EQUALLY AS challenging as the roof is the engineering needed where the arch meets the ground. As with any arch, when you load it up its feet want to 'kick out'.
Given the size of the Wembley roof, the forces being exerted on the foundations are enormous - 17.5 MN horizontal thrust.
To resist them, Mott MacDonald has designed two huge concrete bases - 40 m by 25 m by 3 m thick - supported on 40 massive 1500 mm-diameter, 25 m-long piles. The horizontal thrust from the arch is resisted by passive resistance from the soil and bending of the piles.
'The best system to have would be a tie between the feet of the arch, ' says David Satchell. 'Clearly that was not possible, so the arch is built on two independent foundations.'
Mr Satchell says the interface between the base of the arch and the foundations is every bit as complex as the roof/PPT interface (above).
'I wouldn't wish the interaction between the soil and the structure on anyone, ' he says. 'There is some really amazing engineering going on there.'