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A taste of Eden

The biomes of Nicholas Grimshaw & Partners' Eden Project have transformed a Cornish china clay pit into a breathtaking world of rainforests and moonscapes

Ifthe next James Bond film does not make use of the Eden Project there will be something very wrong. It has everything:

Amazonian rainforests; eerie moonscapes; and ominous shimmering mega-structures which bubble out of the ground. It already has something of a cult status, with media coverage and word-of-mouth eulogising proliferating to such a degree that any formal marketing spend has been kept to a minimum. But just in case the gossip has not come your way, the Eden Project, designed by Nicholas Grimshaw & Partners, is 'a showcase for global biodiversity and human dependence on plants' located in a 15ha former china clay pit near St Austell in Cornwall.

The 'experience' is divided into two linked climate-controlled 'biomes' - one which recreates the rainforest of the humid tropics and one which apes the warm temperate climate of the Mediterranean. Each of the biomes is made up of four joined domes which span up to 130m. The largest biome is 240m long, 55m high and 110m wide: enough space to accommodate the Tower of London. Everybody seems to have their favourite Eden statistic.My preferred nugget of useless information is that the scaffolding merits two entries in the Guinness Book of Records as both the largest and the tallest structure of birdcage scaffolding erected anywhere in the world.

The Eden Project is due to open next month and, unusually for a millennium project, visitor numbers look set to far exceed early expectations. Even under construction, it attracted more than 3,500 visitors a day - a figure which is only just shy of projected numbers once it is complete.

The basis of its appeal is complex. Few could fail to be seduced by the prospect of such a large, strange community of buildings hidden below ground level like Arthur Conan Doyle's Lost World. But it is far more than simply a spectacle: to the National Trust crowd it is the ultimate greenhouse; to environmentalists it is a tribute to matters ecological; and to children it is a cluster of space-age bubbles with interiors which look like a cross between an adventure playground and a film set.

To architects it is a geodesic structure significantly larger and lighter than any built before. The domes are constructed from self-supporting and interconnecting tubular steel hexagonal frames. The largest of the hexagonal planes span 11m, on a framework of steel tubes only 193mm in diameter: a filigree structure akin to a spider's web.

The cladding takes the form of hexagonal inflatable 'pillows' of translucent laminated ETFE foil, the largest of which has a surfaced area of 75m 2and is 2m deep. ETFE has a life expectancy of 25 years, and there is an expectation that a smarter material may be available by the time it needs to be replaced.

But its credentials are pretty good.

Compared with glass, ETFE is half the price, has better thermal insulation properties and transmits more ultraviolet light, a quality which is particularly beneficial to plants. It is also just 1 per cent of the weight of glass, making the entire structure lighter than the air it encloses - with the wind in the right direction, and without sufficient anchoring, the bubbles would simply fly away.

But as Andrew Whalley, director in charge of the project, points out, it is a little misleading to compare ETFE with glass.

Although ETFE is widely used as a glass substitute, it makes more sense to use it in an entirely different way. Grimshaw was originally approached by Eden on the basis of Waterloo International Station, and the initial proposals for Eden adopted a similar structure of steel arch trusses and glass. But, says Whalley, 'one benefit of the amount of time it took to get funding, was that it gave us time to think'.

Realisation dawned that the original design was essentially a reworking of Victorian construction techniques. There were concerns about the difficulty of transporting steel and glass to Cornwall, and a feeling that the steel truss structure was inappropriate for a building which was to be irregular in shape. It had always been the plan that the building should hug the contours of the site;

each truss would have to be designed for a specific location, and each would be a different size. This would have been further complicated by the fact that clay was being mined throughout the design process so the profile of the quarry was in a constant state of flux. Each time the quarry changed in shape, the trusses would have to be redesigned.

Whalley had previously investigated the possibilities of lightweight foils, and felt that the team should seek a solution 'that would capitalise on the properties of this ultralightweight material, in a similar way that Loudon's wrought iron did for glass'. The new design was composed of interconnecting spheres, each composed of a hexagonal grid space frame developed in association with the German precision engineering firm Mero.

