ABSTRACT
We report on the collapse of a shallow tunnel during construction. The tunnel was driven according the New Austrian Tunnelling Method (NATM). This case history brings out several important aspects for tunnel construction. First, it shows the importance of interpretation of instrumentation data and the role of numerical analyses in the decision-making process. Second, it reveals the limitation of the observational method for such processes where spontaneous loss of stability is involved. Moderate or even small deformation does not necessarily mean that sufficient safety is still available. Finally, the provision of a contingency plan as the last resort is indispensable for safe tunnel construction.
