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Upgrading the Arlberg tunnel to current safety standards
Tunnelling and Underground Space Technology 48 (2015) 140–146
Contents lists available at ScienceDirect
Tunnelling and Underground Space Technology journal homepage: www.elsevier.com/locate/tust
Upgrading the Arlberg tunnel to current safety standards Peter J. Sturm ⇑, Michael Bacher Graz University of Technology, Austria
a r t i c l e
i n f o
Article history: Received 10 September 2014 Received in revised form 10 February 2015 Accepted 23 February 2015 Available online 21 March 2015 Keywords: Road tunnel Upgrading Ventilation system High-pressure water-mist system FFFS TERN
a b s t r a c t Austrian road tunnels within the Trans-European Road Network (TERN) must fulfil the requirements of the Directive 2004/54/EC (European Commission, 2004) not later than April 2019. This regulation has to be applied to all tunnels in the TERN with a length of more than 500 m, whether they are in operation, under construction or at design stage, and aims at ensuring a minimum level of safety for road users. One of the main features of this directive is the requirement for providing an egress possibility to a safe environment every 500 m throughout the whole tunnel. The Arlberg road tunnel has a length of some 15.5 km and is in operation for more than 35 years. It is a single tube tunnel operated with bi-directional traffic, but carries a quite low traffic volume. Hence, the construction of a second tube is not really cost effective. Currently the tunnel is equipped with a transversal ventilation system with remotely controlled smoke extraction dampers providing smoke extraction every 100 m. The maximum distance between egress possibilities to a save environment is some 1500 m. Due to the high costs of a construction of a second tube or a parallel running escape gallery, a novel solution was found. The existing fresh air duct will be used as safe escape way between the existing egress possibilities. This solution has big impacts on the ventilation system and on the requirements for thermal structure protection of the new egress ways, i.e. the fresh air duct. In order to overcome this problem, massive changes in the ventilation design have to be performed, accompanied by the installation of a high-pressure water-mist system for structure protection. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction The Arlberg road tunnel with a length of about 15.5 km is the longest single-tube road tunnel in Austria, operated with bi-directional traffic. The tunnel connects Tyrol and Vorarlberg and is the only winter-safe link between these regions. Due to its importance within the international transport routes it is part of the TransEuropean Road Network (TERN). The average daily traffic volume is about 8000 vehicles/day, peak traffic in holiday seasons is almost twice as high. After 35 years in operation the Arlberg road tunnel must be refurbished. In addition to the required structural refurbishment a lot of upgrading for the electromechanical installations is needed (Bacher and Sturm, 2014) to meet the requirements of the EU directive (European Commission, 2004) and the state of the art of safety systems defined in the Austrian guidelines (RVS 09.02.31, 2014; RVS 09.02.22, 2014). According to the EU directive (European Commission, 2004) the maximum distance between egresses must not exceed 500 m. ⇑ Corresponding author. E-mail address: [email protected] (P.J. Sturm). http://dx.doi.org/10.1016/j.tust.2015.02.006 0886-7798/Ó 2015 Elsevier Ltd. All rights reserved.
The Arlberg railway tunnel runs almost in parallel to the road tunnel. This railway tunnel is part of the Trans-European (Rail) Network (TEN) and had also to fulfil the minimum safety requirements for such railway tunnels. These regulations however require egress possibility to a safe environment every 1.700 m. Already a couple of years ago these egress possibilities were constructed between the rail and the road tunnel with rooms for collecting persons in between (see Fig. 1). The fulfilment of the national and international directives requires a construction of additionally 37 egress ways. An erection of further cross passages between the rail and road tunnel proved to be not cost effective due to the high distance between these two tunnels (up to 300 m). Based on a feasibility study the following solution was chosen. Between the existing cross passages to the railway tunnel the fresh air ducts will serve in future as egress ways. Fig. 1 shows a sketch of the road and railway tunnel as well as of the existing and the new egress ways. Fig. 2 sketches the new egress possibility from the road level up into the egress way in the fresh air duct. To allow also handicapped people to use the egress ways, ramps with a gradient lower equal 10% instead of staircases will be constructed. While the chosen solution minimises construction costs, it does require additional installations for maintaining egress user safety
P.J. Sturm, M. Bacher / Tunnelling and Underground Space Technology 48 (2015) 140–146
141
Fig. 1. Sketch of the egress ways of the Arlberg tunnel. Source: ASFiNAG.
EXHAUST AIR DUCT
FRESH AIR DUCT
EGRESS WAY
Fig. 2. Scheme of the new egress way. Source: ASFiNAG.
and has big implications on existing vital systems like ventilation. In addition special fire protection has to be foreseen for the false ceiling between road and fresh air duct. From various options the installation of a fixed fire-fighting system (FFFS) on basis of a high pressure water mist system was selected to serve for this purpose.
Although the ventilation system has been upgraded around the turn of the century with big smoke extraction dampers to cope with the needs for fire situations additional measures are required for up to date fire ventilation (Sturm et al., 2014).
