DESIGN AND CONSTRUCTION OF THE A20 ROUND HILL TUNNELS

This article reports on a British Tunnelling Society meeting where the first use of the New Austrian Tunnelling Method (NATM) on a UK road tunnel was described and discussed. The tunnels, which form part of the A20 improvement between Folkestone and Dover, are each 380m long, accomodate 2 lanes of traffic and an emergency walkway, and are constructed on a 3.5% decline through Lower Chalk. Presentations by the consultant and contractor gave details of the geology of the area, spilling, excavation techniques, primary and secondary support, machinery used and in-tunnel monitoring. The discussion which followed focussed on various aspects of NATM.