But there are drawbacks, not least the wind that whips spray in from the Irish Sea splattering the line with sand and salt spray. It has taken a heavy toll on the ironwork and brick of the half kilometre long multi-span Leven viaduct – one of several estuary crossings on the line.
Major repairs in 1915, and again in the 1950s, strengthened the bridge but age had brought it near to closure. The Cumbria Coast Line remains important for tourist and local traffic, but is also a key part of the Trans Pennine express link, linking into main lines at Lancaster. It is also used for important freight transport, most critically nuclear waste movements to and from the Sellafield reprocessing facility further around the coast.
Therefore, owner Network Rail put just over £14m (nearly Euros 21m) into a complete rebuild of the viaduct, ripping out and replacing the old deck and tracks along all 49 spans.
Work started in March and there was just four months for Carillion Engineering Services to complete the project. Easier said than done. The long cramped site was potentially a logistical nightmare. Fortunately, both ends of the bridge could be accessed with machines and materials from depots along the track at either end, said Carillion’s contract engineer on the project Matthew Wyld.
Network Rail’s original conception was that the work would need two seasons to complete, working on one track at a time and using the other to move in and out of site, explained the client’s project manager Neil Jones. Blockades of 16 weeks were prepared for the spring this year and next, when the weather was most likely to be favourable.
But, Carillion’s design and build tender proposed a faster system to concentrate all the work into the same season, said Jones. The speed-up came from using two specially commissioned overhead lifting gantries rather than on-track cranes, for lifting out old sections and later putting in the new. It was still done along one track first and then the other – but all in one possession. “We were able to do some other work on the track further along taking advantage of the blockade and eliminated 2007 closures,” added Jones.
The bridge work involved cutting out the track and its support on each side. The old configuration comprised primarily longitudinal steel girders, six in all with cross connecting angle pieces and then secondary angle pieces running longitudinally, said Jones.
“This supports a variety of deck plates, some the original wrought iron but as you can imagine this is often like lace and in many places has been replaced with cross timbers or newer iron plates,” he added.
Above, the bullhead rails were mounted on longitudinal timbers that run along the main support girders. Typically, the spans crossed this way are between 9 and 12m long, although there are a few shorter 7m spans and one central and navigable span is longer at 20m.
To use gantries required something to support them and so Carillion designed a scheme involving special rails running down either side of the track on newly installed walkways. The walkways were anyway part of the upgraded finished crossing for future maintenance access, replacing original maintenance paths which sit too close to trains for modern safety requirements – within 1.25m of tracks, in fact. The new one sits further out.
A system of sleepers welded into units was temporarily installed on top of the new walkway and two portal frame gantries ran down special 150mm by 150mm box sections on the top. Carillion put out its concept to tender which was won by specialist maker Abnormal Load Engineering (ALE) with a slight modification of the CES design.
The units comprised a portal frame at each end spanning approximately 8m from walkway to walkway, and connected with two longitudinal beams which created a long span of 9.5m – enough to cater for the pier-to-pier distance on most of the viaduct.
Lifting was carried out by chain hoists mounted on a control and machine platform on the top connecting beams, each 25t in capacity but with a total of around 40t when the load was shared below on a distribution beam. That was enough for a single track section of the new deck to be lifted in.
The hoists were “similar to strand jacks but working with chains,” explained Peter Schoenmakers, the ALE project design engineer for the scheme. They were ALE’s own design and used a hydraulic ram at the top gripping the chain over a 350mm stroke and then releasing it onto lower locking grips before repeating the stroke.
To move a load sideways the top platform sat on a Teflon skid arrangement on the top of the portal frames, so that sections could be lifted onto trucks below on the other track.
For the work itself, the railway track was first cleaned and prepared and scaffolding and safety guards installed. “There was a cascade of work along the bridge,” said Wyld, “which is similar to a production line sequence. The logistics of it had to be very carefully organised.”
Next, the cross members to the side girders on both sides were flame cut and removed, taking the old walkways with them, and the new walkway spans were installed with small road-rail lifting machines.
These were rail modified Case 988s supplied by hire firm Hydrex and in tandem lift they could handle the up to 9t walkway sections, manoeuvring them onto two small 5m long flatbed trucks that each road-rail vehicle pulled along with it.
Further substantial cutting followed on behind once the gantry was positioned and the hoists were in place to hold the freed deck sections. The gantry ran on skid shoes on the box rail section and was moved into place with power Tirfors.
Both conventional flame cutters and extreme high temperature thermic lances were used to slice up one of the old track spans, working from support on the other track. The old was removed in two layers – the deck and the main support girder assembly.
“That left the span empty, which gave us room for work on the piers tops and installation of bearings,” said Wyld. Part of the contract was to repair any damage to the brickwork clad iron piers beneath and particularly to pier tops. A number of precast concrete replacement tops sat in the main depot ready for use.
“A key reason for using two gantries was to allow this space for pier work,” said Wyld. “Doing two spans a day meant we could run three days behind with installation of the new sections. The gantries were too busy to run back and forth for both jobs.”
The new bridge used single steel troughs spanning between the piers. Within this, rails were mounted directly using the relatively new Vipa Baseplate system of rail chairs bolted directly to steel stools on the deck.
The old decks and the new were taken out to and brought in from road deliveries to two depots up the line where Scottish crane hire company Weldex supplied a 150t capacity crawler crane and a smaller 50t unit for the “demolished” material handling.
On a tight schedule of six day working, high winds meant re-programming, to do three rather than two spans daily. Wyld concluded: “When it came to site hazards, there was flash and burn danger from the thermic lances, movement and heavy materials and equipment all around.”
The job was completed on schedule.