2. Implications on ventilation
Already currently but also in the coming years ventilation design is driven by the needs for ventilation in incident situations with fire (fire ventilation). The fresh air requirements during normal operation have been decreased during the last years due to the strongly improved emission standards of the vehicles using the tunnel. Hence the driving parameter for ventilation design is the required smoke extraction rate during incidents with fire. The main issue of fire ventilation is the confinement of smoke in the region of the extraction damper (Sturm et al., 2014). Due to the high mountain range between the two portals the Arlberg tunnel represents a weather barrier. Hence meteorological pressure differences between the two portals are quite high. According to the Austrian requirements defined in the RVS 09.02.31 (2014) a 95 percentile value of the barometric pressure differences acting on the portal must be taken into account. Based on the meteorological statistics the 95 percentile of the half-hour mean values amounts to 254 Pa. Massive electro-mechanical
2.1. Current situation The tunnel is currently equipped with a full-transverse ventilation system with six ventilation sections, two vertical shafts (736 m and 218 m) and two portal stations. Each section is currently ventilated by one fresh and one exhaust air fan. Fig. 2 depicts the ventilation scheme, where VS1 to VS6 denote the ventilation sections, F1 to F6 and E1 to E6, denote the fresh and the exhaust air fans (see Fig. 3). Due to the permanent maintenance and service activities the existing axial fans of the ventilation systems are in a quite good shape and need not to be replaced. The fans are quite powerful in pressure increase as well as in volume flow. Hence it can be expected, that they can fulfil also future needs. The fan specifications are given in Table 1.
2.2. Future situation
142
P.J. Sturm, M. Bacher / Tunnelling and Underground Space Technology 48 (2015) 140–146
Fig. 3. Sketch of the existing ventilation scheme of the Arlberg tunnel.
Table 1 Fan specifications of the existing ventilation system. Specification at 1.09 kg/m3 St. Jakob Maienwasen east Maienwasen west Albona east Albona west Langen
Fresh air Exhaust air Fresh air Exhaust air Fresh air Exhaust air Fresh air Exhaust air Fresh air Exhaust air Fresh air Exhaust air
rpm n1/n2 (min F1 E1 F2 E2 F3 E3 F4 E4 F5 E5 F6 E6
490/980
1
)
Number of blades (pcs)
Impeller diameter (m)
Volume flow (m3/s)
Pressure increase (N/m2)
Engine power (kW)
3 3 6 6 6 6 6 6 6 6 6 3
3.162
357 293 363 298 363 298 318 261 318 261 370 304
1859 1532 2694 2224 2779 2154 3148 2251 3023 2361 2004 1930
777 777 1165 777 1165 777 1165 777 1165 777 1165 777
installations in the form of jet fans or air injection nozzles are needed in order to confine the smoke even during situations with high pressure gradients. The installation of jet fans would require either a high amount of small fans (high maintenance costs) or a considerable number of big fans in dedicated ventilation niches (high construction costs). A cost-benefit analysis indicated that usage of the existing fresh air fans for air injection is appropriate. This requires the installation of Saccado type fresh air injection dampers (FAID) and sealing doors within the fresh air duct. Fig. 4 depicts the scheme of the upgraded ventilation system with the FAIDs and three additional jet fans (JF1 to JF3) for smoke control. The related ventilation equipment data is given in Table 2. Fig. 5 depicts the cross-section of the tunnel at the place of the jet-fans. The advantage of this system is that existing fans can be used and structural adaptations
inside the tunnel can be reduced to a minimum. The drawback of FAIDs is that each additional device raises the air volume inside the tunnel. Hence the air/smoke velocity inside the tunnel also increases. Use of a simple jet fan, in contrast, would only produce the required thrust in the traffic room. In order to overcome the problem of increasing volume flow rates, air extraction in other ventilation sections has to be utilised to achieve the required pressure balance (push–pull system Almbauer et al. (2004)). As shown in Fig. 5 the positioning of the jet fans is a little bit challenging. Normally such big fans should be mounted in ventilation niches on both sides of the tunnel. However, in the special case of the Arlberg tunnel it was considered that the opening of the tunnel lining – which would be required for constructing the fan niches – would be too risky and costly due to possible drainage and structural problems. Hence a positioning of the fans at the
Fig. 4. Sketch of the new ventilation scheme of the Arlberg tunnel.
P.J. Sturm, M. Bacher / Tunnelling and Underground Space Technology 48 (2015) 140–146
143
Fig. 5. Sketch of the cross section in the region of jet fan JF1/2/3.
ceiling in the region of the extraction duct proved to be an appropriate solution. However, each constriction of space in the exhaust duct increases the pressure losses during the smoke extraction and reduces its efficiency. In order to minimize these losses, the jet fans were positioned at the very end of the concerned ventilation sections. Special emphasis has been put on the ventilation of the egress ways. While the egress way in the fresh air duct can be pressurized and supplied with fresh air using the existing fresh air supply fans, special emphasis has to be put on the ventilation of the ramps between traffic room and fresh air duct on the one hand and between fresh air duct and collecting rooms at the other hand. While the ramp between traffic room (road level) and fresh air duct will be actively ventilated from the fresh air duct (overpressure), the ramp between collection rooms and fresh air duct will be pressurizes using fresh air from the railway tunnel (see Fig. 6). However in all cases the opening forces need for the egress doors must not exceed 100 N (RVS 09.02.31, 2014). In order to ensure this pressure relief dampers and an electromechanical opening support for the doors have to be installed in each lock.
