Owing to increasing traffic and the need for constructing second tunnel tubes including corresponding cross-passages, where only one tube existed thus far, sampling of tunnel-lining materials with an age of 30–40 years has been made possible. Laboratory and in situ tests were carried out to evaluate the long-term effects of the tunnel linings. This paper presents the outcomes regarding the long-term behavior of support elements and membranes after performing strength tests on inner and outer lining concrete samples, flat jack tests, rock bolt tests, and tests on re-extracted sheet membranes, as well as geotextiles.

Furthermore, the interface connection mechanical behavior in a double-shell-lined tunnel was investigated with laboratory tests. The aim of this research was to determine the characteristics of sheet membranes and geotextiles in the case of reduced load-bearing capacity caused by degradation of the primary lining. The results provide information on the load-sharing effects of the interaction between the primary and secondary lining, depending on the waterproofing sheet membrane and geotextile properties.

Based on the results, conclusions for new design approaches for underground infrastructure construction can be formulated.