They excavated 56,234 metric tonnes (62,000 tons) of soil and shale before pouring a 6.71 m (22 ft) deep concrete and steel foundation on a hand-and-machine-smoothed shale base. The foundation is designed to carry the weight of the tower and its contents. The construction process involved more than 10,800 individual pieces of heavy equipment including bulldozers, draglines, backhoes, and cranes. The largest piece of equipment used was a 200-tonne (220 tons) crane. A team of 40 people worked on the foundation for two and a half years non-stop, 12 hours a day, 5 days a week. They used earthmoving equipment to break up hard rock beneath the site in order to create an even surface for the foundation. The foundation is designed to carry the weight of the tower and its contents - which include four major exhibition spaces, three restaurants, a theatre, a science centre, a hotel, a shopping mall, a public park, and a landscaped rooftop with viewing galleries and gardens. If the foundation were to fail, it would cause the building to collapse. The foundation is the deepest in North America. It can carry approximately 7% of the total weight of the structure, or 70,000 tonnes (77,000 tons).