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Remodelling Ashford

Contract 430

Contract 430

Ashford Kvaerner Construction 14.4km Target cost £150M Key features: A huge trenched tunnel through Ashford town centre. Complex interfaces with live railways including Eurostar's current line, the M20 motorway, utilities and the signalling system for much of the south east sector of the rail network. The highly complex contract has the potential to scupper the programme for the whole Channel Tunnel Rail Link if it runs off track. Country section west of Ashford appears to be well in hand. Kvaerner's management is backed up by one of RLE's most aggressively supportive teams - led by 31 year old Alasdair Cathcart.

Bringing the CTRL through the heart of Ashford is a highly complex operation made all the more difficult because Ashford had lots of railways to start with.

The high speed through lines will cross the town centre sunk within a 2km length of pile-retained cut with two short tunnels, continuing on 1.5km of viaduct to the east. The grade separated structures allow the new railway to be kept clear of the existing lines - but only after these have first been moved out of the way.

Flying junctions with the cutting and viaduct are being arranged so that Eurostar trains can be switched on to two separate tracks leading into Ashford International Station.

What this amounts to is a metre by metre interaction from one end of Ashford to the other between the CTRL construction, the railways, their utilities, highways and general services such as gas, electricity, telecom, water and sewerage.

In the centre of Ashford much of the deep trench is now in place, excavated between piles ranging between 900mm and 1,500mm diameter bored 20m to 42m into the ground. Utility diversions peak in this area at the half dozen road crossings over the top of the massive box.

Inside the sections, work is concentrated on creating the shear connection between base slab and the piled walls.

General ground dewatering allowed the formation of the shear key to be a retrofit operation, enabling Kvaerner to get the central section of the thick base slab in place early. But doweling into the piles using robotic drills and avoiding the cast-in reinforcement cages is proving to be more of a challenge than expected.

Godinton Road is a focus of activity just west of the centre (see box). A much less glamorous but similarly demanding job is under way on Beaver Bridge at one end of the station. Built five years ago, it was designed when Eurostars with high voltage overhead catenaries were planned to bypass to the north of the town. The bridge now has to be raised 500mm.

Achieving this involves a series of interlinked sequential operations to raise first one carriageway of one of Ashford's busiest roads, and then the other.

Large sidespan boxes have also to be built for pedestrian subways and the CTRL through line; masses of services diverted and rediverted; railway utilities, and especially signals, avoided; and high security maintained all the time because the site abuts the present international platform.

At the other end of the station it is the railway utilities crossing under the old carriage sidings that are causing headaches. CTRL will ramp up on to viaduct near this point and clear spaces are needed every 16m for the piled foundations. New carriage sidings have just been completed nearby by Kvaerner and rail subcontractor First Engineering which has freed up the space for CTRL, but now the old tracks are being pulled up the cabling is turning out to be even more complex than expected. Adjacent to the site is the main south eastern regional railway control centre. Exploration to confirm the positions of known cable runs and discover any that are not recorded involves meticulous hand excavation.

Once all cables are found and identified, diversions have to be agreed so they can be re-routed during prearranged switchouts. As RLE project manager Alasdair Cathcart puts it: 'I'm not earning. But spending.'

Options being considered include changing to mini piles so that rigs can be lifted into place instead of tracking over the cable ducts.

Further east, Kvaerner Cementation Foundations is currently busy piling the other end of the viaduct near to the site of the project's Christmas holiday job, a subway pipejack.

The antique level crossing at Aylesford Place is set to be stopped up when CTRL's tracks run through beside the existing line. The pedestrian subway to replace it is a 1,000t monolith box which had to be pushed under the existing line, skimming not much more than 1m below track level. It was an operation that could only be done during a full John Hollaway Kvaerner project manager C430 Kvaerner's man in charge of the contracting workforce comes across as the quieter and calmer of the double act running the highly complex project in Ashford.

Hollaway joined Kvaerner 18 years ago, when his part of the company was known as Cementation. He worked in the south west area office. Two years at Faslane followed. 'Everyone always talks about the piles! The ship lift there works well, ' says Hollaway.

Then he was back to the south west, to Bristol and as contracts manager for Trafalgar House companies Willett and Cementation. In Mexico for two years, Hollaway looked after Trafalgar House's interests on the civils side.

Heavy engineering back in the UK - on piled slot that brings the A12 extension into London from the M11 - was a good precursor to Ashford. 'I came here in September 1998.'

Alasdair Cathcart RLE contract manager C430 'We're the critical path of all of CTRL and there's no denying we've made a fantastic start, ' declares Alasdair Cathcart.

Cathcart joined Bechtel after finishing his civils degree at Heriot Watt University 11 years ago and pitched into a series of major projects worldwide. The Channel Tunnel was followed by BP's Grangemouth oil refinery, Bahrain aluminium smelter, a motorway in Turkey, a Saudi Arabian polyester plant and a desalination works. He joined CTRL in August 1996.

