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Country pursuit

Contract 420

Contract 420

Mid Kent, Boxley to Lenham Heath Hochtief/Norwest Holst JV 20km Target Cost £85M Key features: Includes transit of Boxley Valley which was always one of the most environmentally sensitive sections of CTRL. Currently the exposed Weald Clay looks like Paschendale in 1917.

Mitigation landscaping should soon conceal all. Fastidious attention to keeping mud off the roads is especially noticeable on this contract, as is being both woodland and neighbour-friendly.

Most of the trace hugs the M20.

Proximity to the motorway and the A20 creates a very tight pinch point at Harrietsham. Some 2.1M. m 3of the 4.6M. m 3muckshift has already been done since the start on site in June last year. Critical to progress is completion of the rail crossing in the middle of the contract. This will enable excellent sand from the east end cuts in the Sandgate Beds to be hauled 12km or more to build structural embankments at the west end.

On the map it is the proximity of most of Contract 420 to the M20 motorway that appears to be the prime constraint on construction.

On site it becomes obvious that the motorway is incidental, apart from the pinchpoints with the A20 at Harrietsham and at the motorway service area. The key to completing civils work of this country section of CTRL on time in October 2001 is the construction in the next few weeks of four critical structures.

Only with these in place can sand from the east end of the contract to be hauled along the trace to build earthworks at the west end this summer.

Gault Clay which outcrops through the western half of the contract is unsuitable for any earthworks constructions apart from landscaping bunds. And hauling spoil along the A20 or M20 which parallel the CTRL trace is not permitted.

The structures on the critical progress path are the A249 crossing, the bridge over the Maidstone to Ashford railway, piling for the cut and cover tunnel at Harrietsham pinchpoint and a nearby realignment and bridge taking CTRL over the A20.

At the A249 the road has been temporarily realigned and the Hochtief/Norwest Holst JV is busy constructing a bridge deck at ground level across two lines of contiguous piles installed for the CTRL. Once the deck is cast the road will be rediverted so the railway and its permanently strutted approach cuts can be burrowed out beneath. Just to the east is a deep pile retained cut through the ancient woodlands of Horish Wood (see box page XXVIII).

The long skew rail over rail bridge is progressing, with its many beams lifted in during possessions.

A recent change of plan at Harrietsham has made the programme for the pinchpoint more achievable. Originally it was proposed to pull off the piling rigs for the first part of the muckshifting season and allow the wagons to track through the part completed tunnel. But agreement has just been reached with Kent County Council to allow the haul road to be diverted round the tunnel site Phil Bailey project director Hochtief/Norwest Holst JV C420 Phil Bailey joined Hochtief on the company's first project in the UK, the A38 Marsh Mills flyover in Plymouth. It has been roads ever since.

He went on to South Wales and the M4 viaducts at Neath then moved to Kent for the Thanet Way project, building a new access route to Ramsgate round the back of Herne Bay. Many of Bailey's core team from the Thanet Way came across on to Contract 420 with him for the start up last summer .

Building the high speed railway is not so different from road construction, he says. 'There's going to be ballast on top instead of blacktop, and a tighter specification for materials. The railway is far more sensitive than a road to settlement and it has a 120 year design life.'

His team quickly seized on the opportunity to earn the 25% of savings against target cost, coming up with money saving alternative schemes for three cut and cover tunnels.

Terry Rawnsley The desk is a bit of a giveaway. Terry Rawnsley has the most orderly of any contract manager on the CTRL.

His current letters and papers are laid out for inspection equidistantly spaced on the desktop. Ask him about, say, the form of contract and the document is to hand instantly from the shelf. Ask for details such as 'how do compensation events work?' and the contract is opened at the relevant para 61 to reveal neatly written marginal notes explaining all.

An Arup man, Rawnsley emphasises that his role on CTRL is a 'lot different from an old resident engineer'. 'We stand behind and observe, ' he notes. But he emphasises that RLE takes a close interest and involvement with many things that would not have directly concerned a traditional RE. 'We have our snouts into every aspect.'

and run adjacent to the A20 within a properly protected route for a few hundred metres.

Just to the east the new bridge crossing of the permanently diverted A20, the fourth of the critical structures, is nearly finished.

Since starting on site last June, the contractor has made very good progress. The project is bristling with crane jibs and Stent's piling rigs which have 2,700 holes to bore and fill with concrete. Earthmoving subcontractor John Jones has already shifted 2.1M. m 3material.

With piling completed at all critical structures but Harrietsham Tunnel, groundworks attention is currently focused on work for Boxley Tunnel - a cut and cover structure burying the CTRL at one of the most environmentally sensitive parts of the entire route.

But the combination of Gault Clay and winter rainfall has currently given the CTRL site the appearance of a First World War battlefield.

