The award-winning 120,000m2 BA Waterside building near Heathrow Airport houses up to 3,000 people. Such a high population means an enormous car parking requirement. Buro Happold's solution was to put the car park on two levels beneath the building - a solution that may seem more appropriate to a confined city centre site.
'Taking parking into subterranean levels is normally accepted as an expensive way of creating vehicular storage space,' comments Buro Happold group director Nick Nelson. 'However, in this instance the 60,000m2 of underground car parking was a justified environmental solution, given that the site has been totally reclaimed from a previous waste tip.
'The clean site development strategy for this heavily contaminated area necessitated the excavation of 700,000m3 of contaminated material from a 'saucer' covering the entire development.'
A raft foundation avoids differential settlements along the layout of the sophisticated basement structure. Groundwater from the three rivers on the site are effectively kept out by an encircling clay bund. As well as this, a perimeter drainage system ensures the basement is dry and floatation is avoided.
'A friendly environment in the underground car park is encouraged by some natural daylighting, a technique that has become a Buro Happold speciality,' says Nelson. Daylight enters the spaces through large gratings which open into the landscaped gardens that surround the complex above.
Shafts of sunlight entering the underground space play a key role in the atmosphere of the parking complex. The introduction of natural daylight allows the two floors to avoid the oppressive, slightly sinister atmosphere that can at times pervade underground parking areas.
BA Waterside is a concrete frame of considerable horizontal scale. This brings issues of massive concrete slab areas settling, hydrating, creeping, cooling and warming according to climatic conditions and the slow process of the building settling and drying out. Engineering solutions put into practice in the car park area to resolve these problems include designing elliptical columns, arranged to suit parking layout. These have been designed to include a sliding bearing joint in the column head to absorb movement.
Buro Happold also researched and developed a special light-coloured concrete mix for the building A combination of standard Portland cement, ground granulated blastfurnace slag and pale aggregates improves shrinkage behaviour, as well as giving the fine light finish required by Norwegian architect Neils Torp.