'The hexagon appears again and again in nature, ' says Whalley. 'Think of flies' eyes or honeycomb. It is the most efficient shape, in that it minimises the tube lengths in comparison with the surface area.' The structure was further refined by introducing an inner layer, which meant that member sizes could be reduced from as much as 500mm in diameter to less than 200mm. At the point where two spheres of different sizes meet, the hexagons change shape to allow members to join the steel arch trusses which form the primary structure linking the domes.

The inspiration for the junction was again found in the natural world: Whalley refers to the way in which dragonflies' wings - lightweight skin composed of a hexagonal cell structure - are connected to the body.

The decision to adopt a more freeform structure made it possible to keep apace of the changing state of the pit: if the sides of the quarry moved, the domes could simply be reduced or increased in size.

The exact position of the biomes was determined by combining a three-dimensional survey of the site topography, undertaken by the engineer Anthony Hunt Associates, with a model mapping the orientation of the sun. The quarry wall was used as one side of each biome, producing a natural terracing effect and a theatrical backdrop for the plants, with the result that the interiors are dramatic even at this early stage when the plants are relatively immature. The overall effect is breathtaking, although some of the details - such as the bamboo handrails - are positively Disneyesque.

The two biomes are joined by 'the link', a low-tech, grass-roofed building which, along with the rammed earth and cedar shingle visitors' centre, was conceived as a complete contrast with the space-age biomes. At present, the link building looks rather ungainly compared to its super-elegant neighbours but, once the grass on the roof has grown and the surroundings are complete, it should blend with the landscape, giving the impression that the biomes are rising out of the ground. There are more buildings in the pipeline: funds are being sought for a third 'arid' biome and for a £12 million stand-alone education centre, and Grimshaw is currently drawing up designs for a 200-bedroom hotel on the site.

Eden, which has already created more jobs than were lost with the closure of the pit, looks set to make a serious impact on Cornwall's regeneration. This - along with the fact that the project is hidden from view - probably explains why the project has faced so little resistance from residents. The main concerns were about the volume of traffic which is likely to hit the local roads.

Whalley insists that the number of cars coming and going will be far lower than at the local Asda, but admits to concerns about whether there will be adequate parking.

Much of the project's support stems from a feeling that it is a grassroots, as opposed to a top-down, initiative. The Eden Project was the brainchild of Tim Smit, the driving force behind the restoration of the nearby Lost Gardens of Heligan. A project which started in 1995 with a £25,000 grant from the Millennium Commission to Tim Smit and Cornish architect Jonathan Ball has metamophosized into a £75 million project. Tim Smit is now the chief executive of Eden. The building has already achieved the iconic status of, say, the Guggenheim in Bilbao, and is in demand as a backdrop for television interviews and adverts. There is no official news that the James Bond crew has been in touch, but all the signs suggest that it will soon be making an appearance at a screen near you.

The biomes are built up from interlocking partial geodesic spheres and clad with ETFE foil cushions. They are accessed via a visitor centre and link structure.

The humid tropics biome spheres range from approximately 25m to 65m radius, forming an enclosed, climatically controlled area of some 1.5ha in plan. The spheres in the Warm Temperate Biome range from approximately 15m to 40m radius and enclose a climatically controlled area of some 0.7ha.

The structural frame of the biomes is a three-dimensional space frame in circular hollow sections. The frame comprises an icosahedral geodesic outer layer with an inner layer of hexagons/pentagons and triangles. The centre points of the outer layer define the hexagons/pentagons of the inner layer, which form triangles under the outer frame nodes. Separation of the two layers is by circular hollow sections connecting the nodes of the hexagons/pentagons.

The frame spans from front to back on to anchored reinforced concrete strip foundations.Structural stability for each of the biomes is afforded by the shell action of the combined intersecting domes, anchored to the foundations by pinned connections.

The roof structure is designed to accommodate the forces and movement due to temperature effects by 'breathing' alone, there are no movement joints within the roof structure.

Around the perimeter of the spheres the inner structural members are brought out to meet the outer members, forming pinned connections to the foundations.

Each biome structure was analysed as a three-dimensional model and subjected to numerous load cases, including several exceptional combinations, such as drifting snow and ponding water. Further nonlinear analysis was undertaken to demonstrate the inherent redundancy in the structure to guard against progressive collapse in these conditions.

The biome link is situated between the humid tropics and the warm temperate biomes. It consists predominantly of two structures within one.

