The big push

BOB WRIGHT

The ongoing £1.2 billion East Coast Main Line (ECML) upgrade is made up of four major projects: the remodelling of the track and supporting infrastructure at King’s Cross to increase capacity, the Stevenage turnback (completed in 2020), power supply upgrades to the whole route and the Werrington grade separation.

The existing Werrington Junction layout, just north of Peterborough, constrains efforts to increasing the frequency of East Coast Main Line passenger services, as slow freight trains moving onto the Great Northern Great Eastern route (GNGE) need to cross over the two Fast and one Slow ECML lines.

As described in Rail Engineer (see Issue 181, Jan/Feb 2020), Network Rail considered dive-under and flyover options to separate the GNGE services from ECML traffic. But an overbridge was discounted as it would have been a substantial visual intrusion in the flat topography and would also have required diversion of the National Grid’s high-voltage transmission lines.

As an alternative to traditional ‘top down and open cut’ options, the chosen innovative solution - which minimised disruption to rail services - was a 750m radius, 155m long portal tunnel constructed alongside the ECML on the new dive-under’s alignment and then jacked into place. Over a nine-day partial closure of much of the ECML between 16-24th January, main contractor Morgan Sindall Infrastructure successfully installed the 11,000t concrete portal, the first time in the UK that a curved structure of this scale has been installed by jacking. Making sure The programme constraint here was the nine-day partial closure of the three ECML lines, which governed the planning and methodology for this project. Limited services continued using the Up and Down Stamford lines to bypass the works. PHOTO: NETWORK RAIL AIR OPERATIONS

Six days were allocated for the jacking into place of the portal tunnel structure, with permanent way, signalling and earthworks taking place before and after. Enormous effort went into ensuring the project could be completed on time. The team modelled numerous scenarios and mitigations to minimise risk and ensure contingency measures were in place. Trial jacking was carried out in December to test and prove the systems and method. At the completion of its installation, Network Rail East Coast route director Paul Rutter said: “Our teams have completed this challenging piece of engineering in a creative way, which also allowed a reduced train service to continue for those who still had to travel. I’m so proud that this project has shown itself to be one which is industry-leading and that our teams have had the opportunity to use this new technique for the first time in the UK on one of the country’s most famous railway lines.”

Design concept The tender stage design option produced by Network Rail was for a structure to be constructed in sections within a series of disruptive possessions. Morgan Sindall Infrastructure collaborated with Jacked Structures to produce an alternative proposal. Jacked Structures is a specialist engineering consultancy with unique experience of large jacked structures. Their alternative proposal was for a portal structure running on guide tracks located within preinstalled pilot tunnels, jacked into an open excavation created immediately ahead of it. This was based on their experience of the difficulties, risks and jacking of heavy loads involved in installing traditional box sections.

James Thomson of Jacked Structures holds patents for this method whilst Morgan Sindall

Infrastructure has a license to use it for the project. This alternative proposal was accepted.

Beginning in 2016, the two companies worked closely with Network Rail’s designers Mott MacDonald and Tony Gee & Partners to develop this unique structure, reflecting the topography, geology and time constraints. In addition to the tunnel itself, the two approaches required substantial retaining structures and soil nailing. The eastern approach also included a substantial reinforced concrete slab on which to construct the portal and provide restraint to the installation jacking forces. All aspects of the project have a 120-year design life.

(Below) An overview of the site. RECORD-BREAKING PORTAL JACKING ATWERRINGTON JUNCTION

(Right) Tunnel formwork within the contiguous piles retaining walls.

For this project, the tunnel was constructed on the eastern approach as a portal, with heavy-duty propping at 2/3 height - bracing the portal during installation - with the lower walls cantilevered from it. This concept greatly reduced jacking loads; omitting the floor both reduced weight and removed the high-base frictional loads, often a key consideration in jacked structures.

The slide path for installation was an L-shaped concrete structure. The portal was carried horizontally on multiple hydraulically-linked lift jacks and shoes running on lowfriction PTFE slide pads. For lateral guidance during installation around the curve, hydraulically-linked phosphor bronze pads bore against a vertically-positioned steel slide path on each side to keep the portal centralised and resist any out-ofbalance ground pressure on the side walls. There was a nominal 65mm clearance to each side.

