Safe & Reliable Tunnels. Innovative European Achievements First International Symposium, Prague 2004 189 ASSESSMENT AND SERVICE LIFE UPDATING OF EXISTING TUNNELS Peter Schiessl, Christoph Gehlen, Gesa Kapteina Ingenieursbüro Professor Schiessl, Germany ABSTRACT This paper highlights the durability assessment (re-design and update) of an existing railway tunnel. This new approach, which has in general been developed within the European Brite- Euram research project DuraCrete 1 and has furthermore been improved within the European research project DARTS 2 , enables the assessment linked to durability considerations of reinforced concrete structures over its service life related to limit state formulations. For the re-design and the update a new full-probabilistic method is being applied, taking tunnel specific conditions into account to assess the reliability of the tunnel lining against carbonation induced corrosion. This design approach has been used first for a bored tunnel construction in The Netherlands, cp. Gehlen and Schiessl 3 . 1. INTRODUCTION Main elements of the service life design of new structures are: Identification of relevant and operational limit states, appropriate deterioration modelling, statistical quantification of material and environmental variables. Relevant information with regard to these items can be summarised and documented for each treated element in a so-called “birth certificate”. As for existing structures detailed information issued within a “birth certificate” usually does not exist, relevant information has to be collected from drawings, tender documents, weather stations, inspections, and other possible sources. Based on the quantification of the collected data the re-design can be carried out. The result of this calculation gives information about the reliability resp. failure probability of the considered element for example against carbonation induced corrosion over its service life. To improve the precision of the re-design the calculation can be updated by incorporating inspection data attained from the structure. In the considered case the information of measured carbonation depth, measured after 15 years of exposure has been used to demonstrate the updating procedure and its influence on the calculated reliability resp. failure probability. Furthermore an assessment based on this calculation result has been carried out to derive information if repair or maintenance action is needed to provide a sufficient reliability over service life according to the requirements given in the EC 1 4 . 2. STRUCTURE AND DECISION PROBLEM The tunnel structure, which is part of a railway express connection, has been build with reinforced concrete. The overall length of the tunnel amounts to l tunnel = 1100 m.