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An organic bank account

Site Report; An unusual building with a very unusual end use has thrown up a variety of challenges for contractor James Longley. Now that successful completion is looming, the firm can be proud of its involvement in a structure which should be standing fo

THERE are signs of life in the clammy soil surrounding Wake-hurst Place; it is not the emerging spring flowers but humans and machines forcing their way through the dank West Sussex soil.

In the lee of the ancient house at the heart of the Wakehurst Place estate, contractor James Longley is building a project unlike any-thing the firm is ever likely to tackle again.

The Royal Botanic Gardens (RBS) came up with the idea of a bank to store endangered species of seeds but, until the arrival of the National Lottery, the proposal remained dormant.

The Millennium Commission allocated £30 million of lottery cash in 1997 and the scheme was finally kicked into gear.

'When I first heard about this project, I thought 'that's a Longley job',' says Graham Todd, a direc-tor of the firm.

The locally-based outfit beat a clutch of national firms, including Birse, Carillion, Laing and Sir Robert McAlpine, to the contract and it has provided perfect rehabilitation for Longley after one of the hardest periods in the firm's history.

Longley clinched the deal in April 1998, soon after an ignominious exit from its largest-ever contract - a £35 million deal to rebuild Chelsea FC's Stamford Bridge stadium in west London.

The firm was red-carded from Stamford Bridge after falling foul of the club's owner, Ken Bates, and soon after ownership of the firm passed out of the hands of the Longley family and into those of venture capitalists, Postern.

The seed bank fitted Longley's background in specialist projects, such as the restoration of Hamp-ton Court Palace. But it also featured enough technical hurdles to frighten off many contractors. One such hurdle was dealing with the legacy of a groundworks package carried out by another contractor six months before Longley won the deal.

Longley project manager Steve Constable explains: 'There was4 m of clay over the underlying rock. The idea of doing the dig first was to allow the clay to heave over the winter.

'The firm that did the ground-works took the original heave off and carried out a survey, so when we got here it was very loose and we couldn't really get a level off the site.'

When Longley moved on site soon after winning the contract it was immediately faced with a piling operation to underpin what was essentially a 13,000- tonne con-crete box buried into the side of a hill at Wakehurst Place.

Longley installed 30 piles with a 2 m diameter down to 9 m, under the actual seed bank itself, which acts as a giant cold store. In addition to these, a further 164 200-mm piles were sunk into the site plus 69 with a diameter of450 mm down to 7 m.

Mr Constable, who spent a year as senior site manager on the job before moving up to project manager, says: 'The piles varied in depth depending on where they were in relation to the building and the load they were taking.'

The piling took three months to complete. It was covered by a 375 mm- deep layer of crushable polystyrene in case the substructure, which has been guaranteed for an incredible 500 years, moves.

Mr Constable adds: 'We were worried about heave, so the building is not only held up but also held down.'

Longley has been work-ing with its subbies and the architect, Stanton Williams, to specify the fittings, most of which are unique because of the nature of the scheme.

Mr Todd explains: 'There are lots of glass, metalwork and pre-finished items. The problem has been that nothing was bought off the shelf and often we were starting from scratch.

The procurement period has been a considerable test for the site team and the architect's management team.'

Longley is working under a Joint Contracts Tribunal contract with a number of clauses attached to it, including Contracting Design Portion (CDP) supplements. This places more responsibility on Longley and its subcontractors and, because many parts of the scheme are one-offs, most materials were dispatched to Taywood Engineering for testing.

Mr Todd says: 'If stuff doesn't fit when it gets here, it's not thearchitect or the design team that's got the problem: it's us. This is where the CDP business comes in. We've got to make sure it all works. It's been an intensive management business.'

Longley had already cultivated a successful relationship with the Royal Botanic Gardens on jobs at Kew Gardens, but the seed bank contained one element that could have soured this.

A dozen cast concrete barrel vaults, which are 14-m long and7-m wide top off the bank itself. Any problems with these could have seriously delayed work and had severe consequences for the £13.5 million construction budget.

The vaults were not pre-cast but were poured in situ. This aspect was so critical that Longley built a dummy section by the site office and spent three months working out an action plan.

Mr Constable explained: 'There was no method to this, so we had to develop one with the concrete sub-contractors, Duffys.

'We poured the barrel vaults in one go and had two shutters running in tandem, pouring one complete vault a week over 12 weeks. This had to be right.'

The job had its hairy moments but Longley employed a strict checking regime with Duffys on the barrel-vaulted timber shutters used for the concrete pour.

Mr Todd said: 'We were work-ing to very strict tolerances at that stage. If one of these had gone wrong, it would have seriously delayed the project and cost a lot of money.'

Instead, Longley emerged unscathed and the firm is now finishing the project's relatively uncomplicated services.

The May 26 hand-over date is now on the horizon and the scheme looks like ensuring Longley's relationship with the society remains in bloom.

Colette Grosse of the RBS comments: 'There's been a few hiccups, but Longley have overcome them all and really deserve a pat on the back.'

Project details

Project: Seed bank.

Value: £13.5 million (construction cost).

Programme: April 1998 to May 2000.

Client: Royal Botanic Gardens.

Architect: Stanton Williams.

Main Contractor: James Longley.

Concrete subcontractor: Duffy.

Structural glazing & cladding: Stewart Fraser.

Mechanical & electrical: Drake & scull.

Partitions: Optima.

Stonework & paving: PAYE.

Stainless steel roof coverings: Cleveco Roofing & Cladding.