Table 2 Specifications of the technical data of the ventilation related equipment. Part
Volume flow (m3/s)
Extraction fans see Table 1 E1–E6 Supply fans see Table 1 F1–F6 FAID As fans F2 to F5 Jet fans 66.5
Engine Dimensions Max. power (kW) nominal thrust (N) –
see Table 1
see Table 1
–
see Table 1
see Table 1
–
–
2725
94.5
Length: 3.5 m width: 3.5 m Diameter: 1.8 m length: 4.1 m
2.3. Ventilation control As the tunnel is equipped with a fully transverse ventilation system smoke extraction will be performed by opening remotely controlled dampers in close proximity to the fire location. Smoke will be extracted into the exhaust gas duct. However, smoke confinement needs active control of the air/smoke movement inside the tunnel. A closed loop control system typically consisting of fans as power sources and air velocity sensors inside the tunnel as providers for the control variable. Such a concept was originally implemented in Austria in 2002, using a full closed loop control system for the 10 km long Plabutsch tunnel (RVS 09.02.51, 2014). At that time, however, vertical air injection and extraction was employed without using the momentum of the injected air. Systems with FAIDs have since been applied successfully in Austria in several long road tunnels (Sturm et al., 2008). What is novel in the Arlberg tunnel is the parallel usage of multiple FAIDs and jet fans as well as air extraction in sections other than in the fire section. On basis of numerical simulations fire ventilation scenarios were simulated and the system capability checked. The design fire size for ventilation was chosen in accordance to the Austrian guideline RVS 09.02.31 with a heat release rate of 30 MW. The numerical simulations were performed with a 1D model based on the conservation of mass, momentum and heat (Sturm et al., 2012). Special emphasis was put on the correct simulation of the effect of the FAIDs. Excessive field tests combined with 3D simulations were performed to investigate the local effects of the interaction between air injection and main air flow in the tunnel (Sturm et al., 2013, 2012). Fig. 7 shows such a scenario for a fire in ventilation section VS6. Close to the fire location a mass flow of 144 kg/s smoke/air is to be extracted. In order to achieve a nearly symmetrical flow from both portals towards the extraction location the usage of the FAID1 and
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Fig. 6. Sketch of the egress way and the ventilation related equipment (Bacher and Sturm, 2014).
Fig. 7. Fire ventilation for an incident in ventilation section VS6.
Fig. 8. Sketch of the fan operation mode for a fire scenario in ventilation section VS6.
Fig. 9. Air velocity distribution for an incident in ventilation section VS6.
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Fig. 10. Fresh air injection damper (right) and air lock of the supply duct downstream the FAID (left) Sturm et al. (2012).
Fig. 11. Scheme of the high pressure water mist system.
FAID2 as well as of the jet fans JF1 and JF2 is needed. In addition air extraction is required in section VS6. In this particular case, various exhaust air and fresh air supply fans as well as the jet fans are needed at the same time in order to reach the required ventilation goal. The remaining fresh air fans are needed to vent the escape route via the fresh air duct. For a better understanding Fig. 8 depicts the operation status of the various axial fans. As the fire is located at ventilation section VS6, the fresh air fans F6, F4 and F1 are used for venting the escape routes (light blue). Smoke extraction is performed by fan E6 (red). In order to balance the air/smoke flow in the tunnel the fresh air fans F2 and F3 are used for supplying the FAIDs (dark blue) and the exhaust fan E4 is used for extraction of some air. The jet fans JF1 and JF2 are in operation, JF3 is blocked due to its vicinity to the fire location. The other extraction fans (E1 to E5, except E4) are not in use in this scenario. All relevant parts of the escape routes are vented, except the small regions around the FAIDs 1 and 2. However, as these FAIDs are in operation any access to those regions is blocked in any way. Fig. 9 shows the simulated velocity distribution inside the tunnel resulting from fan activation in this scenario. As it can be seen, the ventilation goal with symmetrical air flow from both sides of the incident location towards the extraction point can be achieved. Fig. 10 shows as an example a FAID in the fresh air duct of the Katschbergtunnel in Austria and the movable door downstream the FAID which acts as an air lock in the supply duct in case of active FAID operation. In addition it acts as separation between escape route and ventilation related object.
3. Fire protection of the structure The erection of an egress way close to a possible fire source at road level poses the requirement of special protection of the structure. Various measures for structure protection are available. Starting from application of fire resistant slabs to installation of water based systems. In the current project a high pressure water mist system will be installed to protect the intermediate ceiling – and thus the fresh air duct which serves as an emergency escape – against high temperature in the traffic room of the Arlberg road tunnel. High pressure water mist systems have proven to be an effective mean for fire suppression (Lakkonen at al., 2014). The high pressure water mist system enables the water mist to penetrate into a fire in liquid form and result in cooling due to evaporation at specific locations. High pressure water mist also effectively fills up the protected space and provides superior cooling, hence protecting surrounding equipment and structures. The influences on ventilation – mostly in terms of reduced heat release rate – have already been investigated in detail, e.g. Rothe et al. (2014). The increase in volume due to evaporation of water is counteracted by the reduction in volume due to the reduction in heat. Hence the influence of a water mist system on the extraction capacity of the ventilation system is not considered to be severe. The installation of such a system for structure protection in Austria is not unique (Köll, 2008). Nevertheless the combination of tunnel length, geographical position within the Alps and space constraints due to the existing tunnel poses a big challenge for designing, installing and operation such a system.
