wtc 2011 paper fire protection in tunnels

8/3/2019 WTC 2011 Paper Fire Protection in Tunnels

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Underground spaces in the service

of a sustainable society

ITA-AITESWorld Tunnel Congress

and 37th General Assembly

May 21-26, 2011

Helsinki, Finland


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Fire Protection in Tunnels:

Requirements, Solutions and Case histories

Frank Clement, MEYCO Global Underground Construction, Division of BASF ConstructionChemicals Zurich, Switzerland, [email protected]

A. Focaracci , Prometeoengineering.it srl, Rome, Italy

Keywords:concrete spalling, fire protection options, polypropylene fibres, passive fire protection.

1. Design life

The modern, reliability-based service life design for tunnels is implemented in most new designsand in re-design of existing structures and has been adopted by national authorities and individualclients in countries all over the world. Currently there are no real standards on how to designconcrete for a specific design life. The current concrete codes are recommending various mixdesigns and reinforcement cover for design life of approx. 50 yearsTunnels are now usually designed for a service life of 100, 120 or even 200 years. This by farsurpasses the assumed design life according to most codes and standards. All uncertaintiesregarding, the designer has to take into account environmental exposure, material properties anddeterioration modelling in order to meet the required design life.Thus service life design, based on functional requirements, can be carried out by sticking to thesame mechanical concept as the one that is used for structural design. Other issues that need tobe considered in relation to the required design life are water tightness of the lining and itsbehaviour under a fire. Both will influence the design life of a permanent concrete tunnel lining. By

design concrete with high durability the designer should also consider the behaviour of theconcrete during a tunnel fire and in some cases this behaviour is negatively influenced by theconcrete mix properties and the used materials.

2. Precast segments

Excavations of tunnels using an EPB or slurry TBM are requiring a high volume of segments.These segments are produced in specialized precast plants. Advantages of precast plants are thespeed of production in a controlled working environment ensuring constant quality of the concretesegment. Most precast plants use computer controlled systems for the batch and mixingequipment with automatic moisture control of the aggregates. This leads to a better quality,homogeneous mix with fewer variations in workability and strength [1].

In order to comply with the required design life, sometimes more than 100 years, higher structuralperformances and increased durability of precast structures are necessary. This is requiring aoptimal use of the materials and production techniques. State of the art admixtures are used in theconcrete to provide specific performances in the fresh, hardening and hardened stage for eachapplication. Casting, compaction and curing are carried out in controlled circumstances. Thisallows the concrete to reach the required performances at a very early stage in the most efficientmanner. It is now possible to produce precast concrete elements having compressive strengthgrade higher than 100 MPa.

All precast producers have specific requirements and the aim is to produce elements in the mostcost effective manner but still complying with the national and international norms and the required

life time. To achieve this objective, the precast concrete producer must optimize his productionprocess; reduce material, labour and energy costs. In this process he may opt for a daily turnaround of the casting beds using relatively long curing cycles or he may opt for two or more


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production cycles per day. The main factor which controls the production cycle is the compressivestrength required for de-moulding, eventual pre-stress transfer and handling of the elements. Therequirements for compressive strength may vary from 20 MPa for ordinary reinforced concreteelements, to up to 45 MPa for certain pre-stressed concrete structures. Superplasticisers arecommonly used to enhance the workability of the fresh concrete for easy placement and to lowerthe water cement ratio for increasing the strength using relatively low cement content. Heat curing

(steam or electrical) is often used to accelerate the strength development for releasing the bed forthe successive cycle.

Typically, a precast process includes designing and producing a concrete mixture to achievespecific properties such as high early strengths, placing the concrete in the forms, heat or ambientcuring (depending upon the climatic conditions) of the concrete elements, removal from the formsand handling of the elements during transport and erection. In a state of the art plant the placingand consolidation of concrete is facilitated by utilizing the new generation of superplaticizersbased on PCEs ( Poly Carboxylic Ethers) and efficient vibration. Heat curing is normally applied toobtain the required strengths at the desired early age.

