Home Heritage Turning back time

Turning back time

It won’t sweeten the bitter fares pill commuters have to swallow. Ministers won’t be queuing to have their faces seen on site. There’s no great innovation; no new tech. This is engineering at its most elemental. Dirty; frontline; nuts and bolts. Far removed from the shiny façade of New Street or Crossrail’s laser-guided TBMs. But why shouldn’t we record – and celebrate – the comparatively workaday? Most of the railway is precisely that, and the industry would fail were it not for the army toiling in the shadows.

So why here, a single-track backwater that hasn’t seen regular passenger services for more than 50 years? Because this formed part of a spectacular railway, clinging to cliff tops and meandering around hills. It boasted two tunnels that never should have been and launched its trains over ravines on viaducts built from wrought iron, timber and concrete. But south of Loftus, the coastal route linking Middlesbrough with Whitby was sacrificed at economics’ altar on 5th May 1958, saving a projected £58,000 on structural maintenance costs, some of it earmarked for the mile-long Sandsend Tunnel which has since partly collapsed.

The northern section survived as far as Carlin How and was joined in 1974 by five miles of reincarnated track to serve the Boulby potash mine. Today, with the plant working at full tilt, it’s an important freight corridor. This then explains Network Rail’s ongoing project to repair another of the line’s impositions on the landscape – a Grade II listed viaduct over Skelton Beck on the southern fringes of Saltburn.

Think of a number

It’s a very distinctive structure, predominantly built in red brick but with huge rock-faced ashlar footings and a masonry oversail. Breaking the tree line to reach skywards 156 feet, the viaduct features 11 segmental arches: 60-foot spans with a 20-foot rise. The soffits look almost as good as the day they were laid, but the effects of the prevailing westerly wind and easterlies off the adjacent North Sea have taken their toll on the pier ends. Meanwhile water draining from the deck and then leaching through the brickwork has painted a consistent tide mark a few feet above springing level. The consequential damage has kept brickies occupied for decades. One of them – J Young – helpfully dated his repair: 25th October 19…well, 15 possibly, or maybe 19. Ironically, the brick he chose for his inscription has not lasted well.Saltburn(1B) [online]

The most recent project of substance saw May Gurney come here in 2006, addressing defects to four piers and three spans. Seven years on, the inspection regime has identified the need for piers 2, 3 and 4 to become the focus of attention, together with the spandrels above them. Undertaking the work on Network Rail’s behalf, at an anticipated final cost of £446,000, is Amco Rail.

Whilst the job itself is…routine, the planning and logistics have not been plain sailing. Helpfully there is a field beneath the structure which has served as a compound before, but the only access to it is through a quiet residential area, then via a steep, twisting lane. This is used by walkers – resulting in the need for large vehicles to be preceded by a marshal – and can become impassable when conditions become inclement, hence the summer programme. Actually finding the viaduct is sufficiently awkward for the fire brigade’s specialist rope access rescue team to have had a dummy run, just in case.

Amco arrived in mid-June and will have returned the field to nature by October, hopefully before the weather turns. The scope of works was initially very loose as the precise requirements couldn’t be identified until the team had examined the structure at close quarters. That demanded a scaffold with two-metre lifts and external stair towers to be tied into the structure with Excalibur bolts, initially wrapped around the three piers before then being extended across the spandrels faces. This took Rainham Industrial Services a full five weeks to erect, although substantive works started as soon as the first section had been completed, independently verified and scafftagged.

Back to basics

We don’t invest a lot of time thinking about bricks. Why should we – they are the epitome of mundane. But our railways were constructed with many billions of them, at a time when Standards – as we know them today – were unheard of. Horses and carts bore the burden of moving bulk building materials during the Victorian era, a logistical limitation that generally meant bricks would be fired as close as possible to their point of use. Quality and size was consequently variable; nevertheless bricklayers felt compelled to use whatever they were offered. So some structures comprise a hodgepodge of different bricks, complicating any subsequent refurbishment.

