Monitoring and modeling ground deformations during tunnelling

Monitoring of ground deformations in tunnelling is a principal means for selecting the appropriate excavation and support methods among those foreseen in the design, for ensuring safety during tunnel construction (including personnel safety inside the tunnel and safety of structures located at ground surface) and, finally, for ensuring construction quality management according to ISO 9000. This paper briefly describes the types of ground deformation measurements often used in tunnelling, the difficulties in obtaining ground measurements and their subsequent evaluation, and the application of these measurements (a) in modeling tunnel excavation and support and (b) in establishing early warning systems against incipient ground collapses or damage to structures at ground surface. Examples of ground deformation monitoring and their application in tunnel design and construction are illustrated via cases from the Jubilee Line Extension of the London Underground, from Lines 2 and 3 of the Athens Metro and from a nine-kilometer long mountain tunnel in Greece. In the first two examples, ground deformation monitoring aimed to ensure that structures at ground surface would not be harmed by the tunnelling operations. In the third case, the objective was the optimization of the temporary support requirements as well as early warning against potential collapses. 1