The PCE polymers of the second generation (Admixture Controlled Energy, Glenium ACE) have

been designed according to a specific balance between the negatively charged carboxylic groupsand the hydrophilic side chains placed along the backbone in a specific molecular configuration.

The mechanism of action is based on the hypothesis that the polymers are adsorbed onto thecement particles and leave a greater free surface exposed to water for hydration while maintainingthe dispersion effect. This effect leads to a faster activation of the hydration as compared to othersuperplasticizers. This leads to early evolution of heat and rapid strength development.

Furthermore, the adsorption of this new polymer affects mainly the unhydrated cement and veryslightly the hydration products. For this reason, the crystallization reaction is activated in advanceand not delayed by further adsorption of the superplasticizer molecules. The early development ofthe heat of hydration can further activate or accelerate the hydration of the cement. Therefore, theenergy usually furnished from an external source (steam or electric heating) is internally activatedby this new type of PCE molecule. In order to reach the required development of strength with the

specific cement type, the PCE superplasticizer tests have to confirm the compatibility of thecement with the PCE. The compressive strengths development for cements A, B and C aresummarizes in the table below. All concrete batches were prepared and cured at sametemperature.

Cement Type A Cement Type B Cement Type CTime 16 hr 18 hr 16 hr 18 hr 16 hr 18 hrStandardPCE

17,6N/mm

21 N/mm 19,4N/mm

27,9N/mm

8,7 N/mm 14 N/mm

GleniumACE type

41,2N/mm

45,9N/mm

41,3N/mm

47,6N/mm

35,5N/mm

40,7N/mm

Table 1: Concrete strength development with different admixtures and cement types

Figure 1: mechanism of new generation of admixtures


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Admixture systems have to be tailored to meet the individual needs of the precast producer. It canbe used for optimizing the heat curing cycle, increase production by reducing the curing time,elimination of heat curing, elimination of vibration or a combination of any of these parameters.

2.1 Precast tunnel segments example:Railway link Bologna - Florence

The high speed railway link between Bologna and Florence is a twin shaft tunnel of 6000 m lengtheach made with a Tunnel Boring Machine (TBM). The final lining of the tunnel is with precastconcrete segments of 40 cm thickness and a length of 1, 50 m. Each ring, of 16, 40 m volume, iscomposed of 7 segments plus one base element that will support the rail track. The plant is acarousel type designed to produce 126 segments corresponding to 18 rings, each day. To meet thespecifications regarding cement type and content, maximum curing temperature and minimumcompressive strength at demoulding, a mix with cement content of 380 kg/m of CEM IV/A 42.5Rand ACE type superplasticiser was adopted. The consistence class is S1 because of the mouldconfiguration and curing chamber temperature, maintained by the hydration of cement, is 50C.The strengths at the time of demoulding at 6 hrs are above 25 MPa. This allows 3 elements to beproduced each day with the same mould, thus obtaining increased productivity with the right choseof mix design and admixtures.

2.2 Precast tunnel segments example:Tunnel lining segments in U.K. for the ChannelTunnel Rail Link

Carousel casting method using concrete with acement/fly ash blend (310/110 kg/m3) and steelfibres was employed. Glenium ACE 30 was usedin order to achieve a water cement ratio of 0,36and a slump of 60mm. The segments were curedat 35-40C for six hours. The averagecompressive strength was 70 MPa at 28 days.About 300 rings were produced each week [2].

3. Concrete behaviour under a fire load

Clients and designers are increasing the required design life of tunnels by using high quality, denseconcrete. Due to there low permeability these type of concretes resists to severe environmental

exposure. On the other hand during a fire these concretes can be subject to spalling, resulting in areduction of the durability and service life of the structure.Despite the benefits of its non-combustibility and low thermal diffusivity, low permeable concreteswill have the tendency to spall at lower temperatures. Concrete suffers from two problems during afire:

Deterioration in mechanical properties (particularly above 300C) (Explosive) spalling

The spalling of concrete is unpredictable and a number of factors are influencing this phenomenon.[3]

3.1 Fire load

First we have to consider the influence of the fire like: Heating rate: a fast temperature increase is resulting stresses and tensions in the concrete. Maximum temperature: in a tunnel fire typical temperatures of 1100C to 1400C can be

Figure 2: segment production plant


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reached Duration of the fire

3.2 Concrete Composition

If we consider the materials the following properties have an influence Permeability

The permeability is influenced by the cement type, water cement ratio and the use of fillers likesilica fume. With the new types of superplasticizers lower water cement ratio, even below 0,35, areused resulting in concrete with a low permeability.

