TRICKY TUNNELLING on Turkey's Kizla Tunnel was concluded last Thursday with the final breakthrough after 10 years work on the Tarsus to Gaziantep motorway.
Two major collapses slowed work on this tunnel - one of 10 three lane bores, totalling 10km. Tunnels alternate with spectacular viaducts to carry the road through the Toros mountains.
Bores were driven through a complex mix of sandstone, siltstone, mudstone and limestone in an active seismic zone. Ground support relied on reinforced shotcrete - the New Austrian Tunnelling Method.
Designer in the design and build tunnelling contract is Geoconsult, which also acted for the contractor on the Heathrow Express NATM tunnels.
Mud rushed in 'like wet concrete' when the tunnel collapsed in December 1995, according to chief tunnel supervisor Robin Clay. Joint venture contractor Tekfen-Impresit and its Polish tunnelling subcontractor Kopex controlled the collapse by grouting loose ground. Drill and blast excavation was restarted 'very slowly' only to suffer a second collapse in April 1996.