The front roof is of a sloping concave truss system with supporting raking columns at the front utilising the two-storey braced steel frame at the rear for stability. The raking columns have expressed-pinned joints top and bottom. The sloping concave trusses consist of curved top and bottom booms with the internal strut and tie members all pinned jointed.

The two-storey back of house area has a composite concrete deck at first floor level. The roof plane covers the entire link building and is 'warped' at both ends to blend into the surrounding ground. The steel decking supports a green roof system, which forms an integral part of the external landscape.

The main cellular beams are set out on a radial grid, and span between columns generally at 7.5m centres, but increasing closer to the centre of the link. The secondary beams are at 2.75m centres, on both the first and roof level structures.

The visitor centre consists of two single storey buildings. Between the two buildings is a courtyard, partially covered by a fabric roof.

The main building is steel framed, with the roof beams spanning up to 20m between columns.The beams are set out on a radial grid, and slope down, at approximately 5degrees, towards the service building.The roof surface forms part of a shallow cone. The roof is a structural metal deck with insulation and a capping sheet over.

The main access is via a footpath from the car parks to the east. The emergency access road leads to the western end. Both entrances are cut into the hillside with retaining walls required on the southern side.

The stability of the building at each end is provided by columns that cantilever from pad foundations. The central section is loaded laterally by the fabric roof, in addition to the wind load. In this section, a truss system in the plane of the roof transfers the lateral loads to braced frames. The truss members are sized to limit the deflection of the horizontal truss.

The sweeping curve of the building, designed to fit snugly into the site of the pit, made a full three-dimensioned analysis model essential.

CREDITS

CLIENT The Eden Project

CONTRACT VALUE £75 million SIZE 23,000m 2(biomes), site area 15ha,450m end to end

COMPLETION DATE May 2000 (Phase 1) 2001 (full)

PROCUREMENT TYPE Guaranteed maximum price (new engineering contract)

ARCHITECTS Nicholas Grimshaw & Partners: Andrew Whalley, Jason Ahmed, Vanessa Bartulovic, Dean Boston, Jolyon Brewis, Chris Brieger, Vincent Chang, Amanda Davis, Florian Eckardt, Nick Grimshaw, Alex Haw Perry Hooper, William Horgan, David Kirkland, Oliver Konrath, Angelika Kovacic, Quintin Lake, Richard Morrell, Tim Narey, Monica Niggemeyer, Martin Pirnie, Mustafa Salmon, Killian O'Sullivan, Debra Penn, Michael Pawlyn, Juan Porral Hermida, Tan Su Lin Sir Robert McAlpine/Alfred McAlpine Construction

STRUCTURAL ENGINEER Anthony Hunt Associates

STEELWORK CONTRACTOR Mero UK (biomes); Snashalls (visitor centre); Pring & St Hill (biome link)

QUANTITY SURVEYOR Davis Langdon & Everest

SERVICES ENGINEER Arup

PROJECT MANAGER Davis Langdon Management

PROJECT SUPERVISOR Land Architects

PLANNING SUPERVISOR Aspen Burrow Crocker

LANDSCAPE CONSULTANT Land Use Consultants

FIRE CONSULTANT Arup Fire

CLADDING CONSULTANT Arup

ACCESS CONSULTANT Purcell Miller Tritton M+E

SUBCONTRACTOR Colston

SUBCONTRACTORS AND SUPPLIERS ventilation air duct systems; roof and glazing to visitor centre and biome link Allan Roofing & Glazing Systems; horticultural management systems Van Vliet Automation; glass louvres on biomes Levolux A T, M & V, Germany; fixed glazing on biomes Mero/Foiltec (UK Offices); ironmongery Yannedis; waterfall and water features Ritchie MacKenzie; roller shutter doors EDS; scaffolding and scaffold boards John Brash; earth wall to visitor centre In Situ Rammed Earth

WEBLINKS

Eden Project www.edenproject.com

Anthony Hunt Associates www.ahassociates.co.uk

Nicholas Grimshaw & Partners www.ngrimshaw.co.uk

McAlpine Joint Venture www.sir-robert-mcalpine.com

Ove Arup & Partners www.arup.com

Land Use Consultants www.landuse.co.uk

Davis Langdon & Everest www.davislangdon.com

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