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The twilight zone

London Tube maintenance - What happens between midnight and 5am on the London Underground- Ruby Kitching joined the night shift to find out.

If there is one thing that really annoys London Underground passengers, it is the curt, automated tannoy announcement that 'Service is suspended on the [pause as the message is spliced together] 'X line' [pause] 'due to' [pause] 'overrunning engineering work'. Sighs and dark muttering are heard throughout the carriage and the temperature rises.

This is a common experience for commuters on the Tube, especially on the Northern Line. The 58km long, deep level, north-south route is the busiest and one of the worst performing services on the Underground.

The Northern Line is public private partnership (PPP) contractor Tube Lines' biggest headache.

In the small hours of last Friday morning, NCE joined Tube Lines staff on the southbound Northern Line track at Elephant & Castle station in south London to find out what it is doing to relieve some of its problems.

Midnight:

Maintenance and renewal gangs gather in nearby streets ready to start work at 00.30am on the dot.

00.30:

Later than expected, the final train of the night train leaves the station and the last revellers spew out of the station past 50 staff armed with mops, buckets, and dressed in full personal protection equipment, poised to swarm down into the tunnel.

01.00:

The protection master confirms that current on the rails has been switched off, allowing the night shift to descend to the station platforms. Access to the platforms is via lifts and it takes six loads to get the work force assembled for a safety briefing.

01.10:

Thirty chattering workers pull compressors from behind station hoardings and connect air and water pipes. Water sprays are switched on to cool sections of tunnel. The mist they create evokes the set of a 1980s rock video - except that it is not Jennifer Rush disappearing into it, but six burly men carrying jack hammers.

01.15:

More equipment is carried by trolley to the work site - 50m south of the southbound platform at the Elephant & Castle. Tonight, engineers are preparing to realign 400m of track, which is at a steep gradient and on a curved alignment. 'There's a twist so we're replacing it, ' says straighttalking Stuart Elgar, project engineer for subcontractor Grant Rail-Trackwork joint venture.

The curve and gradient mean the track is subject to higher wheel loads (see News). A speed restriction of 20mph - half the normal line speed - operates over the stretch being replaced.

Realignment means breaking out the concrete beneath the baseplate fixings and resetting the rail. Sections of older concrete are harder than newer concrete and cannot be broken out using hand held hammers.

'Every night is a challenge, ' sighs Tube Lines senior project manager Matt Lagar. 'Having just three and a half hours a night to work means that we have to make sure we're using the right methodology for the job. We'd love to use bigger machines but by the time we get them down to site, it's time to take them back up again'.

Instead, hand held drills are used to bore contiguous holes in the concrete, known as 'stitch drilling' so that clumps of it can be broken out later. It is a laborious way of doing the job, extending the relatively simple task of replacing concrete sleepers and tunnel base sections over many nights' work.

The largest piece of machinery, which reaches the tunnel every night by lift, is an industrial vacuum cleaner. But the Elephant & Castle crews consider themselves lucky, as at other stations with only escalator access the size of plant which can be carried is reduced to that of a pushchair.

Lagar is keen for long-term line closures so that his team can carry out more work. 'If we renew large sections at a time, it'll give the maintenance gangs less to do and improve overall service reliability more quickly, ' he says.

01.30:

All conversation ceases as dust masks and safety goggles are donned and three gangs of at least six men begin the drilling and breaking out work. 'Tonight we're hoping to break out [the concrete in] three to five sleepers and around 10 baseplates, and do as much stitch drilling as we can, ' says Elgar.

02.00:

The temperature has risen to about 40°C. Sweat drips and the air is thick with concrete dust. It is dark except for the fluorescent lights which illuminate each gang of workers. The air is cooler where water is sprayed, but stiflingly humid. Deeper in the tunnel where the water doesn't reach, it is excruciatingly hot and dry. It is also deafeningly noisy.

and workers have to be careful where they drill as they can be less than 2m apart.

03.00:

In the dust and din, unable to communicate with one another, men are working like machines.

As well as track workers and cleaners, occupational health officers monitor the temperature and airborne particles in the stations.

There are also managers auditing the work carried out.

Tony Bleau is the handback supervisor for subcontractor Westview.

'I make sure the guys aren't just sitting on their backsides so that we can hand back the station on time.' Bleau launches into a tale punctuated by 'Tube slang' to describe what happens if gangs encounter problems, and what is involved in handing back the track in the morning: 'You tell the DOM [duty operations manager] that things are running late and the TAC [track access controller] what the new call-back time will be. We've got a Class 1 ETR [enhanced track renewal work with tighter than usual track geometry tolerances, requiring onerous checking] so I've got this massive check list to sign off.'

04.00:

Drilling stops and the clear up begins. Compressed air and water pipes are disconnected, temporary lights are dismounted and rubble is shovelled into sacks. Bleau checks that all debris and dust is cleared from the tunnel base. If left, the first train would whoosh it onto passengers.

04.15:

Dust-blackened faces emerge from the tunnels, chatting and cracking jokes - dust masks and goggles are now off.

04.30:

Equipment is packed away into storage boxes beneath the track and site safety notices are pulled down as the platform is returned to passenger use.

04.45:

Contractor Metronet is responsible for the station at Elephant & Castle and Tube Lines has to hand it over with half an hour for Metronet to wash down the platforms. Despite Bleau's pleas, the station is handed back 15 minutes later than planned.

05.00:

Telecommunication checks begin and night staff leave the station.

'It's been a good night' says Bleau.

The second of three weekend possessions to make headway with the track replacement on the Northern line takes place at the end of October. Without these, the 400m length of track reconditioning would take 12-18 months longer. Instead, the speed restriction should be lifted off the track by early November. But, laments Northern Line infrastructure manager Lee Jones, 'when the job's done, no one will probably notice the difference.'

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