Saltburn Viaduct presented two key challenges. The first revolved around the aesthetic demands of its listed status. Keen to avoid more of the shiny patch repairs that are already evident on the structure, Cleveland & Redcar Council initially asserted its preference for a perforated brick that was visually similar to the originals, but was undesirable from an engineering perspective due to its greater susceptibility to freeze-thaw action and the premature bursting of its faces.

The solution came as the second issue was tackled, that of compressive strength. The bulk of the brickwork here has a rating of about 20N/mm2 or less, just a fraction of the stipulated 75N/mm2 that’s the current lower limit for engineering brick. Using the latter for repairs would have created hard spots within the structure and the potential for cracking at the interface between old and new, so the team was charged with finding a brick of comparable strength to that used in the 1870s. The closest match came from Birtley Brickworks, 30 miles away in County Durham: their 73mm Old English with F2 freeze-thaw resistance (the same as engineering brick) and low soluble salt content. The availability of this product is now being flagged up to asset management teams responsible for similar structures elsewhere.

Saltburn(3A) [online]The objective with the repairs is simply to keep the weather out. There is a basic formula: where more than 50mm of spalling has occurred, the brickwork is recased. Elsewhere they grind back perished joints to 20mm and then repoint them using a traditional mortar – four parts sand to one part Portland cement to a quarter part lime. To give you an idea of scale, around 25m2 of brickwork required replacement on Pier 2. The activity isn’t difficult, but does demand a degree of diligence and skill.

Out of sight

Amongst the problems posed by our Victorian structures is how to gain an insight into their interior design and condition. An original 1870 plan of Saltburn Viaduct suggests that the piers feature masonry slabs at 10-foot centres – tying the sides together – as well as three jack arches above at least one of them. But it’s all rather uncertain, so part of the project involves taking 75mm core samples through Pier 4 to prove whether any voids are present, possibly accompanied by a CCTV survey. “Until you look inside, you cannot determine any water damage or structural movement”, contends Paul Pickering, Amco’s Site Manager, “so the cores will help Network Rail to identify the need for future works.”

Similar activity will be carried out on the deck during a Saturday night possession, using a small rig mounted on a rail trolley. “If there are jack arches present but no inspection hatches, that means they’ve not been looked at”, explains Network Rail’s Construction Manager John Reay. “The core drilling will provide confirmation. We might then consider filling any voids with lightweight concrete to remove any doubt, as we have elsewhere.”

Without ceremony

This is one of those low- key ventures that are easy to overlook. It has no background noise; only the clank of scaffold tubes disturbs the skylarks, or occasional bursts from the grinder. There’s something very appealing about it. But don’t let the atmosphere mislead you – there is a tangible output. Behind the debris netting, labourers are re-engineering the brickwork to secure the flow of potash. It’s what the railway does, without a fanfare.

Photos courtesy of Four By Three

Graeme Bickerdike
Graeme Bickerdikehttp://www.railengineer.co.uk

SPECIALIST AREAS
Tunnels and bridges, historic structures and construction techniques, railway safety


Graeme Bickerdike's association with the railway industry goes back to the mid-nineties when he was contracted to produce safety awareness videos and printed materials aimed at the on-track community. This led to him heading a stream of work to improve the way safety rules are communicated and understood - ultimately simplifying them - for which he received the IRSE’s Wing Award for Safety in 2007.

In 2005, Graeme launched a website to catalogue and celebrate some of the more notable disused railway structures which still grace Britain’s landscape. Several hundred have since had their history researched and a photographic record captured. A particular focus has been the construction methods adopted by Victorian engineers and contractors; as a result, the site has become a useful resource for those with asset management responsibilities.

Graeme has been writing for Rail Engineer for the past ten years, generally looking at civil engineering projects and associated issues. He has a deep appreciation of the difficulties involved in building tunnels and viaducts through the 19th Century, a trait which is often reflected in his stories.

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