Construction of the A20 Round Hill tunnels, Kent

摘要

The two 400 m long road tunnels which now carry the A20 through Round Hill in Kent — part of a £65 million improvement scheme associated with the UK Channel Tunnel terminal — are seen by many as a milestone in the history of British tunnelling. The environmental sensitivity of the area resulted in the UK's first road tunnel to be designed and built following the basic philosophy of the New Austrian Tunnelling Method (NATM). Despite unexpectedly poor ground conditions, the method of incremental support and observation proved a success, with movements of the surrounding chalk being less than anticipated. This paper describes the construction of the tunnels and makes particular reference to environmental and safety issues.