Abstract

A serious cave-in in the Buon Kuop headrace tunnel in Vietnam is analysed. The tunnel is 60 m deep, in young sedimentary rocks. A 15–20 m wide weakness zone cuts across the tunnel, causing the cave-in and a sinkhole. This article focuses on comparison between 2D and 3D models. Both models are able to include adverse conditions in the tunnel such as poor rock mass, overburden and groundwater. The tunnel failure is well reflected by both models. There are some differences between the models. The 2D model is user friendly, fast, but requires assumptions to model the spiling bolts, the steel rib, or the contribution of the tunnel wall. The 3D model can include many details such as "umbrella" effect of the spiling bolts and the associated supports of embedded steel ribs. Forces on bolts and its deformations are studied. Deformation around the tunnel is slightly different between the models.

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