Enhancement of tunnel safety in the Albula railway tunnel

The 5.9 km long Albula railway tunnel is going to be fundamentally refurbished after being in use for more than 100 years. An important reason for the refurbishment is the necessary enhancement of the tunnel's safety measures. Due to the latest developments in the safety standards for railway tunnels, safety aspects such as the disposition and number of emergency exits, the control of the smoke propagation in the case of a tunnel fire, the rescue plan for the passengers, as well as operational measures have to be considered in an early phase of the project. Based on the actual situation, this paper evaluates different refurbishment concepts and the necessity of a ventilation system. The concepts all intend to increase the passenger safety by changing the tunnel profile. Compared to options enlarging the existing tunnel cross-sectional area, the excavation of a new railway tunnel and using the existing tunnel as an escape tunnel offers several advantages. During the excavation of the new tunnel, the train traffic can continue to run in the existing tunnel without any particular constraints. Furthermore, in the final state, the use of the existing tunnel as an escape and rescue tunnel significantly increases the passengers' safety. Ventilation concepts for the railway tunnel as well as for the escape tunnel, providing a safe escape for all passengers, are analysed in the present paper. The smoke propagation in an emergency is mainly influenced by the air speed in the tunnel. The latter is influenced by the climatic conditions at the tunnel portals. As the two tunnels are aerodynamically connected by cross-connections, they cannot be analysed separately. Several ventilation concepts are evaluated using criteria such as the passengers' and operational safety, possibilities of intervention, smoke recirculation, investment and operational costs. According to the detailed comparison, it has been decided to do without a mechanical ventilation system in the railway tunnel. For the escape tunnel ventilation concepts based on an over-pressure are assessed as fundamentally good. As a final result of the safety enhancement measures, the escape tunnel of the Albula will be equipped with an over-pressure ventilation system using ventilation stations at the two portals with one axial fan per station. According to the detailed analyses in the present paper, the optimal ventilation concept in terms of safety as well as for economic reasons could be found for the Albula Tunnel.