The slide track beams formed within the guide tunnels bear directly on the very firm mudstone formation and act as strip foundations to the structure, until the in-situ base slab is constructed. Slide path tunnels

Two parallel tunnels - 168m long and 3.21m in diameter - were driven for the slide path beams. The Earth Pressure Balanced Tunnel Boring Machine was named ‘Chloe and Georgia Whiteman’ after the daughters of Mark Whiteman, a Morgan Sindall Infrastructure engineer working on the project who passed away unexpectedly in 2019.

The tunnels were 7m below the ECML and remote track monitoring was used to demonstrate no disturbance to the tracks above. The machine began work in February 2020, advancing 7m/day and finishing in August 2020.

Works were halted for three weeks at the outset of the Covid-19 national lockdown until appropriate working practices were devised, agreed and implemented. In addition, the site office and welfare arrangements were expanded at this time to provide more space for workers to be separated and to reflect the large number of people then working on site, and in preparation for the three 8-hour shifts during the installation.

Construction numbers

The north ramp was constructed within retaining structures, the first section consisting of a temporary retaining wall of contiguous 18m deep, 900mm diameter rotary-bored piled walls with steel overhead bracing. Beyond this, the formation passes through a steep-sided permanent cutting supported by 900 soil nails - each 8-10m long - and a sprayed concrete facing.

At the north end of the retaining walls, a pre-existing watercourse will cross beneath the trackbed through a pair of 1.8m diameter inverted syphon pipes within two 14m deep, 9m diameter shafts. The reinforced concrete reaction slab was 750mm thick, supported on 30 bored

PHOTO: MAMMOET PHOTO: BOB WRIGHT

(Left) The 11,000t portal in position for jacking, bearing on 28 skidding beams.

PHOTO: MAMMOET

piles, 1.2m in diameter. The slab included slide path beams to each side linking to those in the twin tunnels. There were also 34 rows of four jack-reaction pockets at 5.4m centres.

A 940m long ramp has been constructed to the south of the tunnel, between the ECML and the slewed Stamford lines. This also acted as the reception pit for recovery of the TBM. Piling for the south ramp consisted of 693 bored contiguous piles - up to 18m in length and 900mm in diameter - as well as 340m of 10-metre sheet piles.

Future drainage will be provided by pumping stations at each end, discharging into watercourses through attenuation features.

The 155m long, 9.5m wide, 5.1m high and 1m thick portal structure was constructed to a very high quality upon precast base units incorporating jacking and guidance pockets. Bell Formwork used Peri travelling formwork running on VTC tunnel carriages on guide rails.

Once completed, the structure received a spray-applied membrane to the top, with the sides being protected by bituminous waterproofing.

Jacking into place

The six-day jacking operation was undertaken by Mammoet on behalf of Morgan Sindall Infrastructure. The structure was lifted off the reaction slab onto skidding beams that ran on PTFE pads on the slide path. Calculations of worst-case scenarios determined a maximum jacking force of 3,600t might be required. The reaction slab and structure were designed around four installed jacks that could provide up to 5,000t.

Mammoet’s jacks are normally used vertically to raise offshore modules, but here were used horizontally. They were attached to the portal’s thrust slab, a section of floor slab between the portal feet, and their self-weight slung from a temporary overhead frame. The jacks bore against relocatable steel reaction frames set into pockets within the jacking slab and were extended in 2.7m strokes. 2.7m extension pieces were placed after a full jack stroke to enable a total length of 5.4m to be installed before moving the reaction system to the next available jacking pocket. 34 sets of four pockets were provided. Test jacking took place in December, using the first three sets, giving 13.5m of initial travel. The worst-case scenario assumed that the ground would slump against the sides of the portal as it was jacked through. In the event, the stiff ground did not slump and the maximum jacking force used was just 900t.

