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Harringworth Viaduct – Travel & Repeat

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As nineteenth-century railway companies levelled corridors through Britain’s landscape, those in their employ inflicted disorder and upheaval on the places they visited. Navvies earned notoriety for working hard and drinking even harder, that latter characteristic having a predictable impact on previously unsullied rural communities.

There is, however, a more nuanced story to tell. Of immense social value is the Reverend Daniel William Barrett’s sympathetic insight into navvy culture, chronicled during his time running a Railway Mission on the Kettering-Manton line in the late 1870s.

Seaton, a village close to the Rutland/Northamptonshire border, had a population of about 320 at this time; then Messrs Lucas & Aird arrived with their construction contract from the Midland Railway. Suddenly, 47 wooden huts appeared nearby, at the northern end of a proposed viaduct; each one typically housed seven men, two women and three children – upwards of 560 souls. Beer consumption was conservatively estimated at 30 gallons weekly per hut (a daily rate of about five pints per man), on top of which was half a gallon of whisky.

But the work ethic was heroic. Wagons with a capacity of 2¼ cubic yards would do 14 rounds in a shift, with two men allocated to each one. This meant that every man was tasked with shovelling more than 20 tons of earth, above their heads, in 12 hours. And they often finished early. At its peak, a workforce of 3,500 – assisted by 120 horses – was occupied along 15 miles of route. Around 90 million bricks had to be manufactured and fired, mostly on site. It was backbreaking, monotonous and monumental; today, it is also beyond anyone’s imagination.

Hard sell

Using three kilns, Mr R Holmes made 20 million bricks for the line’s centrepiece – the aforementioned viaduct across the Welland valley and its flood plain, now generally taking the name Harringworth. Extending for 1,280 yards (1,171 metres), the structure was surpassed in length only by the elevated multi-track approach to London Bridge. Responsible for its design was the firm of consulting engineer William Henry Barlow, his second son Crawford – who acted as resident engineer – and former pupil Charles Bernard Baker.

A banquet to celebrate the keying of the last span by Lieutenant Colonel Tryon – whose land the viaduct stood on – was hosted in a shed at Seaton station. It was July 1878 and work to construct the 82 arches had been ongoing for less than 13 months. Barlow Jnr described the structure as “one of the grandest and most perfect pieces of workmanship to be seen in the United Kingdom”. History suggests he was probably overdoing it, but he had every right to indulge in a little hyperbole.

Strong and stable

Throughout its operational life, Harringworth Viaduct has benefited from numerous repair interventions, hence its red and blue patchwork appearance. The most recent, undertaken by Amco Rail for Network Rail’s Infrastructure Projects East Midlands Civils Renewals team, was extensive and deeply described by Chris Parker in August 2016’s Rail Engineer.

In summary, the work has involved a comprehensive programme to address all recorded brickwork defects, together with optioneering for a longer-term strengthening scheme which will raise the structure’s currently-restricted load capacity rating to RA10. As things stand, 25-tonne axle-load freight is limited to 20mph across the viaduct; the objective is to increase this to 60mph. However, the need for further option development has prompted the deferral of this phase into CP6.

We return now to focus on the parapets, which presented a challenge that could not reasonably have been overcome by conventional means – a bespoke machine was called for.

Better connected

Investigations by Cowi UK (formerly Donaldson Associates) indicated that the transverse distribution of live load through the viaduct’s fill material had the effect of pushing out the spandrels, driving arch ring separation as well as the formation of longitudinal cracks in the arch barrels below both the six-foot and inner face of the spandrel walls. These were, in turn, causing the parapets to lean outwards, whilst movement of the piers and arches under traffic – combined with an absence of construction joints in the parapets – encouraged extensive fracturing to occur. Whilst none of this is unusual in masonry structures, the lean was locally significant – recorded at more than 40mm.

Cowi’s remediation design – developed by senior engineer Manesha Pieris and Peter Harris, director of civil engineering – specified the local replacement of bricks and installation of 6mm-diameter stitch bars within the mortar joints across the vertical cracks. To better secure the parapets into the structure, it was also decided to grout 20mm-diameter vertical reinforcement bars at one-metre centres through the brickwork along the full length of the viaduct, a total of more than 2,300. Every third bar was 1,400mm long to reach the dentil corbels below the stone string course, the others were 1,200mm.

Thereafter, 20mm joints would be saw-cut through the parapets – two each side per span – to allow some shear movement, thus reducing the likelihood of cracks reappearing. To lessen their visual impact on the Grade II listed structure, the joints would be located alongside thickened sections of brickwork on the outer face of the parapets, symmetrically above each arch.

On the inner face, galvanised steel angle brackets would be fixed either side of each joint, extending down from the coping stones into the stepped lower part of the wall where it would be inset. A complication here was the presence of a troughing route at the toe of the parapet on the Up side, which had to be temporarily relocated. The brackets were also used at locations where the lean exceeded 40mm, making a total of 716 to fit across the structure.

