovative approach to working meant that we handed back the line to Network Rail as planned. It was gratifying to see the first train pass over the viaduct first thing this morning.”
As this issue of Rail Engineer is published, the Murphy workforce will be all set to repeat the exercise at Reddish Vale viaduct. During a nine-day blockade this 17-arch brick structure will be refurbished under an almost identical package of works.
Operations to clean and repair the external brickwork at Holmes Chapel and Peover viaducts will continue for several months, but with no disruption to rail traffic. This work will make use of lifting platforms rather than scaffolding and involves structural re-casing work, crack repairs and cosmetic attention. Unusually, at the northern end of Holmes Chapel viaduct, rope access will be necessary.
The completed waterproofing and stabilisation works at Holmes Chapel and Peover viaducts have a design life of 125 years, with no intervention being required for at least 50 years. Talking with the Network Rail and Murphy managers and staff on site, it’s apparent that they have a satisfaction in their work. It’s possible even to detect a sense of continuity with the past – an admiration for what exists and for those determined people who created it.
George W Buck would have been delighted!