Aggregate type and sizeDifferent types of aggregates have different thermal expansion coefficients which lead to stressesin the concrete while it is heated. Also the maximum size will influence the spalling behaviour.

Moisture contentConcrete has always some water inside which is physical bonded in the pores. Depending on theenvironment the amount of pore water is fluctuating. If this pore water is heated the pressure caneasily reach 100MPa. Modelling is showing that there is a big influence on the pressure betweendry and wet concrete.

With the close pore model estimations of the pressure can be calculated assuming an equilibriumbetween liquid and gas phase of the water in the pores.

With increase temperature the pressure in the pores will increase depending on the filling degreewith water.

Liquid water

Air + water gas

Liquid water

Air + water gas

Figure 3: closed pore model

Figure 4: influence of temperature on pore pressure


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3.3 Structural properties

It does not to be highlighted that the geometry, compressive loading, supports and restrainedexpansion will have an influence on the spalling behaviour since they will induce additionalstresses in the concrete

3.4 Application

We should not forget the way of casting which caninfluence the spalling behaviour as experienced in a testdone by Efectis the Netherlands.This test is showing thedifference in spalling behaviour of the same concreteduring the same fire test. The panel was castedhorizontal and one plate was tested with casting sidedown and the other one with mould side down. The onewith the mould side down was spalling more severe. Thistest is illustrating that although concrete has the same

composition, spalling can be influenced by the way ofcasting. Influences like moulds, vibration and stability ofthe mix should not be underestimated.

4. Fire protection

To date, the criteria for passive fire protection has been in practice to determine a thickness ofthermal insulation to limit the interface temperature below a critical level. This interface criticaltemperature limit criterion is insufficient to protect the concrete against spalling because theheating rate (i.e. rate of temperature increase) has a greater influence upon the occurrence ofspalling than the temperature level itself. So another criterion should be considered, in replacementof, or in addition to the critical temperature criterion, namely the critical heating rate criterion [4] [5].

4.1 Current Status of Tunnel Fire Protection

As a consequence of several notable fires, including the latest ones in the Frejus road tunnel,South of France and the last fire in the Channel tunnel last year, the European understanding ofthe problems associated with the safety of tunnels in fires has improved dramatically. A number ofresearch programs have been started soon after the year 2000 [6], and are finalized their findings

through the EU funded SafeT project, which are translated into mandatory national and regionalrequirements under the EU Directive platform that will be of considerable benefit to the tunneloperators and travelling public.Currently in Europe national requirements are adopted. Furthermore since 2005, recentrefurbishment projects of major road tunnels in Europe have required wholesale upgrade of thesafety features in the tunnel (emergency lighting, escape routes, warning systems, active fireprotection systems etc). This is clearly set to continue this year, and the coming years.

In other regions of the world the picture is less developed, except for Japan, Australia andSingapore which are similar to Europe in terms of project driven specifications and requirements.North America interest in the role of passive fire protection is increasing, particularly in part being

due to the number of European design teams working on tunnel contracts, coupled withestablished European contractors who are in joint ventures with American companies.