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The requirement for action as structure protection is given in the Austrian guideline (RVS 09.01.45, 2006). In this special case the system must be able to cope with a pool fire with a size of 100 m2 (this accounts to a heat release rate of roughly 200 MW). Basic design parameters are given in the Austrian guideline RVS 09.02.51 (2014). The system has to be designed in order to operate over a time of 120 min. An Aqueous Film Forming Foam (AFFF) is used to coat the fuel, preventing its contact with oxygen, resulting in suppression of the combustion (see Fig. 11). The operation of the ventilation system is not influenced by any operation of the water mist system and vice versa, both control mechanisms must operate in parallel and independently from each other. 4. Conclusion The 15.5 km long Arlberg road tunnel has to be refurbished to fulfil the requirements posed in the EU directive on minimum safety of road tunnels (European Commission, 2004) as well as to be upgraded with safety equipment according to the Austrian state of the art (RVS 09.02.31, 2014; RVS 09.02.22, 2014). The construction of additional egress ways is the main objective of the required works. The upgrading of the existing Arlberg tunnel has to be done under the focus of limitations in civil works and time until April 2019. As this tunnel constitutes a major link within a winter-safe connection in the Austrian and Trans European road network special emphasis on the organisation of the refurbishment work has to be put. In order to keep the down time of the tunnel short and to minimize construction costs the fresh air duct will be used as an egress way. Thus the construction of long cross-passages to the parallel running railway tunnel can be avoided. Hence the project has to utilise as much existing equipment as possible avoiding new constructions of major civil works. In case of fire tunnel users can reach the fresh air duct (safe area) via ramps from the traffic room. From the fresh air duct the egress ways lead to existing collecting rooms, from where the tunnel users will be evacuated through the railway tunnel. With this option the overall costs for refurbishment will be minimized. However, this calls for quite complex changes in the existing ventilation scheme and moreover in the operation of such a complex system. A combination of air extraction by external axial fans, jet fan operation and Saccardo type air injection will be required in order to control the air/smoke movement inside the tunnel in case of a fire. As the fresh air duct above the traffic room will be used as egress way additional structure protection of the false ceiling is required. This will be done by installation of a high pressure water mist system. With such a system it is possible to reduce the heat
release rate of a fire source as well as the radiative heat transfer due to effective cooling. It has to be considered that the most challenging issue in the design and operation of the ventilation system is the quite high barometrical pressure gradient between the two portals. As the Austrian guideline requires the consideration of the 95 percentile of the meteorological conditions for the Arlberg tunnel, there exist still a considerable amount of hours, during which the ventilation system might not be able to fully achieve its purpose. References Almbauer R.A., Sturm P., Bacher M., Pretterhofer G., 2004. Simulation of ventilation and smoke movement. In: Proceedings of the 2nd Symposium on Tunnel Safety and Ventilation, Graz, Austria, 19–21 April 2004, pp. 32–38. ISBN: 3-90135195-7. Bacher M., Sturm P., 2014. Upgrading existing road tunnels in the TERN to current needs, taking the Arlberg tunnel as an example. In: Proceedings of the 7th Symposium on Tunnel Safety and Ventilation. Graz, Austria, pp. 90–100. ISBN: 978-3-85125-320-7. European Commission, 2004. Directive 2004/54/EC of the European Parliament and of the Council on Minimum Safety Requirements for Tunnels in the Trans European Road Network, 29th April 2004. Köll M., 2008. Single tunnel and still safe. In: Proceedings of the 4th Symposium on Tunnel Safety and Ventilation, Graz, Austria, pp. 133–138. ISBN: 978-3-85125008-4. Lakkonen M., Sprakel D., Feltmann D.A., 2014. Comparison of deluge and water mist systems from a performance and practical point of view. In: Proceedings of the 7th Symposium on Tunnel Safety and Ventilation, Graz, Austria, pp. 203–212, ISBN: 978-3-85125-320-7. Rothe R., Lakkonnen M., Sprakel D., 2014. Improving ventilation and passive protection with FFFS. In: Proceedings of the 7th Symposium on Tunnel Safety and Ventilation, Graz, Austria, pp. 195–202. ISBN: 978-3-85125-320-7. RVS 09.01.45, 2006. Tunnel, Tunneling, Constructional Fire Protection in Transportation Buildings for Roads. Forschungsgemeinschaft Straße, Schiene, Verkehr, Wien. RVS 09.02.22, 2014. Tunnel, Tunnel Equipment, Operation and Safety Equipment. Forschungsgemeinschaft Straße, Schiene, Verkehr, Wien. RVS 09.02.31, 2014. Tunnel, Tunnel Equipment, Ventilation, Basic Principles. Forschungsgemeinschaft Straße, Schiene, Verkehr, Wien. RVS 09.02.51, 2014. Tunnel, Tunnel Equipment, Fixed Fire Extinguishing Systems. Forschungsgemeinschaft Straße, Schiene, Verkehr, Wien. Sturm P., Bacher M., Brandt R., 2008. Evolving needs of tunnel ventilation in a changing world. In: Proceedings of the 4th Symposium on Tunnel Safety and Ventilation, Graz, Austria, 21–23 April 2008, pp. 8–21. ISBN: 978-3-85125-0084. Sturm P., Beyer M., Bacher M., Schmölzer G., 2012. The influence of pressure gradients on ventilation design – special focus on upgrading long tunnels. In: Proceedings of the 4th Symposium on Tunnel Safety and Ventilation, Graz, Austria, 23–25 April 2012, pp. 90–99. ISBN: 978-3-85125-210-1. Sturm P., Beyer M., Bacher M., 2013. Consideration of a Saccardo nozzle system for tunnel ventilation applications – a simple calculation method for a one dimensional approach. In: 15th International Symposium on Aerodynamics, Ventilation & Fire in Tunnels, Barcelona, Spain, 18–20 September 2013, pp. 105–119 (BHR group 2013). Sturm P., Bacher M., Wierer A., 2014. Strategies for fire ventilation. In: Proceedings from the Sixth International Symposium on Tunnel Safety and Security, Marseille, France, 12–14 March 2014.
