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A framework with a robust design of the driving classes is fundamental for the tunnel design. During tunnel advance, the detailed design of the lining is depending on the documented geology and the observed system behaviour. To reduce costs, the excavation profile is optimized with the aim of reducing overbreaks and shotcrete masses. This achieved profile accuracy is beneficial for the load‐bearing capacity of the rock and the shotcrete lining. For temporary and permanent tunnel shotcrete linings, the excavation profile accuracy influences the stress distribution, the crack pattern and the expected deformations. In the course of this study, the effect of the excavation geometry on the load‐bearing capacity of the primary lining of drill and blast tunnels was examined. For this purpose, shotcrete linings, reinforced by steel meshes and fibre‐reinforced linings, were compared in optimized and non‐optimized scanned excavation cross‐sections. In each case, an ultimate load and failure analysis was carried out to assess shells in the hardened state by means of numerical modelling (ATENA). The aim is to determine the load‐bearing capacity of the shell structure in order to obtain a conclusion regarding its structural robustness. The interaction between the rock/soil soil and the structure as well as a time‐dependent material behaviour were not considered. It could be shown how an irregular overbreak or an inconsistent shell thickness has a negative effect on the load‐bearing capacity of the structure. [ABSTRACT FROM AUTHOR]

Material efficient tunnel segments with hybrid reinforcement – Design, fabrication, and experiments Load introduction zones of tunnel lining segments are subject to high local stresses. This applies in particular to the attachment locations of the jacks and the longitudinal joints as the contact points between the individual segments in ring direction. Usually, the partial area loading of the longitudinal joint dominates dimensioning of the entire segment; however, apart from this, it is not fully utilized. Two potential solutions are developed in this article. One strengthens the load‐bearing capacity of the longitudinal joints in the area of load introduction by the use of high‐strength concrete and hybrid reinforcement of steel bars and steel fibers. The rest is still made of normal strength concrete. Casting of concrete is matched to this; upright and hybrid. Alternatively, segments made of high‐strength concrete throughout but with recesses are developed. Corresponding designs are implemented on large scale in the lab and tested for their load‐bearing capacity. In both cases, it is with around 75 % and 86 %, respectively, significantly higher than that of a conventional reference segment. There are also potential savings of around 35 % in terms of CO2 equivalents. In addition, the lower segment thickness required reduces the excavation cross‐section, which brings cost benefits. [ABSTRACT FROM AUTHOR]

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