BUILDING THE WORLD'S DEEPEST CAR PARK

Australia's most famous landmark is often marvelled at from ground level, but its innovative spiral substructure is a hidden gem

- AILSA HARVEY

Most underground car parks consist of four or five storeys. But beneath the Sydney Opera House there are more than double that, with 12 storeys that extend 37 metres deep. Within this structure, there is space for 1,100 cars to park, serving visitors of both the Opera House itself and the surrounding botanic gardens. It's not only the deepest car park in the world, but the widest shallow-cover rock cavern, too. This means it's the widest underground space that has been evacuated with a relatively thin layer of soil above it. The soil and rock between the car park and ground surface is just seven metres thick, and the cavern spans up to 19 metres wide. The shallower the cover, the more advanced engineering that's required to prevent the structure from collapsing. The original car park design was planned to be rectangular in shape and consisted of two substructures to cover the parking demands of the Opera House. However, this meant valuable space would be taken up to build the two fire escapes needed to meet safe exit requirements in an emergency. This plan radically changed when a circular double-helix design was