what was the london olympic stadium built on
London Stadium The stadium's track and field arena is excavated out of the soft clay found on the site, around which is permanent seating for 25,000, built using concrete "rakers". The natural slope of the land is incorporated into the design, with warm-up and changing areas dug into a semi-basement position at the lower end. Spectators enter the stadium via a podium level, which is level with the top of the permanent seating bowl. A demountable lightweight steel and pre-cast concrete upper tier was built up from this "bowl" to accommodate a further 55,000 spectators.[19]