“Then, and only then do we cut the wire….” Words of caution – deliberately spoken. The wire in question is the overhead line wire, the cutting of which completely stops the running of electric trains and indeed most trains. It’s not like a piece of rail. You can’t change your mind, bar in a closure rail and put on a couple of clamps to get the traffic moving again. No, you have to be really sure before you “cut the wire”.

This is, of course, common to any overhead line operation. It’s a decision that’s been made ever since the system was invented. But when you’re dealing with the upgrade of the overhead line system from Liverpool Street out to Chelmsford with traffic coming in (and out) from all over Essex, Suffolk and Norfolk, cutting the wire can prompt just that little bit of extra nervousness.

Historical background

So, why the upgrade? The suburban network out of Liverpool Street has always seen an intense service and so was an early candidate for electrification.

The LNER started to electrify the Shenfield to Liverpool Street line during the 1930s but the war delayed completion until 1949. The route was extended to Chelmsford in 1956.

Originally the system used the then-standard 1500V DC. In the mid 1950s, the British Railways Modernisation Plan pressed for 25kv AC, but there were areas with low structural clearances where 6.25kv was used – and the route out to Shenfield was one of them. By the mid 1970s it was found that 25kv could be suitable even in locations with low clearances and so the whole route was converted to 25kv by 1980.

But underlying all of the present electrification setup in this densely used part of the railway network is kit that goes back 70 years.

Network Rail is now replacing everything with a modern equivalent – an auto tension system – right the way from Liverpool Street all the way through to Chelmsford in a project that originally kicked off back in 2007.

Understandably, living with a heritage system has had its issues. A lot of the components are very hard to come by. Some have to be manufactured specially and the system is complex and heavy to work with. It has many problematic and complex failure modes so that, because of the way that the wires interlink with each other, if there’s a de-wirement on one road there’s a strong potential of other roads being taken down as well. The system that is being put in simplifies everything significantly.

Logistic problems

Clive Woods, Network Rail’s project manager for the upgrade, explains: “What we’re doing at the moment is replacing about 40% of the structures to take the new equipment. It’s quite a substantially different design.

“We’re using what we can where it is suitable – where it’s not taking particularly high forces. But on the areas where forces are high we’re using the new Autotension equipment – which is fundamentally a balance weight system.”

The system is known as the “Great Eastern Furrer and Frey”, named after Electrification specialist Furrer and Frey which is predominantly the designer and also the manufacture of most of the equipment.

There are huge logistic problems. Everything is done on a piecemeal basis. “It’s not like a green field site where you can go in, put your structures in, wire it…. it’s very much more complex.”

All the new equipment has to be installed in and around the existing which has to remain in operation until switchover.
“It’s one of the big problems we have in delivering this work because we’re here in this very busy route and we have to put the service back into operation when the first trains start running – usually at 04.00 on a Monday morning.”

New foundations

The new equipment is lighter – it’s physically smaller than the existing – and as a result in some areas there can be improvements where signal sighting has been an issue.

None of the old foundations are being used. There are new foundations for each new structure. Some are concrete slabs – side bearing foundations. Most supports are tubular piles which are either vibrated in or driven. It all depends on the area and on the soil conditions. The vast majority go in without any issues at all but, inevitably, in some of the areas involved – especially those in cuttings where the space is extremely limited and in areas with complex soil conditions – there are occasional problems with pile refusals.

Screw piles have been used and mostly they’ve been very successful, but occasionally they’ve led to problems because they have a higher tendency to refuse. If there are obstructions in the soil which maybe the ground investigation survey hasn’t picked up – even tree roots – the piling operation can stall.

Being an area with a very long history of railway development it’s always wise to take out trial holes where it is anticipated that ‘someone has been there before’.

New kit

All the contact wire will be brand new. The old wire, catenaries and structures all go off to scrap. Bases are broken out as well, down to about a metre below ground level except where a structure base is acting usefully as part of another structure!

The scheme doesn’t involve replacing any feeds from the national grid to the transformers themselves, but all the feeds are being replaced where they go from transformers to the overhead line. In addition, all switching arrangements are being upgraded.

Signalling is not affected although signal sighting is part of the interdisciplinary checks undertaken in the design process.

But how about hidden major structures? “We’re free now, but prior to getting out to the London side of Stratford station we did have to be aware of the London Underground system beneath- especially with piling! We were communicating with them just about all the time in this area. And it was the same with the Dockland Light Railway. We were adjacent to their infrastructure for much of the way going out to Stratford.”

State of play?

By last Christmas, Marylands and Forest Gate had been completed, as had the section from Shenfield to about three miles country-side of Chelmsford. The last bit of major work prior to the Olympics was the wiring of Ingatestone station.

The tracks between Ingatestone through to Chelmsford and in Chelmsford itself will be done after the Olympic embargo through to the end of the calendar year.

Historically there has been one principal major contractor – Carillion. Their work has come to an end. What Network Rail has been doing is engaging with the market about different alliancing models that would be mutually acceptable. They are going back out to the market, probably at the beginning of the Olympic embargo, to start bringing on partners for future works.

The go-live point

Clive, who has a background in the Nuclear Industry where he was involved in the decommissioning of the Magnox reactors, acknowledges that this project has been a huge logistical challenge. “There is a very robust planning system that starts way, way back in the project. As the go-live point gets closer there are a series of go/no-go points so that unless we are absolutely sure we have all the resources available then, and only then, do we cut the wire.”