Let’s set the scene. The rain was stair-rodding it and the wind was at gale force. The normally majestic backdrop of Pen-y-Ghent was lost somewhere in the grey murk and the land surrounding the work site was standing in water.
‘Go and get me some good pictures of the new sidings project at Helwith Bridge,’ the Production Editor had said … ‘And make sure it’s sunny!’
Well, what did he really expect? This was the Settle and Carlisle line after all!
Wind and water or not, the construction activity continued unabated. These seasonably dampened works were part of a £6 million scheme to once again connect Tarmac’s Arcow quarry near Horton-in-Ribblesdale with the national rail network. Funded by Tarmac Holdings Ltd, the scheme has been managed by Network Rail, with design and implementation work being awarded to Story Contracting (civils and track work) and Babcock Rail (signalling).
Arcow and its near-neighbour Dry Rigg quarry, both owned by Tarmac, have been worked under various ownerships for more than a century and there was a previous rail connection here. The then Ribblesdale Lime Company’s extensive sidings were controlled by the adjacent Helwith Bridge signal box. Closure of the sidings and signal box came in 1969 and road haulage has been in operation since then. Now, as you read this article, GB Railfreight is set to haul the first trainload of road stone out of Arcow quarry in fifty years.
Earthworks
Providing the new rail connection has been no small achievement. To all intents and purposes, a 750-yard stretch of entirely new railway has been built, ending in a siding fan within the Arcow quarry stocking ground. Indeed, this new line even has its own Engineering Line Reference – AQL (Arcow Quarry Line).
The previous sidings formation was deemed unsuitable for today’s requirements, particularly with regard to the curvature of the approach track. A new trailing connection has therefore been made with the Settle and Carlisle line, about 400 yards north of the old connection.
The new approach track leaves the Down main line on a falling gradient of 1 in 100, runs parallel with it for a short distance and then curves away across boggy agricultural land. In doing so, it is carried on a new embankment that reaches a maximum height of 3.5 metres before it meets the 20-metre high screening bund at the south end of the quarry site.
Constructed 25 years ago to satisfy Yorkshire Dales National Park (YDNP) planning conditions, the screening bund is built on a truly massive scale. Cutting a V-notch through it for the new railway has required the removal of 60,000 tonnes of material. Although unsuitable for use on the embankment, the excavated quarry waste has nevertheless been put to good use within the quarry site to form new roadways.
Raising the new embankment has required 26,000 tonnes of material that, in order to minimise transportation, was sourced entirely from within the quarry. The earthwork design was therefore tailored to suit this available material. Of all the rock materials used, only the track ballast, sourced from Shap quarry, had to be transported to site.
Settled
Not surprisingly, the construction of a substantial embankment over soft ground can present some problems. George Stephenson achieved success at Chat Moss by ‘floating’ his railway on bound bundles of heather and brushwood. But, taking a more modern approach, the solution adopted at Arcow quarry has been to surcharge the earthwork with additional material in order to hasten the settlement process. The technique used was more sophisticated than just depositing lots of material and hoping for the best, as Chris Sidwell, project manager for Story Contracting, outlined.
“We needed to avoid slippage and rotation at the embankment toe, which could occur if we added material too quickly,” Chris explained. “Although a geogrid was incorporated into the base of the embankment to provide stability, a crucial factor was the height of the water table. As material was added to the embankment, the increased downward force produced an increase in the ground water pressure, causing the water table to rise. It was this that could destabilise the embankment.
“Accurate measurement of the ground water pressure was vital. The technique, provided for us by Central Alliance, involved drilling boreholes down to between four and seven metres below ground level. Vibrating wire piezometers were lowered into the holes to the level of the natural water table, where they were then encased in sand cells.”
These devices have a flexible diaphragm that responds to external pressure changes. A wire attached to the diaphragm is tensioned and can be made to resonate by an electrical coil. The resonant frequency of the wire can be measured. In other words, the resonant frequency of the wire changes in sympathy with the external pressure acting on the sensor. The pressure measurements at Arcow were recorded by data loggers at three-minute intervals to produce a plot of pressure against time.
Chris continued: “As the embankment material was added and compacted, we could see a sharp rise in the water table pressure, which then gradually subsided.
When the pressure slowly returned to its former level we knew we could safely add more material. Thus the ground water pressure, and therefore water table level, when plotted against time, formed a characteristic saw tooth graph.”
The eventual objective was to add about one metre of additional material to the embankment, which was then allowed to settle for 28 days. During this time, the embankment level dropped by approximately 0.1 metres, with the rate of settlement decreasing as time passed. By studying the characteristics of this phase in the settlement process, the level of the embankment, with its surcharge of material removed, could be predicted into the future. When the ongoing settlement rate was known to be within manageable limits, the track could be laid.
