Collapse of tunnels: soil-structure interaction failures Professor Robert Mair Cambridge University Engineering Department

Tunnelling with shield and rings.

New Austrian tunnelling method New Austrian tunnelling method. Sprayed concrete lining onto unsupported walls.

Conclusions Tunnel collapses usually catastrophic Soil-structure interaction important in tunnel lining design – time-dependent soil pressures depend on stiffness of lining Shape is critical: ‘horseshoe’ tunnel lining vulnerable to structural failure – Toulon Sprayed concrete vulnerable to construction defects in lining – eventual instability – Heathrow