The jacking sequence was as follows: » Hydraulic crawler crane running on base slab, lifts in jack reaction frames into pockets in slab. » Hydraulic jacks push against these to move the portal forward by 2.7m. » Crane lifts in intermediate jack extension frames. » Hydraulic jacks push against these to move the portal forward by a further 2.7m. » At the front, side cutters fitted to the portal cut the ground profile and excavators cleared the earth for the portal to be pushed forward.

The cutter overbreak for this was just 50mm wider than the portal itself. The excavators also carefully broke open the tops of the two circular guide tunnels to reveal the two slide paths inside. » Spoil loaded and taken away by a fleet of dump trucks, in total approximately [16,000m3]. » Once the jacking was complete, pea gravel was poured between the portal and the excavation sides and subsequently further filled and sealed with cementitious grout.

(Right) The portal halfinstalled; the headwall will be at the far end of the overhead bracings.

The access shafts of the inverted syphon beside the temporary retaining walls.

The timeline of the nine-day partial closure was: » From 21:00, Friday 15th January: bidirectional signalling arrangements set up on Stamford lines and temporary works to

GNGE so that signalling was not affected when track removed. » Saturday 16th January: signalling taken out and disconnected, tracks removed and OLE lifted.

Bulk excavation and jacking began at 13:45. » Sunday-Thursday 17-21st January: bulk excavation continued throughout portal jacking. Push completed at 02:30 and jacks released at 22:00 on 21st January. » Friday 22-24th January: reinstate signalling, permanent way and

OLE. » 04:55 Saturday 25th January: handback in time for full passenger services to resume.

Over 24,000 hours were worked over the nine days, with no accidents or lost time. Completing the works

The project has already delivered substantial elements of permanent way, drainage, structures and other works, but much remains to be completed.

The floor slab inside the tunnel will be constructed tied into the side walls, becoming the ground-bearing element of the structure. This will include a vertical curve at the east end as the track alignment rises up through the cutting to form the north ramp.

Ballasting and installation of 8,000m of permanent way will follow. The junction with the GNGE tracks at the north end (Glinton Junction) will be installed in the autumn and with the Stamford lines at the south end in June.

The life-expired Werrington interlocking will be upgraded to a computer-based interlocking which will be carried out during a threeday possession in June, the same weekend at the King’s Cross commissioning works. The target approval of the new works by the Office of Rail and Road is at the end of October. The new junction will be reflected in the enhanced ECML services of the 2022 passenger timetable improvements, but is expected to be used by freight trains by November.

The long-term effects of Covid on rail travel are unknown, but the business case for this project was based on long-distance traffic which is less affected than shorter commuter journeys. The project will be a key component in increasing ECML capacity from six to eight long-distance high-speed services each hour.

This project has been a recordbreaking application of this patented method of constructing a diveunder and is one that may well be replicated by Network Rail in the future for similar projects where ground conditions are appropriate.

Journey’s end - the portal at the southern headwall position.

PHOTO: NETWORK RAIL

THE TIES

THAT BIND

GRAEME BICKERDIKE

(Right) The viaduct’s 108 pattress plates have been prepared and repainted, whilst 46 drainage hoppers have been replaced.

As we glide in 21st-century comfort along continuous welded rail - connected to social media and six billion web pages - it’s easy to forget that much of the infrastructure we’re travelling on, through or over is a product of Victorian grit. The busiest section of the West Coast main line is now 182 years old.

Trains are assembled, Meccano-like, in immaculate factories; half-a-mile of track can be renewed overnight by pushing buttons. It’s effortless, comparatively. But the grand structures that still circumvent landscape barriers were crafted by man’s hand in inconceivable circumstances. There was no task briefing or competence regime. There was no welfare cabin or weather-proof gear. There was no handrail or fall-restraint harness. There was no crawler crane or telehandler. There was no certainty that you’d see the end of your shift. Over the top

Arguably, the greatest triumph of our railwaybuilding exploits overcame the bleak terrain of the North Pennines to connect Settle with Carlisle, 73 miles away, via 20 viaducts (depending on your definition) and 7,000 yards of tunnel.