Contents lists available at ScienceDirect
Tunnelling and Underground Space Technology journal homepage: www.elsevier.com/locate/tust
Upgrading the Arlberg tunnel to current safety standards Peter J. Sturm ⇑, Michael Bacher Graz University of Technology, Austria
a r t i c l e
i n f o
Article history: Received 10 September 2014 Received in revised form 10 February 2015 Accepted 23 February 2015 Available online 21 March 2015 Keywords: Road tunnel Upgrading Ventilation system High-pressure water-mist system FFFS TERN
a b s t r a c t Austrian road tunnels within the Trans-European Road Network (TERN) must fulfil the requirements of the Directive 2004/54/EC (European Commission, 2004) not later than April 2019. This regulation has to be applied to all tunnels in the TERN with a length of more than 500 m, whether they are in operation, under construction or at design stage, and aims at ensuring a minimum level of safety for road users. One of the main features of this directive is the requirement for providing an egress possibility to a safe environment every 500 m throughout the whole tunnel. The Arlberg road tunnel has a length of some 15.5 km and is in operation for more than 35 years. It is a single tube tunnel operated with bi-directional traffic, but carries a quite low traffic volume. Hence, the construction of a second tube is not really cost effective. Currently the tunnel is equipped with a transversal ventilation system with remotely controlled smoke extraction dampers providing smoke extraction every 100 m. The maximum distance between egress possibilities to a save environment is some 1500 m. Due to the high costs of a construction of a second tube or a parallel running escape gallery, a novel solution was found. The existing fresh air duct will be used as safe escape way between the existing egress possibilities. This solution has big impacts on the ventilation system and on the requirements for thermal structure protection of the new egress ways, i.e. the fresh air duct. In order to overcome this problem, massive changes in the ventilation design have to be performed, accompanied by the installation of a high-pressure water-mist system for structure protection. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction The Arlberg road tunnel with a length of about 15.5 km is the longest single-tube road tunnel in Austria, operated with bi-directional traffic. The tunnel connects Tyrol and Vorarlberg and is the only winter-safe link between these regions. Due to its importance within the international transport routes it is part of the TransEuropean Road Network (TERN). The average daily traffic volume is about 8000 vehicles/day, peak traffic in holiday seasons is almost twice as high. After 35 years in operation the Arlberg road tunnel must be refurbished. In addition to the required structural refurbishment a lot of upgrading for the electromechanical installations is needed (Bacher and Sturm, 2014) to meet the requirements of the EU directive (European Commission, 2004) and the state of the art of safety systems defined in the Austrian guidelines (RVS 09.02.31, 2014; RVS 09.02.22, 2014). According to the EU directive (European Commission, 2004) the maximum distance between egresses must not exceed 500 m. ⇑ Corresponding author. E-mail address: [email protected] (P.J. Sturm). http://dx.doi.org/10.1016/j.tust.2015.02.006 0886-7798/Ó 2015 Elsevier Ltd. All rights reserved.
The Arlberg railway tunnel runs almost in parallel to the road tunnel. This railway tunnel is part of the Trans-European (Rail) Network (TEN) and had also to fulfil the minimum safety requirements for such railway tunnels. These regulations however require egress possibility to a safe environment every 1.700 m. Already a couple of years ago these egress possibilities were constructed between the rail and the road tunnel with rooms for collecting persons in between (see Fig. 1). The fulfilment of the national and international directives requires a construction of additionally 37 egress ways. An erection of further cross passages between the rail and road tunnel proved to be not cost effective due to the high distance between these two tunnels (up to 300 m). Based on a feasibility study the following solution was chosen. Between the existing cross passages to the railway tunnel the fresh air ducts will serve in future as egress ways. Fig. 1 shows a sketch of the road and railway tunnel as well as of the existing and the new egress ways. Fig. 2 sketches the new egress possibility from the road level up into the egress way in the fresh air duct. To allow also handicapped people to use the egress ways, ramps with a gradient lower equal 10% instead of staircases will be constructed. While the chosen solution minimises construction costs, it does require additional installations for maintaining egress user safety
P.J. Sturm, M. Bacher / Tunnelling and Underground Space Technology 48 (2015) 140–146
141
Fig. 1. Sketch of the egress ways of the Arlberg tunnel. Source: ASFiNAG.
EXHAUST AIR DUCT
FRESH AIR DUCT
EGRESS WAY
Fig. 2. Scheme of the new egress way. Source: ASFiNAG.
and has big implications on existing vital systems like ventilation. In addition special fire protection has to be foreseen for the false ceiling between road and fresh air duct. From various options the installation of a fixed fire-fighting system (FFFS) on basis of a high pressure water mist system was selected to serve for this purpose.
Although the ventilation system has been upgraded around the turn of the century with big smoke extraction dampers to cope with the needs for fire situations additional measures are required for up to date fire ventilation (Sturm et al., 2014).