Figure 5: influence of casting on spalling behaviour


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4.2 Structural Issues

As mentioned above, the better the quality of concrete, the worse it performs under fire. Designersare asking more and more for high durable concrete in order to have a structure with a life time ofmore then 100 years. In order to achieve this high durability requirement, concretes are designedto have a low permeability. But this high durable concrete with a low permeability will have a higher

risk of spalling. This was dramatically evident with the Channel Tunnel fire in November 1996, withalmost complete loss in concrete lining section from a train fire.When concrete tunnel linings are exposed to fire there are structural issues to be considered [7]:

1. The concrete typically undergoes explosive spalling, and will continue to do so untilthere is no concrete left, or the fire diminishes

2. The concrete is heated to high temperatures and loses structural strength3. If the structure contains active steel reinforcement, then loss in tensile strength occurs

at high temperatures4. Due to the temperature gradient and different expansion rate of the constituents of the

concrete, deformation cracks and fissure will appear in the concrete.

To demonstrate the structural loss in strength of concrete and reinforcement steel, see figure 6.

Clearly, the role of a passive fire protection system is to ultimately protect the concrete from all theissues described above. As can be seen from figure, maintaining the structural concrete below300C in the event of hydrocarbon or cellulose fires prevents all negative structural issues formoccurring.Finally, to conclude this brief insight, the rate of heating is also crucial, and has a dramatic effect onthe spalling mechanism. Thermal shock can cause quite spectacular explosive events, as thewater vapour generation and thermal expansion of aggregates in the exposed surface of theconcrete can be rapid.

4.3 Fire loads in reality

Over the last years there have been a number of serious underground fire incidents in tunnels.These fires have caused extensive loss of life and severe collateral loss to the infrastructure. Asidefrom the tragic loss of life, there is also a financial effect to the local infrastructure and the loss ofpublic confidence in the safe use of tunnels [8].During a fire the fire protection system has to provide a stable structure in order to:

allow the users to safely evacuate, allow the rescue personnel to enter the scene, effectively perform their required duties and to limit damage to the tunnel, limit the effect on the surroundings caused by a collapse

250-300C generally concreteand steel start to lose strength

550C both concrete and steelhave lost 50% on their strength

20%

40%

60%

80%

100%

0%0 200 400 600 800 1000100 300 500 700 900

20%

40%

60%

80%

100%

0%0 200 400 600 800 1000100 300 500 700 900

Temperature C

%

ofInitialStrength

Concrete BS8110Concrete French DTU for HPC

Reinforcing Steel Typical

Range of concrete strengths

tested by Imperial College(Khoury et al)

Concrete BS8110Concrete French DTU for HPC

Reinforcing Steel Typical

Range of concrete strengths

tested by Imperial College(Khoury et al)Need to

keepstructuresbelow250C

Lowstre

ngthconcrete

High

strengthconcrete

Figure 6: strength reduction due to temperature


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Concrete has been used in civil works as a fire resistant material and if designed properly it canwith stand a fire for a long period. The design load in order to simulate the fire in civil works isbased on the ISO834 curve.In road tunnels the situation is complete different compared to civil works, due to the HGV (HeavyGood Vehicles) entering the tunnels. These HGV often transport combustible products, which can

cause a severe fire in case of an accident, meaning a higher fire load, higher maximumtemperatures and a faster heating rate. It is evident that concrete behaves different in these kindsof conditions.Assessment methods are constantly being developed to demonstrate the ability of materials andfire protection systems to prevent concrete spalling and steel and metal elements from heating andmelting due to rapid heating under fire exposure conditions and to mitigate both structural andeconomic consequences of fire. In the past designers have been using different kind of timetemperature curves in order to design a safe tunnel. These curves, compared to the ISO834, arereaching their maximum temperature already after 5 to 10 minutes.