The line was born of the obstructive rivalry suffered by the Midland Railway at the hands of the London & North Western, whose line it relied upon for access northwards from Ingleton - a small Dales village where the two companies built stations at either end of a viaduct. Passengers faced a stiff walk from one to the other before an agreement eventually brought the coupling of the Midlands’ carriages to L&NWR services, often dawdling goods trains. It was no way to run a railway.

PHOTOS: FOUR BY THREE

In frustration, an independent route was surveyed and approved, but, as interest rates soared in a bank failure’s aftermath, the Midland petitioned Parliament for permission to abandon the scheme. Refusal prompted a start to construction in November 1868, with the venture set to cost £2.3 million - a snip at £237 million at today’s values.

Moorland suburbia

Batty Moss nestles beneath Yorkshire’s twin peaks of Ingleborough and Whernside. Horton-in-Ribblesdale is five miles distant, Ingleton six miles and Hawes ten. The middle of nowhere is thus defined. Curving elegantly across the bog for quarter-of-a-mile is a 24-span viaduct, now known universally as Ribblehead, reaching 104 feet skywards and 25 feet into the earth.

It was Grade II* listed in 1987, whilst the land to its east is designated as a scheduled ancient monument. Here, the navvy encampments of Belgravia and Sebastopol were intersected by a network of two-foot gauge tramways laid to benefit construction; two more - Inkerman and Batty Wife Hole - were found a stone’s throw further south.

The 1871 census records 900+ men employed on this section of line; the camps offered shelter to around 2,300 at peak times. Hereabouts were a hospital, post office, library, mission house, schools, shops and pubs, alongside the offices, stores, stables, quarries and brickworks that served the engineering activities. Insatiable appetite

When an adventurous correspondent journeyed here from London in October 1872, the viaduct’s southern approach embankment was well advanced and a bridge through it completed. Extraordinary scenes then took his breath away.

“A number of low, wooden huts, covered with tarred felting, have grouped themselves together without pretence to Cementitious grout is injected under pressure around Cintec anchors, installed at 12 locations along the structure.

Many of the navvies killed at Ribblehead are buried in the graveyard at nearby Chapel-le-Dale.

arrangement on either side of the road that winds down rather steeply from the archway to the little pool formed by the head waters of the Ribble, as they spring out of the limestone rock.”

This was Batty Wife Hole with its 74 dwellings, a settlement commemorating the legendary demise of a local woman whose husband - Mr Batty, who lived on the fells - did away with her in the ‘churn hole’ from which the stream emerges.

“Great square-shouldered rough-faced men, with slouched billycocks, knotted kerchiefs, very short moleskin trousers and tremendously stout ankle jacks, come lurching out the huts and stride heavily through the oozy moorland to the scene of their work.

“The navvy works hard - ten hours a day, and no lazy pottering when he is at work - and he insists upon living well, as he has indeed a right to do. He has his four meals a day, and meat with every meal. In one house in Inkerman, where there are eight navvy lodgers and a family besides, the consumption of butcher’s meat is over 100lbs a week.” Living on the edge

Our correspondent ventured up the tramway to behold the men’s industry. “The line is a temporary way which winds deviously across the hollow, already partly spanned by the huge skeleton viaduct. I scramble along somehow, through knee-deep bogs, on to piers whose foundations are just level with the surface, past batches of stone-hewers hammering away industriously at great blocks of blue stone for the piers of the viaduct; then I find myself amongst these, and in the labyrinthine scaffolding that encircles them - looking up at trucks and engines traversing tramroads at a dizzy height, at derricks and blocks, and pulleys, at noisy little fixed engines, and at silent busy masons.”

It’s thought that more than a hundred navvies succumbed here, through calamitous mishaps, smallpox outbreaks and conflicts fuelled by alcohol. They fought as hard as they worked. Church of England records indicate around 200 burials of men, women and children in the nearby graveyard at Chapelle-Dale; unmarked graves are thought to be scattered across the moor.

The price paid by those who gifted us our railway network against all odds is a debt we must never lose sight of.