2. Implications on ventilation
Already currently but also in the coming years ventilation design is driven by the needs for ventilation in incident situations with fire (fire ventilation). The fresh air requirements during normal operation have been decreased during the last years due to the strongly improved emission standards of the vehicles using the tunnel. Hence the driving parameter for ventilation design is the required smoke extraction rate during incidents with fire. The main issue of fire ventilation is the confinement of smoke in the region of the extraction damper (Sturm et al., 2014). Due to the high mountain range between the two portals the Arlberg tunnel represents a weather barrier. Hence meteorological pressure differences between the two portals are quite high. According to the Austrian requirements defined in the RVS 09.02.31 (2014) a 95 percentile value of the barometric pressure differences acting on the portal must be taken into account. Based on the meteorological statistics the 95 percentile of the half-hour mean values amounts to 254 Pa. Massive electro-mechanical
2.1. Current situation The tunnel is currently equipped with a full-transverse ventilation system with six ventilation sections, two vertical shafts (736 m and 218 m) and two portal stations. Each section is currently ventilated by one fresh and one exhaust air fan. Fig. 2 depicts the ventilation scheme, where VS1 to VS6 denote the ventilation sections, F1 to F6 and E1 to E6, denote the fresh and the exhaust air fans (see Fig. 3). Due to the permanent maintenance and service activities the existing axial fans of the ventilation systems are in a quite good shape and need not to be replaced. The fans are quite powerful in pressure increase as well as in volume flow. Hence it can be expected, that they can fulfil also future needs. The fan specifications are given in Table 1.
2.2. Future situation
142
P.J. Sturm, M. Bacher / Tunnelling and Underground Space Technology 48 (2015) 140–146
Fig. 3. Sketch of the existing ventilation scheme of the Arlberg tunnel.
Table 1 Fan specifications of the existing ventilation system. Specification at 1.09 kg/m3 St. Jakob Maienwasen east Maienwasen west Albona east Albona west Langen
Fresh air Exhaust air Fresh air Exhaust air Fresh air Exhaust air Fresh air Exhaust air Fresh air Exhaust air Fresh air Exhaust air
rpm n1/n2 (min F1 E1 F2 E2 F3 E3 F4 E4 F5 E5 F6 E6
490/980
1
)
Number of blades (pcs)
Impeller diameter (m)
Volume flow (m3/s)
Pressure increase (N/m2)
Engine power (kW)
3 3 6 6 6 6 6 6 6 6 6 3
3.162
357 293 363 298 363 298 318 261 318 261 370 304
1859 1532 2694 2224 2779 2154 3148 2251 3023 2361 2004 1930
777 777 1165 777 1165 777 1165 777 1165 777 1165 777
installations in the form of jet fans or air injection nozzles are needed in order to confine the smoke even during situations with high pressure gradients. The installation of jet fans would require either a high amount of small fans (high maintenance costs) or a considerable number of big fans in dedicated ventilation niches (high construction costs). A cost-benefit analysis indicated that usage of the existing fresh air fans for air injection is appropriate. This requires the installation of Saccado type fresh air injection dampers (FAID) and sealing doors within the fresh air duct. Fig. 4 depicts the scheme of the upgraded ventilation system with the FAIDs and three additional jet fans (JF1 to JF3) for smoke control. The related ventilation equipment data is given in Table 2. Fig. 5 depicts the cross-section of the tunnel at the place of the jet-fans. The advantage of this system is that existing fans can be used and structural adaptations
inside the tunnel can be reduced to a minimum. The drawback of FAIDs is that each additional device raises the air volume inside the tunnel. Hence the air/smoke velocity inside the tunnel also increases. Use of a simple jet fan, in contrast, would only produce the required thrust in the traffic room. In order to overcome the problem of increasing volume flow rates, air extraction in other ventilation sections has to be utilised to achieve the required pressure balance (push–pull system Almbauer et al. (2004)). As shown in Fig. 5 the positioning of the jet fans is a little bit challenging. Normally such big fans should be mounted in ventilation niches on both sides of the tunnel. However, in the special case of the Arlberg tunnel it was considered that the opening of the tunnel lining – which would be required for constructing the fan niches – would be too risky and costly due to possible drainage and structural problems. Hence a positioning of the fans at the
Fig. 4. Sketch of the new ventilation scheme of the Arlberg tunnel.
P.J. Sturm, M. Bacher / Tunnelling and Underground Space Technology 48 (2015) 140–146
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Fig. 5. Sketch of the cross section in the region of jet fan JF1/2/3.
ceiling in the region of the extraction duct proved to be an appropriate solution. However, each constriction of space in the exhaust duct increases the pressure losses during the smoke extraction and reduces its efficiency. In order to minimize these losses, the jet fans were positioned at the very end of the concerned ventilation sections. Special emphasis has been put on the ventilation of the egress ways. While the egress way in the fresh air duct can be pressurized and supplied with fresh air using the existing fresh air supply fans, special emphasis has to be put on the ventilation of the ramps between traffic room and fresh air duct on the one hand and between fresh air duct and collecting rooms at the other hand. While the ramp between traffic room (road level) and fresh air duct will be actively ventilated from the fresh air duct (overpressure), the ramp between collection rooms and fresh air duct will be pressurizes using fresh air from the railway tunnel (see Fig. 6). However in all cases the opening forces need for the egress doors must not exceed 100 N (RVS 09.02.31, 2014). In order to ensure this pressure relief dampers and an electromechanical opening support for the doors have to be installed in each lock.
