HEATHROW EXPRESS NATM TRIAL TUNNEL

At a total of about found235 million, there is to be a new high- speed rail link between the Paddington terminal in central London and Heathrow Airport, which will provide a 16-minute non-stop journey, almost four times as fast as the present public transport route. This article describes the tunnels that this new railway will require, and gives details of the construction of one of these tunnels, being used as a trial site for the New Austrian Tunnelling Method (NATM). Most of the route from Paddington will use existing tracks, but the line will then branch south into a section using 5.5km of twin tunnels, running under the M4 motorway to an underground station serving Heathrow Terminals 1, 2 and 3. From there, a 2km long single tunnel, accommodating services in both directions, will continue to an underground terminus station below Terminal 4. The single tunnel is being used for the NATM trial, because the complex shapes and wide openings, required in the Heathrow Express stations, do not suit the relatively inflexible modular segment system being used in the twin tunnels. A feasibility study showed that NATM would save substantial time and money, and the trial tunnel has been designed specifically to show NATM's advantages and provide more information relevant to its use.