The Limfjord Tunnel in Denmark is an immersed tunnel with a total length of 945 m. Construction began in 1965 and the tunnel was inaugurated and opened for traffic in May 1969. The tunnel is unidirectional and consists of two tubes with 3 lanes each. Almost 60,000 vehicles per day pass through the tunnel. Shortly after the tunnel was put into service leakages were observed in tunnel walls and ceilings. By the early 1990s, after 25 years in service, leakages and associated deterioration in the Limfjord Tunnel had reached a stage where overall repair of the structure was needed to ensure and extend its lifetime. A multiple phase repair strategy was adopted to address both structural problems and maintenance and durability problems in the tunnel. The repair period started in 1992 with preliminary works for improving and extending the existing traffic management system. Phase 1 (completed in 1994) included a longitudinal post-tensioning of the tunnel structure to eliminate structural problems and facilitate a durable repair of the severely deteriorating areas in the tunnel. Phase 2 (completed in 1995) included injection of cracks and construction joints to stop leakages through tunnel walls and ceilings. Phase 3 (completed in 1998) included renovation of chloride contaminated concrete and corroded reinforcement in tunnel walls and ceilings. Phase 4 (completed in 1999) included establishing new tunnel equipment and installations such as systems for ventilation, lighting, fire protection of structures and fire control, communication for fire brigade and police, SOS stations, traffic management and monitoring devices, Closed Circuit Video Equipment (CCVE), Incident Detection System (IDS), and new power supply stations including Unbreakable Power Supply (UPS) all related to tunnel safety. The tunnel has now been in full service for traffic for more than 5 years. By looking back over the past 5-10 years, the evaluation of the chosen repair strategy concludes that, post-tensioning has shown its effectiveness and is considered very successful by the owner. The development of new cracks and penetration of salt-laden water through the tunnel structures has been kept to a minimum since 1998. All repaired areas are in good condition after the first 10 years and show no signs of deterioration. Temperature movements are now fully under control. The expected lifetime of the tunnel structure is considered to be in the range of 40-50 years based on experience in Denmark with durability of concrete repairs over the past 30 years. This is on the assumption that the necessary funds will be available and allocated to the tunnel each year for keeping a high level of operation and maintenance. Furthermore, minor repairs are inevitable at times for walls, ceilings, pavements and joints. The existing waterproofing membrane is not considered to be functioning. The lessons learned from the Limfjord Tunnel have been used in the design and construction phases of the immersed Guldborgsund Tunnel (1986) and Oeresund Tunnel (2000) mainly by improving casting technique, concrete technology and waterproofing systems. The total cost of the repairs was approximately 28 million Euro or one fifth the cost of a new tunnel. The repair has caused an increase of 25% in the annual running costs mainly due to new safety equipment and installations. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.