Recent articles in Rail Engineer have highlighted progress of the £2.8 billion electrification of the Great Western main line (GWML), now planned to be completed in 2019. The last two articles focussed on the east of the city of Bath, between Bathampton Junction and Box Tunnel, and then preparatory work carried out between Bath and Bristol.

The electrification project now moves on to probably one of its biggest challenges: the electrification of the 7.012km long Severn Tunnel. The tunnel will be closed to trains between 12 September and 21 October for the work. It is referred to as the “Severn Tunnel Autumn Disruption” or STAD for short and, just to make it a bit more interesting, included in the STAD are the Patchway Tunnels –1.139km Old (Down); 0.057Km Short (Down); 1.609Km New (Up).

The STAD is a critical milestone in the project to deliver electric trains for passengers in South Wales and forms part of Network Rail’s Railway Upgrade Plan to provide a bigger, better, more reliable railway for passengers.

Economic boost

As well as improved journeys, economists expect that the electrification of the line to London will deliver a significant economic boost for South Wales, resulting from the improved connectivity. This was a critical factor for attracting investment for the electrification of the route.

But before considering the engineering challenges for a moment, let us just cast our minds back to the incredible legacy left by the Victorian railway engineers: the Severn Tunnel itself. It was built by the Great Western Railway to provide a direct link between London and South Wales, following GWR’s acquisition of the South Wales Railway in 1861. Although work started in 1873, Thomas Walker was in charge of the project from 1877 until its completion in September 1886 and the Engineer-in-Chief was Sir John Hawkshaw.

Cardiff - Severn_Tunnel_Junction

More than 76.4 million bricks were used in the construction. In October1879, the tunnel workings were flooded by an influx of water coming from an underground river, now known as the Great Spring. This necessitated the construction of a pumping station at Sudbrook on the Welsh bank which is still working today, albeit with more modern equipment. Throughout the tunnel’s life, between 10 and 20 million gallons of water have had to be extracted every day to prevent flooding.

Reading the exploits of the divers involved, especially one named Lambert, we gain an understanding of the bravery and commitment required to ensure the Tunnel was built. It also highlights the different value we now put on safety and the lives of those involved in the construction.

Fresh air

Two of the three pumping shafts contain a lift for access to the tunnel for maintenance gangs and emergency purposes. At Sudbrook, there is also a ventilation shaft through which 80,000 cubic feet of fresh air can be forced into the tunnel each minute by means of an eight- metre diameter fan at the top.

Many of these access facilities are being used during the six-week closure by Network Rail’s contractors, which will be working all day and night to install over eight miles of conductor rail, designed to provide power to the new electric trains.

As already stated, a significant amount of preparation work is being undertaken ahead of the upgrade and this was described by Daniel Tipper, Network Rail’s area director for Great Western Route Modernisation Wales. Right at the outset, Daniel emphasised the importance of the framework contracts that are in place, highlighting the enormous benefits that are emerging from the atmosphere of collaborative working that exists.

Teams come together dependent on the challenge posed, but a joint venture of Alstom, Babcock and Costain (ABC) is the principal contractor, working for Network Rail’s tunnel team. In turn, ABC uses Arup for design support alongside Furrer and Frey for conductor beam technology and Donaldsons as tunnel specialists. AMCO provides experienced specialist construction support to ABC and there is a whole host of experienced suppliers in support.

Preparatory work

A significant amount of preparatory work is currently underway dating back to July 2014. Taking advantage of possessions of up to 50 hours, the bulk of 7,000 autotransformer feeder (ATF) anchors have been installed ready to receive the autotransfer feeder cable. These 565mm steel bars are installed every two metres throughout the tunnel over both tracks. However, the contractors first had to scarify 2,500 square metres of tunnel lining to remove more than 35 tonnes of soot, examine the brickwork and then carry out brickwork repairs where necessary.

Cardiff - Severn_Tunnel_Junction

The team designed six purpose- built rigs, each one consisting of three telescopic arms with detachable drill heads. The individual rigs are rail mounted and propelled by a road/rail vehicle. Each rig is remotely controlled, ensuring individual safety.

It takes one minute to drill three holes and all dust and residue is captured in a vacuum pack. It is a relatively cheap, simple, safe and impressive solution. The team also designed scaffold frames which follow the drilling rigs, inserting the resin, bars and wedges in groups of six.

Whilst this work is underway, the tunnel lining is being checked and poor brick work is being replaced. A simple task, one might think, but one that requires a high degree of skill.

Also, understandably, water is leaking into the tunnel at spots throughout its length so old deflector sheets have to be replaced or new ones installed. Daniel pointed out that this period of preparatory work has been invaluable for the project. It has given them confidence that their ideas are working and, although the tunnel is posing many challenges, the structure is in better condition than they expected. Strong links have been developed with local suppliers, especially those associated with welfare requirements, a key element of the project as more than 200 people will be involved with the STAD.

Once the anchors are in place, the fitting of the conductor beam and supporting equipment is challenging but logical and, if organised properly, repetitive. The plan is to start at the Wales end on the Up line and work through the Severn tunnel, proceeding onto Patchway Tunnels then returning on the Down line back to Wales.

A training school has been set up in Cardiff and, using local people wherever possible, a process is being developed that will enable materials, equipment and a skilled workforce to construct the Furrer and Frey Rigid Overhead Conductor Rail System (ROCS) as if they were on an assembly line. AMCO, as specialist suppliers to ABC, is delivering and carrying out this phase of the work.

Whilst this work is underway, 1km of track will be renewed and lowered in the Down Patchway Tunnel as well as a significant amount of drainage work. Good track quality and alignment throughout both Tunnels is essential with a ROCS system. Fortunately, the Severn Tunnel alignment is quite good but the curvature in Patchway leaves a lot to be desired and is commanding a lot of attention from the design team at present.

Cardiff - Severn_Tunnel_Junction

Logistics are key

As can be imagined, this is developing into a potential logistics nightmare and is taking up a significant amount of time for Daniel’s team. Sticking to the principle that they will work up one track and down the other, detailed studies of road-rail movements and engineering trains are being conducted.

Many questions have to be asked, and answered. What to do if there is a breakdown? Do temporary ramps need to be constructed for easier plant and road-rail movements? How to ensure that the right equipment and material is reaching the right place at the right time?

It’s not a new challenge, all projects require careful logistics management, but it doesn’t take a leap of imagination to realise that the logistical problems in this case are complex, of paramount importance and deserve the time and effort that Daniel’s team is clearly putting into it.

Network Rail claims that, without the six-week closure, it would take five years to complete the electrification of the Severn Tunnel. This puts into context the work that is being undertaken during the STAD. It will give South Wales a high speed, electric rail link to London. It will also help
to complete the task of bringing the GWML into the twenty-first century.

There is a lot to do, the many different companies involved have come together to form one single team to deal with the challenges that this work presents.

You never know, even Mr Lambert might be looking on. He was the nineteenth-century diver who risked life and limb, struggling underwater in the pitch dark in the tunnel to open a sluice gate in order to alleviate the flooding and thus enable the Severn Tunnel to be completed.

Certainly, the preparatory work currently underway implies that all is being done to ensure that the work is completed successfully. Then Daniel and his team can take a well-earned holiday.

Photos courtesy of High Viz Media