Numerical investigation of the failure of a shotcrete lining

In the course of a 7-km-long railway tunnel, which is situated mainly in weathered chalk marl, covered by Tertiary over a length of about 500 m, the tunnel traverses a transition zone of chalk marl, weathered chalk marl and Tertiary. In a specific area with a length of 100 m, the deformation during tunnel drive did not cease and exceeded the predicted values considerably About one year after the installation of the primary lining, cracks occurred in the shotcrete lining of the invert. Many different geotechnical models have been discussed to explain this special ground behaviour and the failure. Numerical calculations based on extensive geotechnical investigations were performed, aiming at detecting the cause of this failure. It was only when the real ground behaviour and reasons of failure had been understood that the secondary lining could be designed in an optimised way.