Blending his team with John Hollaway's of Kvaerner, Cathcart takes a bullish attitude to driving the project forward and overcoming obstacles which might frustrate progress. 'Because it's cost reimbursible I'm as interested in productivity as the contractor.

'We're now 77 weeks into the contract (speaking on 21 February). We've got to hand over the country section on week 161 and Ashford on week 169. It in burned in to the back of my head.'

possession of what is presently Eurostar's only possible route from the Channel Tunnel. That meant using a Railtrack Christmas maintenance closure or facing a punitive charge. In the event the contractor assembled its own specialist team and the box was successfully jacked in place within the 33 hours available before Boxing Day afternoon.

At the other end of the town, excavation through the former barracks area had to be carried out very carefully with specialist ordnance disposal firm Bactec International on hand to deal with any explosives found.

Now there is a spoil mountain of stockpiled clay awaiting a through route to C430's 10km country section where it will be used in mitigation works. In all some 0.6M. m 3will come out from the huge town cut.

The country section appears straightforward after the complex interactions within Ashford, but it is a major piece of construction with big structures. Two of the dozen bridges cross and recross the A20, one of which was cast last month in a single, massively reinforced, 580m 3pour.

There is a short tunnel near Westwell Leacon. At Pluckley Road the CTRL will create a new landmark beside the M20 motorway with a deep cut bridge that has a separate strut below deck level.

Crossing the M20 on a skew involves a major steel composite bridge subcontracted to Jackson. The two deck sections were prefabricated in a special bay tucked in beside the motorway while the concrete piers were put in place with just a single lane closure on each carriageway.

Total closure of the M20, roll out and placing of the bridge by Econofreight was set for 18/19 March. A closure the following weekend will allow the parapets to be craned into place and fixed.

So far C430 has had 100% success on these carefully planned events. 'We haven't missed a single date on the critical path, ' says Cathcart. 'It's going to be a testing time between now and September.'

Power steering

Splicing the CTRL into the existing railway system at Ashford and Dollands Moor is a major £60M project for contractor Mowlem and its consultants Symonds Group, for track, Westinghouse for signalling and WS Atkins on the electrification system's overhead and third rail.

There is also a very close interface with the civils contractors on C430 and C440 together with Westinghouse Signals which has a £6M contract to reconfigure the signalling interlockings at Ashford.

At present the entire rail complex in the area has the standard Southern third rail DC power system.

Essentially the modification package involves overlaying a 25kV AC overhead power system through the existing lines in central Ashford and carrying out a highly complex sequence of track slews and replacements to the permanent way.

Existing tracks have to be shifted out of the way of construction works for the CTRL through lines on their grade separated alignment, sometimes more than once, and then reconstructed after the CTRL work is complete. The work has to be done within a live working railway which also happens to carry all intercontinental traffic.

Designs for all infrastructure have to be agreed with Railtrack and timing of its installation fitted around possessions of the track negotiated many months in advance. Penalties for interruption of traffic or the cost of a specially arranged closure of the international lines are huge - up to £1.4M for a weekend.

Track remodelling will occur to provide for connections from the CTRL to the existing railway and to provide facilities to enable train operators to meet their current service levels. Electrical subtleties include the need for isolating transformers to prevent the high voltage overhead AC wires inducing unwanted currents in the DC rail system.

At Dollands Moor the connection into the freight yard has to be completed within a high security environment that is as strict as the airside of an airport.

Another connection to the existing rail network has to be made at Beechbrook Farm west of Ashford where materials will be fed into CTRL for its system-wide track construction.

Box room

Frantic construction activity in the the centre of Ashford presently reaches a peak where Godinton Road once crossed the Maidstone railway. It is the spot where CTRL through tracks will dive below the old railway, some 18m below ground level.

Making the box in which the high speed line will run involves a tight sequence of operations, all of which have to be geared to long-planned possessions of the railway.

First of the key dates was 8/9 January this year when the old brick arch carrying Godinton Road had to be demolished in a single 24 hour operation. Missing the possession would have delayed all subsequent work, putting CTRL's programme in jeopardy.

Now there is a tremendous concentration of earthmoving, piling and silent sheet piling machinery working away from 7am to midnight installing the first section of CTRL tunnel box tight up against the east side of the Maidstone line. It has to be ready and waterproofed by 22 April for handing over to Mowlem which will slew the tracks on top.

Construction work will then start up on the west side to finish the box within the railway zone ready for the tracks to be slewed into their final alignment in November.

The whole site is being continuously dewatered by pumping from dozens of wells to stabilise the soft silty clay. A massive gravity retaining wall is going in along the north side to support the soil behind the remaining houses in the terrace which CTRL cut through.

Just to complicate the stack of intersecting lines and roads it is also the point where the two CTRL tracks switching to and from Ashford Station will curve around outside the Maidstone line and ramp down to meet the high speed line.

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