Table 2 Specifications of the technical data of the ventilation related equipment. Part
Volume flow (m3/s)
Extraction fans see Table 1 E1–E6 Supply fans see Table 1 F1–F6 FAID As fans F2 to F5 Jet fans 66.5
Engine Dimensions Max. power (kW) nominal thrust (N) –
see Table 1
see Table 1
–
see Table 1
see Table 1
–
–
2725
94.5
Length: 3.5 m width: 3.5 m Diameter: 1.8 m length: 4.1 m
2.3. Ventilation control As the tunnel is equipped with a fully transverse ventilation system smoke extraction will be performed by opening remotely controlled dampers in close proximity to the fire location. Smoke will be extracted into the exhaust gas duct. However, smoke confinement needs active control of the air/smoke movement inside the tunnel. A closed loop control system typically consisting of fans as power sources and air velocity sensors inside the tunnel as providers for the control variable. Such a concept was originally implemented in Austria in 2002, using a full closed loop control system for the 10 km long Plabutsch tunnel (RVS 09.02.51, 2014). At that time, however, vertical air injection and extraction was employed without using the momentum of the injected air. Systems with FAIDs have since been applied successfully in Austria in several long road tunnels (Sturm et al., 2008). What is novel in the Arlberg tunnel is the parallel usage of multiple FAIDs and jet fans as well as air extraction in sections other than in the fire section. On basis of numerical simulations fire ventilation scenarios were simulated and the system capability checked. The design fire size for ventilation was chosen in accordance to the Austrian guideline RVS 09.02.31 with a heat release rate of 30 MW. The numerical simulations were performed with a 1D model based on the conservation of mass, momentum and heat (Sturm et al., 2012). Special emphasis was put on the correct simulation of the effect of the FAIDs. Excessive field tests combined with 3D simulations were performed to investigate the local effects of the interaction between air injection and main air flow in the tunnel (Sturm et al., 2013, 2012). Fig. 7 shows such a scenario for a fire in ventilation section VS6. Close to the fire location a mass flow of 144 kg/s smoke/air is to be extracted. In order to achieve a nearly symmetrical flow from both portals towards the extraction location the usage of the FAID1 and
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Fig. 6. Sketch of the egress way and the ventilation related equipment (Bacher and Sturm, 2014).
Fig. 7. Fire ventilation for an incident in ventilation section VS6.
Fig. 8. Sketch of the fan operation mode for a fire scenario in ventilation section VS6.
Fig. 9. Air velocity distribution for an incident in ventilation section VS6.
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Fig. 10. Fresh air injection damper (right) and air lock of the supply duct downstream the FAID (left) Sturm et al. (2012).
Fig. 11. Scheme of the high pressure water mist system.
FAID2 as well as of the jet fans JF1 and JF2 is needed. In addition air extraction is required in section VS6. In this particular case, various exhaust air and fresh air supply fans as well as the jet fans are needed at the same time in order to reach the required ventilation goal. The remaining fresh air fans are needed to vent the escape route via the fresh air duct. For a better understanding Fig. 8 depicts the operation status of the various axial fans. As the fire is located at ventilation section VS6, the fresh air fans F6, F4 and F1 are used for venting the escape routes (light blue). Smoke extraction is performed by fan E6 (red). In order to balance the air/smoke flow in the tunnel the fresh air fans F2 and F3 are used for supplying the FAIDs (dark blue) and the exhaust fan E4 is used for extraction of some air. The jet fans JF1 and JF2 are in operation, JF3 is blocked due to its vicinity to the fire location. The other extraction fans (E1 to E5, except E4) are not in use in this scenario. All relevant parts of the escape routes are vented, except the small regions around the FAIDs 1 and 2. However, as these FAIDs are in operation any access to those regions is blocked in any way. Fig. 9 shows the simulated velocity distribution inside the tunnel resulting from fan activation in this scenario. As it can be seen, the ventilation goal with symmetrical air flow from both sides of the incident location towards the extraction point can be achieved. Fig. 10 shows as an example a FAID in the fresh air duct of the Katschbergtunnel in Austria and the movable door downstream the FAID which acts as an air lock in the supply duct in case of active FAID operation. In addition it acts as separation between escape route and ventilation related object.
3. Fire protection of the structure The erection of an egress way close to a possible fire source at road level poses the requirement of special protection of the structure. Various measures for structure protection are available. Starting from application of fire resistant slabs to installation of water based systems. In the current project a high pressure water mist system will be installed to protect the intermediate ceiling – and thus the fresh air duct which serves as an emergency escape – against high temperature in the traffic room of the Arlberg road tunnel. High pressure water mist systems have proven to be an effective mean for fire suppression (Lakkonen at al., 2014). The high pressure water mist system enables the water mist to penetrate into a fire in liquid form and result in cooling due to evaporation at specific locations. High pressure water mist also effectively fills up the protected space and provides superior cooling, hence protecting surrounding equipment and structures. The influences on ventilation – mostly in terms of reduced heat release rate – have already been investigated in detail, e.g. Rothe et al. (2014). The increase in volume due to evaporation of water is counteracted by the reduction in volume due to the reduction in heat. Hence the influence of a water mist system on the extraction capacity of the ventilation system is not considered to be severe. The installation of such a system for structure protection in Austria is not unique (Köll, 2008). Nevertheless the combination of tunnel length, geographical position within the Alps and space constraints due to the existing tunnel poses a big challenge for designing, installing and operation such a system.
