Gearing up for Severn Tunnel electrification
Source: RTM Aug/Sep 16
Brian Paynter, head of programme, planning and integration IP Track, Plain Line at Network Rail, and Daniel De Luca, project manager at the infrastructure owner, discuss the challenges in the enabling work ahead of a significant closure of the Severn Tunnel.
From 12 September, the 130-year-old Severn Tunnel will close for six weeks to prepare it for electrification.
In the run-up to this work, Network Rail’s Orange Army has already been putting in a significant amount of work to prepare for the closure, with over 40 tonnes of soot removed from the tunnel ahead of the upgrade work.
And as RTM went to press, the infrastructure owner’s track renewals team was gearing up to carry out a significant piece of enabling work at the tunnel’s Welsh Portal over the August bank holiday.
De-risking the September blockade
Daniel De Luca, project manager at Network Rail, said the 75-hour blockade of the area is to carry out approximately 40% (600m) of the track renewal within the Severn Tunnel.
“We decided to take this out of the main work to de-risk the blockade,” said De Luca. “And because there is so much other work going on, it enables us to deliver everything the company needs within the six weeks.”
As well as replacing and lowering this section of track within the three-day window, Network Rail is also carrying out essential work to install and test part of a new signalling system for the Bristol area.
Replacing track within the Severn Tunnel is a regular occurrence for Network Rail, especially with the unique and damp environment within the structure. Brian Paynter, head of programme, planning and integration IP Track, Plain Line at Network Rail, noted that since 1998 a lot of the track in the tunnel has been renewed twice already.
He added that the enabling work, which De Luca is leading, will also eradicate the need to do some speed restriction work in the area.
Structural and logistical challenges
Although Paynter was confident about the renewal works, he said: “What makes this job slightly more difficult, in Severn Tunnel, is that there is a very large carrier drain through the middle between the two tracks – which is actually part of the structure of the tunnel.
“When they built the Severn Tunnel, back in the 1800s, they actually hit a spring. So what you have now in this drain is a large volume of water which runs through it permanently. It just hampers the renewals slightly because it is in the area when we are doing the excavation.”
Additionally, as work is being carried out at the English end of the tunnel, it means the team will have to resource all the job at the Welsh Portal from Wales, and go back out the same way.
“Where the challenge comes to us in this particular blockade is that we can usually bring our engineering trains in from one end of the tunnel to service the work and take them out of the other end,” said De Luca. “But because there is so much other work going on in this particular blockade, we can’t do that. We have to stack our engineering trains up and then bring them back out the same way.”
From a logistical point of view, added De Luca, it becomes a very difficult renewal to undertake: “In this particular tunnel, we’ve never worked in this way. We’ve done it in other areas of the network – it isn’t an uncommon practice – but it does slow down production rates.”
Once the team has completed the bank holiday renewal, attention will then turn to the six-week blockade in September.
Anecdotally, Network Rail believes the tunnel has never been closed for this length of time for more than 50 years. According to the infrastructure owner, the volume of work being undertaken means that it would take up to five years to complete if it worked to a weekend closure programme as an alternative.
During the six-week closure engineers will work around the clock preparing not only the Severn Tunnel, but also the Patchway Tunnels, for electrification.
“The Patchway Tunnels are two single-bore tunnels – one track in each tunnel – which makes it even more logistically challenging because you haven’t got another road next to you to service the materials in and out,” said Paynter.
The team will be lowering the track in the old structure by approximately 400mm, added Paynter, but there is also a drain running underneath the track the engineers will have to negotiate.
“It just adds to the challenge,” he said. “There is 750m of track renewal being done in the down tunnel, and about 400m being done in the up tunnel. Due to the stability of the structure, and its age, there are concerns about going down this deep.
“This means, we can only do part of that work in 20m sections. So, literally, you take the track out, dig it for 20m, put the new stone in for 20m, and then you put the new track back in. Then you move on to the next 20m.
“Somewhere like Severn tunnel, where we will do 600m [over the bank holiday] and 800m [during the six-week blockade], we literally go in there and take all the track out, then dig, then re-ballast it – like we would do on any normal renewal. But with the up and down tunnels at Patchway we’ve got to do the work in very small lengths.”
Paynter added that the down tunnel will take the team nearly all of the six-week possession to complete, and the up tunnel will take 16 days.
The Severn Tunnel renewal is expected to be somewhat easier, as it is one of the last pieces of work to get started and finished in the blockade. Following the initial bank holiday track work, a team of 200 Network Rail engineers will be working day and night to install over eight miles of conductor rail.
The Furrer+Frey Rigid Overhead Conductor-rail System will be installed in the Severn Tunnel – hung from brackets in the roof – which will provide the power for trains to pass through once the line is electrified.
“Once we’re back in the Severn Tunnel, we are doing another 800m of track renewal,” said Paynter.
“When we do the bank holiday work there is no OLE equipment above us, but when we get back in at the end of the six-week blockade and do the 800m section the OLE will be up.”
De Luca added that as OLE will be above the team at the end of the blockade, the working methodologies have been altered to factor this in, but both he and Paynter are confident the programme of work will be delivered on time and will provide a vital step forward in the electrification programme.
Tell us what you think – have your say below or email firstname.lastname@example.org