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Ashford's heart

Cutting through: A tunnelling rethink on the Ashford section of the Channel Tunnel Rail Link has helped boost progress. Antony Oliver reports.

A former agricultural auction house on the outskirts of downtown Ashford is now the hub of activities on the Channel Tunnel Rail Link's biggest contract.

Kvaerner Construction has been on site since last October and has been busy installing hundreds of 900mm to 1,500mm diameter piles - each up to 42m deep and reinforced with 40mm or 50mm diameter steel bars - to form the retaining walls for 1.8km of cut and cover and retained cut tunnel.

East of Ashford, Kvaerner's job links with Balfour Beatty's £75M contract to take the CTRL to the Channel Tunnel entrance. To the west, it will join up with Hochtief's £85M contract across mid Kent to the North Downs tunnel (NCE 22/29 July).

Piling began in February and so far Kvaerner has installed around 1,400 of the 2,665 piles.

Achieving this work rate has much to do with the excellent weather since work began but also bears testimony to the organisation and the way the contract is being run. Value engineering by the whole construction team early on has simplified work and rationalised the programme to mutual benefit.

'The project is now totally integrated - everyone on site works for the Channel Tunnel Rail Link, rather than for the contractor or the engineer,' says Kvaerner deputy project director Robin Williams. 'I don't think any of us was used to it. We all had to get through the first few days of discomfort before things settled down.'

The benefits, he insists, are clear. While the partnership does not automatically guarantee that things do not still go wrong, he is convinced that problems are identified earlier and so dealt with more quickly. 'There are fewer surprises,' he says. 'We know that we are going to have a problem and sweep up areas of work earlier.'

Rail Link Engineering contract manager Alasdair Cathcarte agrees. Working in partnership is fine, he says, but the contractor still has to get on and do the job. 'Just because we all work together does not mean it does not matter when things go wrong. The contractor still has to perform and we are still there to make sure that it does.'

And there is plenty of opportunity for things to go wrong. Contract 430 at Ashford is certainly one of the most complex on the Channel Tunnel Rail Link. At £150M, it is by far the most expensive, costing almost twice as much as any other package.

Technically, there are many challenges. Ten kilometres of the 15km contract involve constructing an at grade, two way high speed railway, and a 1.25km viaduct. But the really complex stuff is the tunnelled section through urban Ashford.

The internal walls of the four track 570m western end of the tunnel are formed by insitu concrete, reinforced with universal columns. This section joins on to a 422m twin track cut and cover tunnel. It also carries a flyover to allow trains stopping at Ashford International Station to cross the main line. Around 800m of propped and retained cutting then brings the CTRL main line back to the surface east of the town centre.

Driving the new line through the middle of a residential area is difficult enough. But add to the this the complication of having to tiptoe around live railway lines carrying commuter and Eurostar trains, and the site suddenly becomes very compact.

During the six months before work began on site, the joint team interrogated the design and made several significant changes. For a start, bottom up construction will replace top down where possible on the two sections of the cut and cover tunnel.

Top down construction would have made excavation work more difficult as it would have had to take place in a relatively cramped space under the roof slab. The bottom up method also allows greater freedom for moving equipment and materials around by crane, although extra temporary propping will be needed for the retaining walls.

However, for the 300m of propped cutting the reverse was agreed. By modifying the permanent works and introducing additional dewatering it has been possible to construct the permanent reinforced concrete props in situ, ahead of excavation.

Increasing prop spacings allows material to be excavated between them. This removes the need for a set of temporary props to support the retaining walls while the base slab is cast.

'Tunnel construction is still certainly on the critical path but the piling subcontractor has now got an achievable programme,' says Williams. 'They have come off the worry list . We are able to give them a big volume of piling and plenty of room to work in.'

Advance planning for work on the railways is vital as Railtrack needs up to 99 weeks notice to reorganise its train timetabling. In fact, many of the hundreds of possessions on the job were ordered well ahead of contracts being signed.

'We have the railway's white periods in which to work - the dead times at night - but there are not that many as the bulk of freight goes through the Channel Tunnel at night,' explains Williams. 'Usually, it means we can work between 1.30am and 5.30am which does not give us much time.'

The next big railway possession is a 33 hour main line closure over Christmas, when a 27m long precast subway will be jacked into position. This will be carried out in conjunction with a parallel

closure to allow subcontractor Westinghouse to upgrade signalling in the area.

The Option C target cost New Engineering Contract in use on the project is geared towards sharing cost overruns and savings between RLE and Kvaerner. This means that everyone is focused on producing work to programme.

'The contract is pioneering self certification,' explains Cathcarte. 'How do you stop people cheating? It's simply about getting the people doing the work to have pride in their job and to take responsibility. No amount of checkers will improve quality - you have to start at the workface.'

Certainly no one tries to make out that this job is perfect. Things still go wrong, whether it be problems with honeycomb concrete or misplaced reinforcement. But those on the project believe that they have established a strong learning culture, so that lessons can be learned and improvements made.

'Our target is to finish on time and to budget,' says Williams. 'But there are certainly significant incentives and opportunities to do even better. And we have an enormous opportunity to do things differently here.'

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