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Back from the dead

A hundred wild winters took their toll on Ribblehead Viaduct, its masonry impacted by water ingress. Repairs were undertaken sporadically through the 1980s, with linespeed reduced to 20mph over a single track to centralise the loading. When British Rail proposed the route’s closure - citing the high maintenance burden of its major structures - the energetic Friends of the Settle-Carlisle Line was established to mobilise public opposition. Its reprieve came in 1989 and the viaduct underwent major refurbishment in the early Nineties, led by resident engineer Tony Freschini.

Today, the structure tells the story of its own evolution, with an assortment of metal fixtures, concrete quoins and red brickwork patches. It’s stood up well to the subsequent 30 winters, but another intervention is now underway, making good the defects that time inevitably perpetuates.

The remit was lodged with the Works Delivery team for Network Rail’s North West route a couple of years ago, resulting in examination reports being studied, site surveys undertaken and drawings produced. A base model for the viaduct was created from as-built records and a LiDAR resource covering the entire route, obviating the need for a specific topographical survey; however, using a drone, Commendium subsequently generated an impressive 3D scan of the viaduct, working alongside heritage consultancy firm Wardell Armstrong.

Site mobilisation got underway in October and saw the establishment of a compound on pre-existing hard-standing at the southeast corner of the viaduct. A no-dig haul road, comprising MoT Type 1 stone, was laid on a geotextile along its west side. Touching distance

The greatest challenges here arise from the structure’s location, scale and restrictions imposed due to its listed status. The cost of scaffolding every part of it would likely have exceeded the scheme’s £2.1 million budget; it was therefore decided to focus activity where the priority was highest, covering Spans 4, 9, 10, 12, Longitudinal fractures mid-span have been stitched, cleared out and repointed.

Surface Preparation Protective Coatings Sca old & Containment Rope Access Steel / Masonry Repairs Structure Refurbishment

Working throughout the UK with o ces at Rugeley, Sta s and Bishop Aukland, Co. Durham

Due to listed building constraints, the scaffolds could not be tied into the structure.

13, 14 and 18 (numbered from the south), the piers to both sides of those spans and an isolated pier between Spans 5 and 6. The sequencing would generally involve repairing one span whilst the scaffolding was erected for the next and dismantled at the last.

A condition of the listing building consent requires “the character, appearance and historic significance of the Ribblehead Viaduct” to be “retained and conserved”. In practical terms, this means that the repairs mustn’t visibly alter the structure in any material way whilst the temporary works have been non-invasive - so no tying into the masonry or excavating foundations.

To address these constraints, scaffold designers RDG Engineering specified aluminium tubes to reduce loading by about one-third. This brought manual handling benefits for the construction staff from QED Scaffolding, as well as reducing the number of deliveries from the firm’s depot in St Helens; it did, however, require the use of double standards (two vertical legs) to share the load. Scaffolding one span typically took 19 days.

Sitting 300 metres (984 feet) above sea level, the area around the viaduct is unsurprisingly prone to storm-force winds. Although the tubing could abut the stonework, there would remain a tendency for it to twist under wind loads of 1.16kN/m2 - double the typical value - so the scaffolds were stiffened by installing chains of plan bracing.

It’s a notable aside that Brian Eades, QED’s managing director, helped to facilitate the viaduct’s Nineties restoration - when the scaffolding stretched from one end to the other - and has been on site a couple of times a week throughout the current project.

Getting it right

You might regard this as housekeeping on a grand scale. The shopping list for remediation read as follows: remove vegetation and roots, rake and repoint open joints, stitch and grout fractures within the brickwork, insert concealed anchors, cut back and renew spalled masonry, and install stitching bars through cracked voussoirs. All of these solutions were mixed and matched, as required, to meet the needs of each span - getting on for 200 interventions in total. And throughout the structure, external metalwork was repainted and the water management system maintained.

Again, the imperative was to work sympathetically with the structure. The mortar specification of four parts quicklime to 11 parts Nosterfield sand and one part clinker - with the addition of a natural clay pozzalan to 10-15% of the volume - arose from laboratory analysis of ten

PHOTOS: FOUR BY THREE

PHOTOS: FOUR BY THREE

samples taken from three piers and two arches. Five different mortar types were discovered, from the original lime mortar to the Pozament used extensively for the Nineties refurbishment.