Wheeled traffic bringing in concrete and reinforcement has to be helped through the water- filled ruts by tracked equipment. And there is a constant need to check that catchponds built to intercept site runoff are protecting the local watercourses.

Value engineering by Hochtief/ Norwest Holst JV has considerably simplified and reduced the cost of tunnel temporary works. The original scheme was to dig down between the contiguous piled walls putting in three levels of tubular props, cast the invert, then cast the roof and backfill the landscaping over the top. Now the roof will be cast first, before dewatering the fissured clay, excavate in heading and cast the invert slab. This will eliminate much of the propping.

Cost saving alternatives have been accepted by RLE for two other cut and cover tunnels, at Hollingbourne and Sandway. These landbridge type tunnels were to be reinforced concrete boxes with gravity concrete walls retaining the approach cuts. Now they are to be three pinned arches in precast concrete craned in onto pad foundations.

The approach cuts will be retained by Reinforced Earth Company cruciform panel walls.

Construction time is estimated at only two thirds of that needed for the original scheme.

If the bulk earthworks are completed as planned this year it will enable the Hochtief/ Norwest Holst JV to concentrate next year on the 40km of trackside drainage that has to go in along with batter drains.

Richard Gethin RLE community relations C420 Drive around Kent with Richard Gethin and you soon get into an I-Spy mode - looking out for clods of mud on the road, misplaced temporary diversion signs, utility subcontractors using private drives as turning places, site runoff polluting streams, and anything else that could irritate people who are having CTRL built on their doorsteps.

Gethin's job is to seek out activities that could be an annoyance and then do what ever is reasonably possible to deal with the cause. It involves a mix of policing, diplomacy and persuasion. He is the one in the front line when people call to complain about some construction activity which is upsetting their neighbourhood. Quite often these annoyances turn out to be nothing whatever to do with CTRL but they still have to be dealt with.

Qualifications for the task include a civil engineering degree, a spell in the army, then an MSc in distribution technology and management plus some time in that industry.

Since joining the CTRL seven years ago, Gethin has built up an intimate knowledge of its interaction with the local communities. He worked on setting up the information centres established when the Bill was going through Parliament.

Woodland work

'New' ancient woodland is being created on an unprecedented scale in a patch and mend operation throughout the length of Section One.

It will more than make up for the Kent woodlands torn up to make way for the CTRL.

During the project, 230ha of replacement woodland is being planted using translocated soils, seedling tree 'whips' and in places by moving complete stumps of mature trees. A strategy is being followed in which gaps are being filled in between isolated sections of woodlands near to the line of the railway so as to make up continuous blocks of a sustainable size for flora and fauna.

Translocation has been done before, on projects such as Manchester Airport's second runway, but never so extensively.

The trace of the railway crosses woods at many places between Ashford and the Waterloo turnouts on Contract 330. The typical mid-Kent lineside landscape includes a sectional cut through woodland, notably at Boxley, the east end of the Nashenden Valley, and west of the Medway where the CTRL takes a smooth curve within the kinked line of the M2 motorway.

Most of Kent's woodlands were harvested for centuries as coppices - a continually renewing resource of timber saplings with a multitude of uses in pre-industrialised England.

Cessation of that harmonious interaction with man has allowed time for stumps in many woods to mature into large multi-trunked trees.

'Ancient' is defined as 400 plus years old woodland, regardless of whether it has been cut back regularly. Coppicing simply created clearings on a rotational basis and the provenance of the woodland continued relatively undisturbed in the ancient soil, seeds and mulch between the continuously resprouting stumps.

Moving the woodland involves felling and clearing the timber followed by a painstaking operation to rake out the understorey material between the remaining stumps. This is loaded into dumptrucks, with a minimum amount of contamination, for transport to the receptor site.

Where the receptor site has a recent previous use for agriculture it is necessary to strip 200mm to 400mm of soil to remove the excess fertiliser.

Old woodland soils are relatively infertile and the farmers' nitrates would upset the balance of the translocated soil. Some of the smaller hazel stumps are being moved but the majority of the translocated woodland is being created with new planting.

As a preliminary to the operation a contract was let in 1996 to Oakover Nursery. It collected seeds from the trees that would be lost and germinated them for transplants.

Some 1.2M additional seedlings, as one or two year old whips, are being grown for the project by Crowders Nursery in Lincolnshire using plant material from England, 25% of it from Kent.

This winter has been a peak in the planting operation. RLE and Railtrack have a continuing obligation for five years to arrange for replacement of whips that do not survive.

Expensive modifications to the design of the railway have been made to reduce the severance of the ancient stand of timber at Horish Wood. There the Parliamentary Bill had envisaged wide sloped sides to the CTRL cut through the soft Weald Clay - involving a substantial destruction of what was left of the wood following construction of the M20.

Local negotiation led to the decision to slot the railway between massive, and expensive, contiguously piled walls. It meant that much of the wood could be left untouched.

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