The Xi'an trident

After the 2008 Beijing Olympics and the 2010 Shanghai World Exhibition, the International Horticultural Exposition in Xi'an is billed as the third large-scale international event organised to draw worldwide attention to China's ambitions of showcasing green civilisation and promoting its international image. These events also intend to demonstrate China's ability to organise and execute ambitious large-scale urban developments, and in a minimum of time. While in Beijing the focus was on broadcasting the icon, and in Shanghai on displaying innovation, one can argue that the architecture of Plasma Studio for the International Horticultural Exposition is all about intention.

Winners of an invited competition, Plasma Studio designed the exposition's three main buildings: the Exhibition Centre or Theme Pavilion (5,000 square metres), the Greenhouse (4,000 square metres) and the main Guangyun Entrance (3,500 square metres). With offices in Beijing, London and Sesto, Plasma Studio is spearheaded by Eva Castro and Holger Kehne. For the overall execution and planning they collaborated with Groundlab (a landscape firm led by Eva Castro, Holger Kehne and three other partners), Beijing-based LAUR Studio, and the Beijing Institute of Architectural Design (BIAD). "As a competition entry we handed in a sketch," says Holger Kehne, "because we did not have much time. It was more a vision, a collage with bits of information. As we were not satisfied with our proposal, it surprised us to hear we had won. We believed it was a great opportunity to start over again. But we had to stick to what we had initially proposed."

The expo's main entrance is located to the northeast of the site, with half a dozen entry gates leading visitors to a main square. The pavement feels Olympic and orderly, the triangular flowerbeds Arcadian and artificial, while the flowing landscape draws you towards the bridge, which crosses the 60-metre-wide Expo Avenue and offers a panorama of the entire expo site. Rising prominently out of this landscape is the Chinese pagodastyle Chang'an Tower, an observation tower and symbol of the expo. At first it seems that Plasma Studio's other two projects are nowhere to be seen. I spotted the constructions thanks to the queues of people standing outside them.

The bridge performs with the people toing and froing across it, but not on the scale envisaged by the architects, due to an overestimation of the number of visitors. One month into the expo, it was drawing an average of 10,000 visitors per day. This shortfall is being dealt with via a series of white fences that impose a new order over the supposedly seamless system of water, planting, circulation and architecture. "The scale of the project was difficult to grasp," says Holger Kehne. "We were told millions of people would visit, with 200,000 people on peak days. So the flow of people became a big part of the project. As such the potpourri of different elements has been a successful aspect of the design. I am glad that we were able to do this in a ruthless manner, and nobody interfered. I like the colour scheme of the landscape, especially at night."

A large part of any expo visitor's experience is the quality time spent queuing, which amounts to as much as three of four times more than the time spent inside. Waiting in line is hardly most people's prime motivator for going to an expo, but for many it is a reason to go back. It is here that people eat, delete superfluous data and decide where to go next. I looked at the pattern on the floor which leads to the entrance, although not as fast as I was made to believe: makeshift structures make the masses meander.

Located on the edge of the lake as an endpoint to the central axis, the Exhibition Centre is all about corridors and circulation. It also has a few things on display, including a hydroponic installation with bored fish. "We were never given a proper programme for the inside," explains Holger Kehne, "so we did not know what was going on. To us it is all about circulation, flow, openness and adaptation." The building is organised as a massing of three parallel volumes within the landscape, flowing through and underneath it, leading to the piers. Hovering over the lake, the three cantilevered volumes are partially wrapped in bronze, while bands of greenery cover them like a tessellated net. Inside, ramps enable visitors to access a mezzanine level and, in the design's original intentions, also the roof of the building. In the end, however, this architectural ambition was fenced off and the building's roof remains visitor-free.

These and other rearrangements have reduced the spatial experience of the Exhibition Centre to the bare minimum of a loop connecting two large windows. Nonetheless, while the flow and functionality might have disappeared, the pavilion's form and folds stand firm. "There are three large windows for the exhibition, but in the end they put a TV studio in the third wing and closed it off to the public. But the initial idea of the landscraper is still in the building," says Holger Kehne.

The Exhibition Centre ties in with the lake through a series of piers, which is the departure point for the water-crossing by boat. With no naval activity in sight, nor ever to be expected, I decided to cycle to the Greenhouse, and along the way explore the 37-hectare area (about 40 per cent of which is covered by water). The expo terrain features an unsettlingly mediocre collection of pastiche pavilions, made up of dangerously modified architectural species and a few mildly interesting structures. Fortunately there are the flowers, the landscape and a small neighbourhood housing the Afghan, Greek, Burmese, Turkish and Dutch pavilions in close proximity. I was left to wonder who orchestrated this flow of a new horticultural world order. From a distance, the Exhibition Centre looks like a crescent wave, Poseidon's trident or a triclops sea snake. Its straightforward design suggests that architectural labour and thinking was involved, but indeed it feels like a sketch on a napkin.

The Greenhouse clearly aims to be the kind of architecture that sits hidden on the surface of a mountain like a shiny crystal, and from afar it does a good job at it. Up close and queuing, one approaches the building's entrance through a prolonged cut that generates a three-dimensional interweaving of interior and exterior circulation, of building and landscape. Inside, the Greenhouse's horseshoe plan creates a loop that changes in section in order to accommodate a sequence of different planting and spatial conditions. This plan also generates an inner courtyard, making the outside space the natural centre of the building.

"It would be nice to have a more public use for these two buildings after the expo, with a more dense development around them," replies Kehne when asked about the future of the two structures. "Today the area lacks public amenities. It could turn into a central park for the district. Our buildings could facilitate that. They do not have to be turned into an art gallery, but into something more mundane. I would love for the Greenhouse to become a church, and the Exhibition Centre more for exhibitions or performances. We would love to get involved in that and finish the buildings properly. It is not great for the moment, but the buildings are doing their job: they communicate the ambition."

From the colourful cuts in the landscape landscape to the natural pull of the pavement; from the piers of the pavilion to the horseshoe layout that is able to transform scientific knowledge into religious experiences, the space that Plasma Studio has carved out of Xi'an's landscape sets out to be as fluid as the office's name suggests. It is also about sticking to initial ideas and executing their intentions.
—Bert de Muynck, architect and writer, co-director MovingCities

Design architect: PLASMA STUDIO
Eva Castro, Holger Kehne, Ulla Hell
Design team: Eva Castro, Holger Kehne, Mehran Gharleghi, Evan Greenberg, Xiaowei Tong with Tom Lea, Ying Wang, Nicoletta Gerevini, Peter Pichler, Benedikt Schleicher, Ka y Barkan, Danai Sag e, Federico Ruberto
Structural engineering: ARUP (London), John Martin and Associates (Los Angeles)
Design consultants and construction phase lead designers: Beijing Institute of Architectural Design (BIAD)
Landscape design: GROUNDLAB
Eva Castro, Holger Kehne, Sarah Majid, Alfredo Ramirez, Eduardo Rico
Design team (landscape): Eva Castro, Alfredo Ramirez, Eduardo Rico, Jorge Ayala, Hoss ein Kachabi with Nadia Kloster, Steve De Micoli, Elisa Kim, Filipo Nassetti, Rui Liu, Kezhou Chen, Clara Oloriz
Design consultants and construction phase lead designers (landscape): LAUR Studio, Beijing Forestry University
Client: Chan-Ba Ecological District

Site area: 37 ha
Total building area: 12,000 m2
Exhibition Centre: 5,000 m2
Greenhouse: 4,000 m2
Gate building: 3,500 m2
Design phase: 2009
Construction phase: 09/2009—04/2011