We do things very differently nowadays. Mechanical and technological evolution – not to mention health and safety – has completely rewritten the railway engineering text books since the Victorians first filled them with pioneering insight. Writes Graeme Bickerdike
It was a primitive business back then, relying upon man’s courage and ferocity assisted by horses, explosives, hand tools and the musings of Archimedes. Machinery didn’t really make its presence felt until the 1870s, by which time the core railway network had already been forged. And when it subsequently came to maintenance, the extent to which safety played second fiddle to performance would today make even the most audacious engineer’s toes curl.
Witness the early life of Cwmcerwyn Tunnel, 1,012 yards in length and host to summit level on the Port Talbot Railway which meandered through the Llynvi, Garw and Dyffryn valleys in search of coal to export. Opened in 1897 after 18 months exertion, its contractors encountered mixed strata as they cut through the hill, so construction methodology varied also. In some places sidewalls were dispensed with but elsewhere inverts had to be installed. Ground movement was apparent from the outset, distorting the lining by as much as 20 inches. Strengthening work was programmed in 1898 and 1902, adding concrete inverts and heavy timber struts at the toe of the sidewalls. But the gradual crushing of the arch continued, prompting the decision to reconstruct 60 yards of tunnel in 1908.
Cwmcerwyn was not generously proportioned, built only for a single track. And yet one overriding priority came down from on high: traffic must not be disrupted. So the successful tenderers, Messrs Perry & Co, developed a mobile canopy to separate the trains from the workforce as they hacked away brickwork and fitted cast iron segments in 20-inch wide rings. The canopy, 12 feet in length, provided a 4-inch clearance around maximum loading gauge whilst the poor souls outside it laboured in a space less than three feet wide.
Loaded mineral trains stopped in the tunnel whilst a crew member pinned the brakes down in preparation for the long 1:40 descent from the west portal. This resulted in the tunnel being filled with choking smoke for as long as 20 minutes, rendering work impossible until it cleared. Yet despite this impediment, progress wasmadeatarateoffiverings-or8feet4inches-per week. The job was substantively finished in six months, without hardhats or injury.
Hit the ground running
A century and 160 miles away in Lancashire, Network Rail faces a similar challenge on the Copy Pit route between Hall Royd Junction – east of Todmorden on the Caldervale line – and Gannow Junction where the Colne branch converges. Since 9 November last year, replacement buses have been ferrying passengers over the hill between Burnley Manchester Road and Hebden Bridge/Todmorden stations while engineers complete a programme of remedial works at Holme Tunnel which will see the structure partly repaired, partly rebuilt.
The project’s whys and wherefores were examined in Issue 109 of The Rail Engineer (November 2013), but it’s worth reminding ourselves briefly of the background. Opened in 1849, the 265-yard tunnel penetrates a spur of land below Thieveley Scout, part of the ridge that forms the south-west side of the Cliviger Valley. Several rotational landslips have occurred here resulting in unstable ground.Since the 1970s, an increasing number of defects have been recorded in the tunnel, with the situation at the south (Todmorden) end becoming sufficiently serious to warrant the installation of 152 steel ribs between 1986 and 1991. However the degradation continued to a point where the Up-side haunch was displaced by as much as 320mm, forcing the crown upwards by 180mm. Loss of gauge clearance led to the introduction of a 20mph PSR. In terms of long-term performance, it’s not difficult to understand Network Rail’s motivation in restoring the tunnel’s structural integrity through the current intervention.Eighteen months in the planning, the physical works got underway over the summer of 2013 with a series of possessions taken to inject grout behind the lining, improving the strength and cohesion of the ground. This proved a significant task – consuming around 450,000 litres of grout – but it contributed to the safe breaking out of the existing brickwork. Alongside this, 87 new steel arches were being fabricated by Barnshaws in Wolverhampton whilst Hanson, from Derby, manufactured the accompanying concrete inverts. These elements form part of the design, developed by Donaldson Associates, for the reconstruction of the lining at the south end.
The project team moved onto site in May after Network Rail acquired a parcel of agricultural land alongside the railway to serve as a compound and access point. These will be retained for maintenance purposes once the work here is done; the existing facilities 150 yards down the line are limited for space.
Amco Rail is fulfilling the role of design and build contractor. Critically they bring with them years of experience in the mining industry. For the 20 weeks of the blockade, the tunnel is effectively an oversized colliery roadway; forget the fact that trains will soon be running through it. The solution being applied here is known in the trade as a back-rip, a technique that’s been used below ground for hundreds of years.