First seed

Confronted with the considerable task of delivering the design was Amco’s project manager Shaun Trickett. He approached specialist drilling contractors who took the view that three teams could probably achieve sixty 27mm-diameter cores in an eight-hour shift using DD400 rigs. To complete, approximately twenty-six 16-hour possessions would be needed, with a steep emerging cost of about £500,000. But this ‘traditional’ approach brought issues around working at height, HAV (hand-arm vibration) and the risk of the core breaking within the brickwork or pushing it over. The search immediately got underway for a better system.

Together, Shaun and John Keele, Amco’s plant manager, came up with a concept for a rig which would sit over the parapet. It was based around three MBS piston drills – hardware with a long track-record in the mining industry for the likes of rock bolting. Working in collaboration with Network Rail’s own project management team, an on-site test took place involving a single drill held by a quick-hitch and eight-tonne mini excavator. This proved the starting point for a year-long process of development and refinement led by Chris Scott at Foulstone Forge.

As Rail Engineer has previously reported, Chris is a problem-solver, using hydraulics, pneumatics and ingenuity to achieve what was not hitherto practical, or to do so more efficiently. Whilst the level of complexity varies from machine to machine, his attention to detail is always absolute. On this occasion, he proceeded to explain Charles’ Law, describing why the air-flushed drill bits are cool when withdrawn.

Hang in the balance

Weighing 900kg, the rig comprises a three-sided frame which hooks over the parapet, lifted on and off by a roadrailer but entirely independent in terms of stability. It sits on durable high-grip rubber wheels, adjustable in height to ensure the drills remain vertical despite the slope of the coping stones. Powering the front pair is a 3kW traction unit with an epicyclic gearbox, enabling the rig to self-advance between the refuges, located over every third pier. Guide wheels are provided on both side pieces, running along the copers’ upright faces and a string course. The position of the wheels can be set from a place of safety using a lever and pin system.

Used to drill the holes are three Turbo Bolters, supplied by Minova, each one being mounted to a crosshead which travels freely up and down a vertical post, driven by a double-acting pneumatic ram with a pulling pressure limited to 40psi – sufficient for effective drilling but not enough to unintentionally lift the rig off the parapet. Despite much of the kit being outboard, the whole system will rest securely on the copers without any lateral restraint thanks to two counterbalancing legs on the inboard side.

Behind the RRV are two T8 trailers. On the first is a 4kW vacuum unit – to capture the expelled drill cuttings – standing alongside a panel from which the works supervisor can individually control the drills, their travel mechanisms and air flush. There’s also a ‘dead man’s handle’ which shuts everything off if mishap results in its release. Ancillary equipment is carried on the second trailer, notably the 500cfm compressor for the air supply, as well as lighting and a generator.

Bit by bit

On-site operations were logistically hampered by the nearest RRAPs (Road Rail Access Points) being six miles away at Corby and Manton. This meant that two hours were lost at the start and end of each possession due to the required set-up and travelling time, although this was later halved when permission was granted to stable the RRV and trailers on the ACE siding at Manton, leaving all the equipment permanently rigged.

Initially, 25 possessions were arranged, most of them running from midnight on Saturday to 16:00 Sunday. Day and night shifts were established, overseen by foremen Tommy Johnstone and Colin Turner, whilst Paul Thompson and Lee Kaszar – who were already familiar with MBS drills from their previous careers down the mines – underwent training at Foulstone Forge to become licenced operators of the system.

On the rig’s first outing, the team achieved 120 holes in a six-hour shift and maintained this rate thereafter. When Rail Engineer attended, one ‘travel and drill’ cycle was typically being completed in three-and-a-half minutes, the grouting-in of the bars following on immediately behind. Despite the use of Minova polycrystalline diamond-tipped bits, the make-up of the wall proved a significant variable, with soft red brick, hard blue brick and 5mm-thick steel plates encountered. Over one particularly tough weekend, the team went through 60 bits.

Speculate to accumulate

The brick-laden drudgery of Harringworth Viaduct’s construction period presents a harsh contrast with the comparatively seamless hole-drilling exercise progressed by Amco 140 years later. The former was delivered substantially by hand, many hundreds in number; nowadays these wearisome and repetitive tasks can be done by finger, pushing a button or pressing a lever. That’s how it should be, of course, greatly reducing the attendant risks.

But there is another bonus here, measured in time and money. By investing £60,000 in the rig, an overall saving was made of around £200,000; the drilling was finished several weekends early, such was the improved efficiency. And by adapting the rig to fit other parapets – a fairly modest job – there remains the potential to reduce future project costs elsewhere. It might be uniquely spectacular, but Harringworth Viaduct is not alone in suffering problems with middle-age spread. There will be more to come.

Photography: Four by Three

Written by Graeme Bickerdike


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