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New circuits and old bombs

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Rail projects seem to have a habit of changing over time. A seemingly simple project can alter almost beyond recognition before it is completed, often adding both time and cost in the process.

This is often caused by the problem of dealing with aging Victorian infrastructure which yields unpleasant secrets as work progresses.

However, at Gatwick Airport recently, the cause was quite different. UK Power Networks Systems (UKPNS) had a contract to upgrade the circuit breakers in the electricity substation.

This formed part of the preparations for the new 12-car Thameslink trains that were due to commence running in December 2011. An uncomplicated job, and quite routine.

Then, Network Rail decided to add a new platform at Gatwick Airport to ease congestion and improve passenger flow. Again, no real problem, except the new track alignment would go slap-bang through the electricity substation.

New substation

There was nothing for it but to build a new one. UKPNS, as the contractor on site, were asked to design and build a complete new substation to replace the existing one which would then be demolished to make room for the revised track layout.

Again, this was, on the face of it, an unremarkable project. None of the old equipment would be reused as it was obsolete. So a completely new installation was planned a few hundred yards away. It could be built and fitted out without interrupting railway operations, and when complete the supply would be switched over. “Simples” – to quote a well-known television character.

Work commenced in April 2011. As the location for the new substation compound was a prime site, it was decided at the outset to strip the entire compound area, grade, install a geotechnical membrane to prevent vegetation growth, and then add a hardcore layer to establish a good working level.

Unexpected delay

However (that’s the second “However” in this project), in August 2011, when hand digging some trial holes at the northern extremity of the site, the team came across what looked like an unexploded hand grenade. Shortly after that, a land mine and a further grenade were discovered, all approximately 1 metre below the surface.

Naturally, work stopped on site and the bomb disposal squad was called in. The Gatwick Airport Authority was contacted and a 15 minute suspension of plane operations was planned to enable the items found to be detonated in a controlled manner.

Further research revealed that some of the work area was used as a munitions dump after World War Two and that a lot of items had been disposed of as part of the decommissioning process. Apparently, it is not unusual when undertaking such controlled detonations that some of the munitions can be driven below the surface without exploding.

A decision was made to engage an ordnance expert on site full time. Zetica Limited was appointed, trial slots were dug by hand in all areas of the civil works, and ground-penetrating radar scans made at various levels to ensure it was safe to continue.

In total a further six items were discovered and were disposed of but no further controlled explosions were necessary and the ordnance expert took control of the removal and disposal of the various objects as they were found.

As the ground was littered with buried metal of all sorts, both detritus from the old railway sidings as well the remains of the ordnance depot, it was impractical to clear the site entirely. Instead, care was taken and the munitions expert monitored the whole process continuously.

All this delayed construction by a week, but there was still plenty of work for the team to do on site so the overall effect was negligible. UKPNS Project Manager David Blakeley commented that civils partner BP Howard “did a really good job” in getting the programme back on schedule.

Low lift

When those civils works were complete, the new equipment could be delivered. This was delivered to site by lorry, and arrangements were made to have it lifted off by crane.

However (that’s “However” number three!), the site is directly under the Gatwick Airport flight path. The height of the crane jibs was restricted, and even then permission had to be obtained from the Gatwick Airport Authority for the lifts to take place.

Once the AC and DC modules, both 4MW transformers and the allied smaller transformers and busbars were installed, then connection to the railway could begin. The substation has a 33kV AC supply, and the cables for this also had to be moved away from the new railway alignment.

The 750DC output is split into nine separate circuits, each with two positive output cables and two negative returns.

These 36 aluminium feeder cables, each 58mm in diameter, totalled ten kilometres of new cable installation. They were run out during night-time possessions and left near the tracks.

Connection was made over two weekend possessions in November, with five circuits being connected on the first weekend and the remaining four on the second. As each circuit was connected up, the corresponding feed from the old substation was removed and everything tested for performance and safety.

UKPNS staff worked closely with cable installation contractors SRS to make sure everything went smoothly.


Once everything was up and running, the old substation was decommissioned, the equipment taken away for scrap, and the site levelled. It was then handed over to Network Rail for them to build the new platform and track. Zetica’s ordinance expert went with it – he is still working on the site.

So, despite the delay caused by the bomb scare and the complication of the three “Howevers”, the whole installation was handed over on time.

Network Rail’s project manager Jim Buchanan was satisfied with the way it had all gone and commented that the project was a “showroom that all contractors should aspire to achieve in terms of quality, layout and future maintainability”.

Barry Dilks, UKPNS projects director, was equally complimentary:

“This project perfectly demonstrates our ability to work in a collaborative manner, not only with our client but numerous interface parties. Network Rail’s project management worked well with our people under Howard Blakely (site manager) and Carl Smith (electrical site supervisor) as a combined team to deliver a high quality result, within an agreed budget and to the timescales laid down at the outset. This ‘Can Do Will Do’ attitude shows what collaborative working can achieve and they make me very proud.”

The only loser was Network Rail’s project accountant, who had to foot the bill for the unexploded ordinance investigation. Maybe he can claim off the Ministry of Defence?


  1. Watch the spelling!

    “Ordinance” pertains to an edict whereas “ordnance” is the word for munitions. Somehow “ordinance” doesn’t quite go with the co-operative, pragmatic spirit you report between the various agencies involved or what was found underground!


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