What strikes you most when venturing through the south portal is the intrusive and brutal nature of the work. That, and the determination. The section being rebuilt extends 87 metres in from the Todmorden end. Immediately apparent is the change in profile between the old displaced steelwork in the foreground and the 52 new arches that had previously been installed beyond. It’s an image that tells you much about the forces exerted on the lining over its lifetime.
The operation is cyclical, ongoing around the clock to meet a tight programme. The methodology has evolved a little through experience, with previously sequential activities now taking place concurrently. In overview it involves the withdrawal of four existing arches together with the associated cess casings and invert. A 1.5 metre section of lining – which was pre-cut at the start of the blockade – is removed, the ground trimmed and rockfall protection mesh fitted. Precast concrete invert units are then laid and angled steelwork bolted to it to support the arches which come in three sections, connected by flexible temporary joints. An excavator fitted with a bespoke attachment lifts them into place. The sequence is repeated until 12 metres has been completed, after which the invert and cesses are poured and a 420mm lining sprayed using fibre- reinforced concrete.
While the theory sounds neat and tidy when condensed into five sentences, reality brings variables with it – and therein lies the challenge. That’s why this project is not being driven by railwaymen or civil engineers; the Network Rail team has stepped back a little and placed its faith in Amco, an approach that pays dividends for both. They regard theirs as probably the best client/ contractor relationship either has ever encountered. That’s some assertion. Peter Shrader, Network Rail’s senior construction manager, tells me that “Your headline will be ‘Collaborative working delivers success!’” It’s better in the body text, Pete, but the truth behind that sentiment is apparent to even the casual visitor. When an ORR inspector appeared before Christmas, his feedback read “If we could bottle what’s happening here, I’d be out of a job.”
Big bang theory
The ground here changes yard by yard. “When we first set off back in November we had perfect conditions,” recalls Amco’s project manager Dave Thomas. “We thought we’d won the lottery.” The compressive forces of the ground movement had been such that, even when the brickwork was removed, the formerly-broken material behind it held in a perfect arch.
But it was always expected that things would deteriorate as they retreated towards the portal. A number of roof falls have occurred including one just before Christmas of more than 100 cubic metres. To ensure complacency never creeps in, the release of stored energy in the ground can suddenly launch large pieces of stone across the tunnel. You can see then why Amco’s Keith John, in the weeks before the blockade, spent time on the road looking for the right men: familiar, trusted faces in established gangs who travel the country from job to job.
There’s something unique about miners as anyone who grew up amongst them – as I did in West Yorkshire – will testify. The nature of their shared experiences strongly binds them together and this works to everyone’s advantage. There are two teams of six here, mostly with roots in South Wales. They change shifts at 07:00 and 19:00 but their commitment extends beyond those booked times. Supporting them are 20 skilled operatives per shift, bringing materials in and taking debris out. Their role is to ensure that the back-rip never stops.
Dealing with roof falls follows a set procedure: clear away the debris, spray in concrete to cork the ground, set the arch ring, shutter off the void and pump expanding foam into it. A resin is then injected to compress the foam, effectively preventing the ground from breathing. All this eats into the schedule by about two days on each occasion. To strengthen the ground adjacent to the Up sidewall and thus provide more support to the shoulder, a recent addition to the operation has involved the localised injection of Wilkit resin – a silicate-based system that sets to form a compact grout. It’s expensive but promises long-term benefits. This activity has been taking place on weekend nights so as not to interfere with the main works.
Muck gives way to water as you move beyond the heavy industry of the rebuild. That familiar tunnel drip- drip-drip provides the day shift with an assortment of maintenance and remedial tasks. Amongst these is the installation of cess drainage, tied into the new six-foot drain, to collect water as it runs down the lining. Through this section, the issue is fracturing of the brickwork rather than lateral movement so extensive recasing is apparent – rather more than was initially anticipated.
The north (Burnley) portal has been repointed and de-veged ahead of drainage being installed above the headwall. The more intrusive works are at the other end where the Todmorden portal has been completely dismantled to allow its reconstruction in concrete. This will be refaced with the original masonry. Behind it, the hill has been raked back slightly and trees removed to allow a new drainage system to be put in. There is then a 650 metre track relay to be delivered by Stobart Rail before trains start to run again on 24 March and the PSR finally disappears.
Sooner or later, whether it takes months or decades, nature will attempt to reclaim what the railway has taken from her by driving its tunnels. Cwmcerwyn was under pressure from the outset; Holme proved more resilient but eventually succumbed. However, Network Rail and Amco are ensuring that the Copy Pit route will not suffer the same fate as the Port Talbot Railway which saw its last traffic in 1964. Key to their success in difficult circumstances has been a partnership approach. As they prepare to move onto their next projects, Dave reflects “It’s a shame it’s got to end!” Hopefully they’ll take the same spirit with them.