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A cave-in failure in a headrace tunnel in Buon Kuop, Vietnam, is analysed using convergence confinement (CC-method) and 2D numerical modelling (Phase 2). Results from the application of the former method show the method to be useful in parametric studies used to estimate the rock mass properties and to confirm that an appropriate failure criterion is used. The results from the analyses indicated that properties obtained by observing and classifying the material in the weakness zone may replace in situ tests during the pre-investigation phase of a tunnel design program. The results also indicated that non-linear failure criteria, such as the Hoek–Brown rock mass strength criterion, are suitable for analysing the particular problem. The rock mass properties and the recommended failure criterion were used in 2D numerical analyses that highlighted the caving mechanism. Excavation and support measures were also modelled. Even though the methods produced results that match, reasonably, the in situ behaviour, limitations concerning groundwater and support properties are highlighted.
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