All this is indicative of the care and attention now demanded by planning authorities when working with heritage structures, particularly those with such iconic status. For example, the listed building consent required open joints to be raked out using hand tools before the colour-matched mortar was manually applied and hit with a stipple brush to consolidate it.

A happy consequence of this approach is that it avoids the introduction of stiffer local anomalies within a structure through the use of materials much stronger than the original. This was an unfortunate strategy in days gone by and, in the long term, often made matters worse. Many structures have thus suffered.

Pull yourself together

At Ribblehead, it can be observed that the tie bars inserted through each span either side of the crown seem generally to have prevented the voussoirs separating from the arch - an issue seen on many viaducts - but longitudinal fractures have appeared in the brickwork lower down towards the piers.

Resolving these has involved the stitching of reinforcement bars across fractures recorded mid-span - adopting a Network Rail standard detail repair - whilst, closer to the edges, around 80 Cintec anchors have been installed at 12 locations along the structure. These are stainless steel bars in woven polyester sleeves, into which a cementitious grout is injected under pressure. The sleeve restrains the flow and expands to about twice its normal diameter, moulding itself into any spaces within the brickwork to provide a mechanical bond, thus dispensing with the need for pattress plates.

Holemasters have undertaken the drilling works. Beyond the obvious access difficulties of getting water barrels, power and tools to the required height, their staff had to contend with a prohibition around the mounting of rigs onto the structure. Instead, each three-metre-long core - 40mm in diameter - had to be hand-drilled horizontally using an assortment of bits and extensions, through the voussoirs and into the arches’ five brick rings. Once the anchor was installed, the repair was rendered invisible by grouting the outermost 50mm from the core back into the hole as a plug.

Ben Campbell, Network Rail’s programme manager, makes a couple of crucial and intriguing observations at this point The viaduct’s 108 pattress plates have been prepared and repainted, whilst 46 drainage hoppers have been replaced.

Cintec continues to serve Network Rail with tested and proven structural solutions as it has the last 35 years.

PHOTO: FOUR BY THREE

PHOTO: MATT KIRBY

The 24-span structure across Batty Moss extends for quarter of a mile and reaches a height of 104 feet.

about hidden critical elements. Firstly, they highlight the importance of effective records management - and the need to consult those records - to ensure we don’t forget they’re there.

Secondly, Ribblehead’s tie bars were installed decades ago, though precisely when we don’t know. “What condition are they in? How corroded are they?” he asks. “They’re inside a structure that’s largely waterproofed, but we’re having to assume they’re still good. Can we do some form of in-situ non-destructive testing of tie bars to see whether they’re intact across their whole length? It’s a risk for the railway industry and something worth looking at.” Finishing touches

Hanging over the parapets throughout my visit were ropeaccess specialists engaged by Industrial Coating Services (ICS), supported by Teesside Industrial Services. Secured to one-tonne kentledge blocks placed trackside during possessions, these high-flyers were wielding needle guns and grindettes to mechanically prepare some of the 108 pattress plates which were subsequently cleaned and repainted, along with a further 360 pieces of exposed steelwork. ICS’ contract for this part of the scheme included the replacement of 46 drainage hoppers and painting the associated downpipes.

Specified was a winter-cure system from Jotun involving primer and intermediate coats - suitable for application at temperatures below 5°C - and a gloss finish coat which requires warmer conditions, not often experienced here over the wintertime. The system offers a 15-year lifespan. To minimise potential disruption from high winds, the team set up for work on both sides of the viaduct so there was always a sheltered side available.

The hardy explorers who pass beneath Ribblehead Viaduct before climbing up Whernside will see nothing of these labours once the scaffolds are gone and cabins removed. That’s the point, of course - the heritage regulators demanded seamless engineering here. But you can’t change history. Up close, the structure’s hodgepodge appearance reflects the railway’s efforts to stave off the impacts of 145 years’ weather and traffic loading. Step back though and a peculiar harmony reveals itself: this monumental feat remains very much at home in an often hostile landscape.

With thanks to Ben Campbell, Andrew Walker, Ian Ross, Samantha Mikhail, James Marlor, Richard Parker and the on-site team for their help in producing this article.