<P> On 13 October 2006, London Organising Committee of the Olympic and Paralympic Games confirmed that it had selected Sir Robert McAlpine and Populous to start exclusive negotiations with, to fulfil the eventual design and build contract of the new Olympic Stadium after no other organisations met the bidding criteria . The stadium design was launched on 7 November 2007 . </P> <P> The construction of the stadium commenced three months early in May 2008 after the bowl of the stadium had been dug out and the area cleared . The building of the stadium was completed in March 2011 reportedly on time and under budget, with the athletics track laid in October 2011 . </P> <P> 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 . </P> <P> The stadium is made up of different tiers; during the Games the stadium was able to hold 80,000 spectators . The base tier, which allows for 25,000 seats, is a sunken elliptical bowl that is made up of low - carbon - dioxide concrete; this contains 40 percent less embodied carbon than conventional concrete . The foundation of the base level is 5,000 piles reaching up to 20 metres (66 ft) deep . From there, there is a mixture of driven cast in situ piles, continuous flight auger piles, and vibro concrete columns . The second tier, which holds 55,000 seats, is 315 m (1,033 ft) long, 256 m (840 ft) wide, and 60 m (197 ft) high . The stadium contains just under a quarter of the steel as the Olympic Stadium in Beijing for the 2008 Summer Olympics, approximately 10,700 tonnes (11,800 short tons). In addition to the minimal use of steel, which makes it 75 percent lighter, the stadium also uses high - yield large diameter pipes which were surplus on completion of North Sea Gas pipeline projects in its compression truss, recycled granite, and many of the building products were transported using trains and barges rather than by lorry . </P>

What was the london olympic stadium built on