THE HEATHROW-EXPRESS TRIAL TUNNEL

The Heathrow Express project will provide a high speed rail link into Heathrow Airport, and includes two stations to be constructed at the airport in bored tunnels. The Paper describes the NATM trial tunnel built as part of the project. The first section of the Paper gives the principle reasons for the choice of NATM and for the construction of the trial tunnel. It includes details of the tunnel design and of the extensive instrumentation installed. The methods of construction and durations of the main activities are described and discussed. The second section concentrates on the information available from the ground monitoring installed around the tunnel. Movements at and below the existing ground surface are summarized and presented in various graphical formats to facilitate comparison with current standard methods of settlement prediction and to allow trends to be established. General conclusions are drawn which it is hoped will be of value in the prediction of ground movements for future NATM tunnels in similar geology.