Part of the European funded programs on safety in tunnels was the investigation of HRR (HeatRelease Rates) during a real tunnel fire in order to provide designers appropriate and morerealistic design curves [9]. In the frame of Swedish national and European research programs ontunnel safety, comprehensive large scale fire tests have been conducted. One of a large real scalefire was the Runehammer test in Norway in September 2003 in the abandoned road tunnel insouth-western Norway.The Swedish National Testing and Research Institute (SP) have carried out the tests incollaboration with other UPTUN partners from TNO Building and Construction Research in theNetherlands and the Norwegian Fire Research Laboratory (SINTEF/NBL). Four large-scale testswith different type of combustible loads on semi-trailer where carried out. These loads were notregistered as dangerous good or flammable liquids but consisting of normal wooden pallets orplastic cups. The outcome was that some of the design curves used until now underestimated thereal HRR during these fires. It was higher than 200 MW and the gas temperatures in the vicinity ofthe fire were registered above 1350C.As results of these tests, guidelines and directives are published and giving criteria whichdesigners can use for the fire protection of new built or existing tunnels. As an example the UPTUN

WP2 is recommending that the ISO834 can be used if there are no or only empty HGV passing inthe tunnel. The maximum HRR can be estimated on 5 50 MW. In case of HGV of course the fire

0

200

400

600

800

1000

1200

1400

0 30 60 90 120 150 180

Time (minutes)

Temperature(oC)

RW S HCM Modified Hydrocarbon HC Hydrocarbon Eurocode 1

ISO 834 RABT VIG-1

Figure 7: different tunnel fire loads in Europe


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loads can be much higher and will generate a HRR of 50 250 MW. Depending on the amount ofcombustible materials, the HC or the RWS curve is recommended.

5. Fire protection of structural concrete

Passive verses active systems

Quite often there is confusion about these terms in the tunnelling industry, amongst other things!Active fire protection systems include water sprinklers, water mists and foam deluge systems, all ofwhich are activated by early warning sensors in the event of a fire. The theory is they reduce thefire before it becomes out of control. The majority of existing tunnels worldwide rely wholly on theseactive systems to ensure tunnel fire safety. These are Boolean systems, in other words, they work,or they dont due to mechanical or electrical failure. They also may have some serious negativeeffects such as mixing with toxic fumes that are otherwise confined to the crown of the tunnel, anddrawing them down to the level of the evacuating public.Passive fire protection is designed to be installed as a shield to protect the structure from fire atany time. They are not reliant on any initiation system as with active systems, and they alwayswork. Passive systems do not put the fire out; but are the last line of defence and maintain the

stability of the tunnel structure to allow the safe escape of the public and safe access of firedepartment crews. They maintain ventilation systems that are separated from the traffic by internalconcrete structures, and also protect against catastrophic damage to third party property and lifeby preventing tunnels from collapsing.Currently in Europe, both active and passive systems employed together are seen to be necessaryfor new tunnels in the future. There are essentially three main types of passive fire protection fortunnels: spray applied mortars, prefabricated boards and PP fibre modified concrete.

5.1 Sprayed mortars

These historically have been vermiculite-cement based products applied by hand spraying with thetechnology being transferred to tunnel applications from the petrochemical industry. Vermiculitebased systems are relatively weak products (2.5MPa compressive strength) and may not offeradequate mechanical properties in light of increasing client demands for more durable solutionswhere cyclic loading resistance is required. Vermiculite systems need to be mechanically bondedto the tunnel structure with stainless steel mesh.

It is vital for sprayed systems to have adequate durability to resist both physical and chemicalattack during the normal service life of thetunnel. The new developments in fireprotection products are combining highdurability with excellent fire protection. Theseproducts are typically based on light weightconcrete technology giving a compressivestrength of 15 MPa minimum.

These products are designed for applicationwith the well know shotcrete technology andthe modern methods of robotic sprayapplication, allowing application rates ofbetween 150 and 250m2/hr depending on theprotection thickness required. The toleranceof applications is normally +/- 4mm, whichcannot be achieved by hand applicationmethods at these rates. The thickness ofspray applied thermal mortars is determinedby the size and duration of the anticipated fire.

The main disadvantage with sprayed systems is the resultant sprayed surface finish, as someclients require a high level of reflectance, particularly for highly trafficked road tunnels. Floatfinishing and over painting is possible, but labour intensive. Rail tunnel surface finish requirements

Figure 8: robotic application of fire protectionmortar


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are less onerous in general, and an as sprayed finish is acceptable, making the use of sprayedfire protection mortars particularly viable.