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The requirement for action as structure protection is given in the Austrian guideline (RVS 09.01.45, 2006). In this special case the system must be able to cope with a pool fire with a size of 100 m2 (this accounts to a heat release rate of roughly 200 MW). Basic design parameters are given in the Austrian guideline RVS 09.02.51 (2014). The system has to be designed in order to operate over a time of 120 min. An Aqueous Film Forming Foam (AFFF) is used to coat the fuel, preventing its contact with oxygen, resulting in suppression of the combustion (see Fig. 11). The operation of the ventilation system is not influenced by any operation of the water mist system and vice versa, both control mechanisms must operate in parallel and independently from each other. 4. Conclusion The 15.5 km long Arlberg road tunnel has to be refurbished to fulfil the requirements posed in the EU directive on minimum safety of road tunnels (European Commission, 2004) as well as to be upgraded with safety equipment according to the Austrian state of the art (RVS 09.02.31, 2014; RVS 09.02.22, 2014). The construction of additional egress ways is the main objective of the required works. The upgrading of the existing Arlberg tunnel has to be done under the focus of limitations in civil works and time until April 2019. As this tunnel constitutes a major link within a winter-safe connection in the Austrian and Trans European road network special emphasis on the organisation of the refurbishment work has to be put. In order to keep the down time of the tunnel short and to minimize construction costs the fresh air duct will be used as an egress way. Thus the construction of long cross-passages to the parallel running railway tunnel can be avoided. Hence the project has to utilise as much existing equipment as possible avoiding new constructions of major civil works. In case of fire tunnel users can reach the fresh air duct (safe area) via ramps from the traffic room. From the fresh air duct the egress ways lead to existing collecting rooms, from where the tunnel users will be evacuated through the railway tunnel. With this option the overall costs for refurbishment will be minimized. However, this calls for quite complex changes in the existing ventilation scheme and moreover in the operation of such a complex system. A combination of air extraction by external axial fans, jet fan operation and Saccardo type air injection will be required in order to control the air/smoke movement inside the tunnel in case of a fire. As the fresh air duct above the traffic room will be used as egress way additional structure protection of the false ceiling is required. This will be done by installation of a high pressure water mist system. With such a system it is possible to reduce the heat
release rate of a fire source as well as the radiative heat transfer due to effective cooling. It has to be considered that the most challenging issue in the design and operation of the ventilation system is the quite high barometrical pressure gradient between the two portals. As the Austrian guideline requires the consideration of the 95 percentile of the meteorological conditions for the Arlberg tunnel, there exist still a considerable amount of hours, during which the ventilation system might not be able to fully achieve its purpose. References Almbauer R.A., Sturm P., Bacher M., Pretterhofer G., 2004. Simulation of ventilation and smoke movement. In: Proceedings of the 2nd Symposium on Tunnel Safety and Ventilation, Graz, Austria, 19–21 April 2004, pp. 32–38. ISBN: 3-90135195-7. Bacher M., Sturm P., 2014. Upgrading existing road tunnels in the TERN to current needs, taking the Arlberg tunnel as an example. In: Proceedings of the 7th Symposium on Tunnel Safety and Ventilation. Graz, Austria, pp. 90–100. ISBN: 978-3-85125-320-7. European Commission, 2004. Directive 2004/54/EC of the European Parliament and of the Council on Minimum Safety Requirements for Tunnels in the Trans European Road Network, 29th April 2004. Köll M., 2008. Single tunnel and still safe. In: Proceedings of the 4th Symposium on Tunnel Safety and Ventilation, Graz, Austria, pp. 133–138. ISBN: 978-3-85125008-4. Lakkonen M., Sprakel D., Feltmann D.A., 2014. Comparison of deluge and water mist systems from a performance and practical point of view. In: Proceedings of the 7th Symposium on Tunnel Safety and Ventilation, Graz, Austria, pp. 203–212, ISBN: 978-3-85125-320-7. Rothe R., Lakkonnen M., Sprakel D., 2014. Improving ventilation and passive protection with FFFS. In: Proceedings of the 7th Symposium on Tunnel Safety and Ventilation, Graz, Austria, pp. 195–202. ISBN: 978-3-85125-320-7. RVS 09.01.45, 2006. Tunnel, Tunneling, Constructional Fire Protection in Transportation Buildings for Roads. Forschungsgemeinschaft Straße, Schiene, Verkehr, Wien. RVS 09.02.22, 2014. Tunnel, Tunnel Equipment, Operation and Safety Equipment. Forschungsgemeinschaft Straße, Schiene, Verkehr, Wien. RVS 09.02.31, 2014. Tunnel, Tunnel Equipment, Ventilation, Basic Principles. Forschungsgemeinschaft Straße, Schiene, Verkehr, Wien. RVS 09.02.51, 2014. Tunnel, Tunnel Equipment, Fixed Fire Extinguishing Systems. Forschungsgemeinschaft Straße, Schiene, Verkehr, Wien. Sturm P., Bacher M., Brandt R., 2008. Evolving needs of tunnel ventilation in a changing world. In: Proceedings of the 4th Symposium on Tunnel Safety and Ventilation, Graz, Austria, 21–23 April 2008, pp. 8–21. ISBN: 978-3-85125-0084. Sturm P., Beyer M., Bacher M., Schmölzer G., 2012. The influence of pressure gradients on ventilation design – special focus on upgrading long tunnels. In: Proceedings of the 4th Symposium on Tunnel Safety and Ventilation, Graz, Austria, 23–25 April 2012, pp. 90–99. ISBN: 978-3-85125-210-1. Sturm P., Beyer M., Bacher M., 2013. Consideration of a Saccardo nozzle system for tunnel ventilation applications – a simple calculation method for a one dimensional approach. In: 15th International Symposium on Aerodynamics, Ventilation & Fire in Tunnels, Barcelona, Spain, 18–20 September 2013, pp. 105–119 (BHR group 2013). Sturm P., Bacher M., Wierer A., 2014. Strategies for fire ventilation. In: Proceedings from the Sixth International Symposium on Tunnel Safety and Security, Marseille, France, 12–14 March 2014.