Prediction of stress‐induced tunnel collapses based on displacement monitoring

Abstract Brittle fault zones in Alpine regions are typically characterised by pronounced heterogeneity, resulting in highly variable stress distributions and displacement patterns within the surrounding rock mass and the underground structure. These conditions frequently lead to significant face instabilities, overbreaks and collapses during tunnelling. A systematic analysis of several Alpine tunnel projects has revealed a correlation between the occurrence of such incidents when the excavation approaches a relatively stiff rock mass section. Notably, the transition towards zones of increased rock mass stiffness can be predicted by observing the longitudinal displacements and/or displacement vector orientation. Findings of this research highlight that these displacement trends serve as potential early indicators of an impending stress‐induced tunnel collapse and thus enable the proactive adjustment of excavation and support measures. Numerical simulations confirmed these findings. This approach helps to avoid dangerous, costly and time‐consuming rehabilitation works and increases the safety of the crew.