During the embankment forming process, the level of the settlement was measured by means of rod and plate markers, the plate being installed at the original ground level. Future settlement at rail level will be monitored for some time by means of surface settlement markers fitted at cess level.
Deadline
The scheme project manager for Network Rail was Joelle Caldarelli, who was pleased to point out that the project had progressed from the planning stage to completion in a little over a year. “Physical work started on site in the summer, with the project time working towards the critical milestone of a 78-hour line closure, scheduled to take place between 23 and 27 October. As it was, to the great credit of Story Contracting and Babcock Rail, the vital preparatory works were completed one week ahead of that schedule.” The crucial blockade was necessary for the switches and crossings to be installed at the tie in.
Another aspect of the project that Joelle is happy with is the footbridge that carries a public footpath across the access line adjacent to the quarry bund. She explained: “At just the right moment, a lattice footbridge became available to us after its removal from a site in Camden.” Following complete refurbishment, the bridge, which has an eight metre span, was installed onto stone-faced abutments and now provides an excellent vantage point from which to view the sidings. “It’s nice to be able to reuse a beautiful piece of Victorian engineering in this way,” said Joelle.
But the project wasn’t without its challenges, with one issue being the discovery of Great Crested Newts. These protected, but seemingly omnipresent, amphibians were found to inhabit a natural dewpond adjacent to the route of the access line. Bowland Ecology installed newt fencing around the work site and a temporary dewpond was created nearby to relocate the captured amphibians. The newts will be returned to their original pond upon final completion of the landscaping.
Value
Within the quarry site, no substantial earthworks were required. The development has two sidings and a 135 metre long loading ramp has been constructed adjacent to siding number 1. YDNP planning conditions have dictated that a dust suppression facility should be provided. Water misting stanchions have therefore been installed between sidings 1 and 2. The water misting starts automatically when the presence of a front-loading shovel is detected.
Planning restrictions also limit the operating hours of both the Arcow and Dry Rigg quarries and restrict the maximum number of trains leaving the quarry to five per week.
Aggregate from Dry Rigg quarry will be hauled the short distance to Arcow quarry by road for onward transportation by rail. Each quarry produces road stone that is nationally important. It is a form of grit stone that has a high PSV (polished stone value), which makes it suitable for use on motorways, either as coated stone (within asphalt) or as a top dressing. The properties of the Arcow and Dry Rigg products are slightly different, so the two materials will be transported in separate rail wagons.
Each siding is able to accommodate up to eight 75-tonne wagons, so initially the maximum train weight will be 1,200-tonnes. It is estimated that this will remove 16,000 lorry journeys each year from the Yorkshire Dales National Park.
Signals
GB Railfreight will haul these loads using Class 66 locomotives and VTG-leased HYA bottom- discharging bogie hopper wagons. The destinations will be Hunslet East, Agecroft and Bredbury. The Arcow sidings connect with the Down (northbound) line, meaning that all trains will travel to Blea Moor before heading south.
To allow the locomotive to run round at Blea Moor, Babcock Rail has installed signalling enhancements there. It is now possible for Down trains to directly access the Up goods loop at Blea Moor. Previously this was not a signalled move.
Noticeable is the replacement of signal BM29, formally a running shunt signal, by a Dorman ‘lightweight’ three-aspect colour light signal, complete with position light junction indicator (feather), plus a ‘cats eyes’ subsidiary signal and route indicator.
The main line and trap points at Arcow are controlled from a local ground frame. Rather than clunking levers and point rodding, power operation has been favoured, making use of SPX Rail Systems in- bearer Clamp Locks. Control is from a shunter’s panel that is released from the lever frame at Settle Junction signal box.
Because the new points are located within an Intermediate Block Section that uses axle counters (issue 67, May 2010), and because of the need to shunt trains ‘inside’ at Arcow quarry, additional track circuits have been added into the axle counter section.
As part of the new signalling arrangements, Babcock Rail has needed to alter the mechanical lever frame interlocking at Settle Junction and Blea Moor signal boxes – something of a dying art these days.
Win-win
It’s a symptom of the times that many freight paths on the Settle and Carlisle route are now largely unfilled. Whereas once they were commonplace, you could wait a long time today to see a coal train breasting Ais Gill summit. Having a new freight flow on the line is therefore good news indeed and GB Railfreight was very pleased to sign a new contract with Tarmac.
The residents of Settle and the Dales aren’t arguing with this development either. Even though there are some planning restrictions on Tarmac’s operations at Arcow and Dry Rigg, transferring much of the aggregate output to rail will allow these quarries to operate at greater efficiency.
It’s hard to see a down side. Maybe we should all be singing along to Errol Brown’s classic hit, ‘Everyone’s A Winner.’ Come to think of it, some hot chocolate wouldn’t have gone amiss during our site visit!
Lead image: Story Contracting.
