Stadelhofen Station

Located in the heart of Zurich on Stadelhofen Square, the new station will be the first rapid-transit system to be built in Switzerland and was intended to become the key inner-city node. The program call for the accommodation of a third track and the creation of a commercial arcade. but because of the challenges posed by the site, the project was far behind schedule. The station was to be built in a dense urban area between Stadelhofen Square and the Hohenpromenade Hill, once a bastion of the old city's fortifications. In collaboration with Arnold Amsler and Werner Rüegger, the competition's initial design proposed access to the platforms through a sub-terranean passage, which can be reached only from the old station building.

To ease the passenger flow, this design was altered to provide stairs and escalators to each side of the old building. The station was thus transformed into a linear environment, where trains can be approached quickly from all directions. Options for accommodating a third track were a tunnel (the more intricate but less intrusive approach) and an open excavation (the quicker solution). Calatrava proposed a compromise that respected the terrain but could be implemented without delay. He demolished the old retaining wall, undercut the slope and retained the hill with a concrete box-beam with convex soffit, supported at the rear by an anchored and piled wall and supported by a series of slanting, tapering, triple-point columns at the front.

This structure develops as a continuous section following the curve of the tracks under the hill. Above the box-beam, running its full length, is a promenade, enhanced by a cable trellis to create a green 'canopy'. Travelers coming to the station from this side reach the platforms via stairs or elevator, or cross to the other side of the tracks via bridges. A road bridge follows the gradient of the hill; a pedestrian bridge is supported by a triangulated structure; and a second pedestrian bridge springs like a thin, undulating membrane of concrete from a distinctive sculptural base. Covering the open platform is a curved canopy made of translucent glass, which allows light to filter down to the sub-terranean passageway through prefabricated glass-brick elements laid in the platform. The client wanted to connect the underground passages to create a shopping precinct. Concrete supports were cast in place using one-piece formwork, which was moved and adjusted to the gradient for each new casting.

The exposed concrete ceiling appears to be two separate elements that meet at the center but it is actually one continuous, undulating surface. Despite the complexity of its shape, this ceiling proved to be cheaper to build than a suspended structure. The need to close the station at night resulted in the development of hydraulically activated devices to shut the entrances and in some cases protecting it from the weather.