Evaluation of trends in tunnel lining utilization with regards to the moment of ring closure

At sequenced tunnel drives, next to the rock mass conditions, the advance rates of the single excavation stages and the moment of ring closure determine the performance of shotcrete linings. Especially in heterogeneous rock masses, the investigation of the optimum ring closure moment resulting in no damage of the lining challenges the engineers. If the ring closure is too early, the lining may experience compressive failure because the building up of ground loads is too large. A late ring closure may allow for too much tunnel displacement. To investigate the effects of various ring closure moments on the utilization of the tunnel lining and the tunnel crown convergences, this study performs 3D finite element simulations. The results at a specific measuring cross section and for the assumed ground conditions suggest that a delayed ring closure can lead to higher utilizations compared to an early ring closure.