Tunnels within primary road networks are complex systems. The prerequisite of a good level of service is the seamless interaction of the various tunnel components (structural elements and technical equipment). Due to their heterogeneous nature, electrical and structural components are subject to divergent aging processes which require recurring maintenance procedures and rehabilitation measures. Considering the diversity of specifications and requirements among electrical/mechanical and structural components, it is evident that there is a considerable mismatch of maintenance cycles among them. Hence, tunnel asset management faces the challenge to develop strategies to integrate both the necessary functional integrity of the individual components over their respective lifecycle and the requirement of an optimized management for the overall system. Yet, the synchronization of measures towards maximizing system availability must not contradict positive wear‐and‐tear contingencies of the various tunnel components. Evidence based forecasting and reliability centred decision models are key elements of modern life cycle management. They must include interdependencies between the diversity of components and their manifold maintenance cycles.

Regular structural assessments of tunnel linings are commonly performed by visual inspection. Crack phenomena and their development over time are essential indicators of changes of the stress regimen. These are the most prominent input data for the structural assessment of linings. Cladding for fire protection or noise control inhibit visual inspection and call for alternative methods of crack detection and monitoring. This paper presents the application of an alternative method which employs distributed fibre optic sensing (DFOS) which is installed on already existing linings. The objective is to obtain monitoring results with best reliability in comparison to conventional inspection. While the application of DFOS with fibres embedded in new linings has already been tested extensively, later installation on existing linings poses various challenges. Based on findings obtained from laboratory and field tests in an operational highway tunnel, we found that by means of later installed fibres with lengths of up to 70 m, strain measurements can achieve accuracies of about 1 µm/m over 10 mm. This allows the detection of both current and historical crack widths at 0.01 mm precision, conspicuous strain patterns and temperature abnormalities. The system can be mounted onto the inner lining surface which is covered by later claddings and are hence inaccessible to visual inspection. The structural performance can eventually be inferred from interpreted crack patterns.

Pressure tunnels with pre‐stressed concrete linings are recognised as state‐of‐the‐art technology. Numerous pre‐stressed concrete linings, featuring diameters of up to 6 m, have been successfully implemented over the last few decades.This paper on the Niagara Tunnel Facility Project (NTFP) illustrates how the concept of passive pre‐stressing can be further developed for application in increasingly complex geometrical and geotechnical boundary conditions. The diversion tunnel with an excavation diameter of 14.4 m was advanced in horizontal layers of sedimentary rock, which are characterised by a wide range of strengths and anisotropic stiffnesses as well as by pronounced time‐dependent deformation behaviour. The in‐situ stress field is marked by an exceptionally high horizontal stress, which s several times greater than the overburden pressure. The ground has a considerable swelling potential and is highly aggressive to concrete. This combination of difficult geotechnical conditions and unusual structural dimensions poses an unprecedented challenge to the designers with respect to both the design of the pre‐stressed final lining and the planning of the grouting works. The long‐term behaviour is modelled with the help of higher‐order creep and shrinkage laws, which are calibrated based on trials and measurements.Druckstollen mit vorgespannter Betonauskleidung stellen einen anerkannten Stand der Technik dar. Für passiv vorgespannte Druckstollenauskleidungen liegt eine Vielzahl an langjährigen Erfahrungen für Durchmesser bis 6 m vor.Dieser Beitrag erläutert anhand des Beispiels des Niagara Tunnel Facility Projects (NTFP), wie das Konzept der passiven Vorspannung auf geometrisch wie geotechnisch ungewöhnliche Rahmenbedingungen erweitert werden kann. Der Umleitungstunnel mit einem Ausbruchdurchmesser von 14,4 m wurde in einer horizontalen Wechselfolge von Sedimentgesteinen vorgetrieben, die eine große Bandbreite an Festigkeiten und anisotropen Steifigkeiten sowie ein ausgeprägtes zeitabhängiges Verformungsverhalten aufweisen. Das Primärspannungsfeld ist charakterisiert durch ungewöhnlich hohe Horizontalspannungen, die ein Vielfaches des Überlagerungsdrucks betragen. Es besteht ein ausgeprägtes Quellpotenzial sowie ein stark betonaggressives Milieu. Die Kombination aus schwierigen geotechnischen Verhältnissen mit ungewöhnlichen Bauwerksdimensionen, stellt den Entwurf der vorgespannten Innenschale vor eine bislang unbekannte Herausforderung hinsichtlich Dimensionierung und Planung der Verpressarbeiten. Das Langzeitverhalten wird mithilfe höherwertiger Kriech‐ und Schwindgesetze abgebildet, die anhand von Versuchen und Messungen kalibriert wurden.

Sustainability is a guiding principle for political, economic and ecological action, which in companies, societies and countries all over the world, is based on the following three pillars: ecology, economy and social aspects. With the associated worldwide efforts to reduce emissions, this topic has also arrived in the construction industry in general and thus in tunnel construction in particular. In addition to the actual planning, construction, use and maintenance of mined structures, tunnel builders certainly have a special role to play, since the creation of underground structures relieves overground structures and can also change living space for the better. However, the influences and impact must always be considered in the overall context of all three pillars of sustainability – and in our fast‐paced times, this requires a considerable change in mindset as well as a clear change and expansion of the assessment standards. The following article draws a current picture of “sustainable tunnelling” on the basis of four sub‐sections that describe selected tasks and approaches from the perspective of operators, planners, the construction industry and science as a basis for discussion.

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