5.2 Pre-fabricated boards

Pre-fabricated fire protection boards offer a clear advantage for box shaped tunnels where there

are no curved tunnel walls or complex geometries e.g. cut and cover and immersed tube tunnelsas shown in Figure 8. Furthermore, the surface finish of the board systems is appealing to clients.However, they are not well suited to curved profile tunnels and are generally 1.5 to 2 times moreexpensive than sprayed systems, which can prove cost prohibitive. Apart from their high cost,vehicle collision damage is often considered a maintenance problem in road tunnels using pre-fabricated board protection systems.

5.3 Polypropylene Fibre Modified Concrete

In recent years, fibre manufacturers have promoted multi- and monofilament polypropylene fibres(32 to 18 micron diameter fibres) to contractors and design teams, detailing that the addition of 1 to3kg of fibres added to the concrete mix gives an extremely economical solution to concrete fire

protection.

From testing [10], fibre modified concrete will exhibit less spalling, and in some cases no spallingwhatsoever. One theory is that the melting of fibres at approximately 160C produces channels forescape of the steam that allows water vapour inherent in the concrete matrix to escape withoutgenerating internal pressure, thus inducing high permeability at the critical time required andthereby preventing explosive spalling. Another theory claims that micro-cracking around the fibrescontributes to steam reduction. For specific design fires, the quantity of fibres required will alteraccordingly then larger the design fire, then greater the quantity of fibres required. As anexample, for an ISO834 cellulose design fire, approximately 1kg/m3 of fibres are required,whereas for RWS hydrocarbon design fires, the quantity may increase to approximately 3kg/m3 asindicated. Concrete mixes with high fibre contents tend to be difficult to pump and place, andcareful mix designs using admixture technology to overcome these problems is required.

Although the fibres offer an anti-spalling system, they do not protect the structural concrete fromthe detrimental effects of high temperature nor do they protect any structural reinforcement at theheat exposed concrete tunnel lining. Consequently, the use of fibre modified concrete should beconsidered carefully for use in structurally reinforced concrete tunnel linings.

6. Case histories

During the last years, several existing were upgraded according to the latest requirements anddirectives. Based on a risk assessment the level of protection was determined. In some cases thecomplete tunnel had to be protected with a thermal barrier and in other cases just a small section

of the total length needed an upgrade with a thermal

barrier

6.1 Sderledtunnel, Stockholm

Due to recent legislation from the European Union,main road tunnels in excess of 300m length need tobe fire protected if a fire can cause tunnel liningcollapse, and subsequent damage of third partyproperty. One of the major Stockholm road tunnels,the Sderledstuneln lies beneath hotels and a school,and therefore required passive fire protection. Thestructure of the tunnel comprises a prestressed

reinforced concrete beam roof.The first phase of the fire protection application wasrequired d during the short tunnel closure during June

Figure 9:application on prestressedbeams


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and July 2005 to a 60m long stretch of tunnel, with a view to completing additional sections of thetunnel in September and October 2005. The program to complete the rest of the tunnel involvesapplications over a period of 5 years. The contractor preferred to apply the system by sprayedcoating, and this was required to have a design life of 100 years. The anticipated fire rating of theconcrete structures is 2 hours under a RWS fire curve. From the MEYCO Fireshield 1350 DesignGuide, a thickness of 60mm was required to both protect the concrete integrity and also the

capacity of the pre-stressed reinforcement bars of the concrete beams. The soffit sections betweenthe beams were designed with 35mm. To provide a durable solution, the MEYCO Fireshield 1350was fully bonded to the structural concrete roof of the tunnel, thereby negating the need for steelmesh. To ensure bonding, the surface of the structural concrete was hydromilled to removeapproximately 2 to 3mm of the cement pastes and reveal the aggregate structure of the concrete suitable for bonding a coating of MEYCO Fireshield 1350. Mixing of the material was carried out instandard 6m3 truck mixers that were fed with 1305kg big bags. Application of the thermal barrierwas performed using the robotic spray manipulator on a MEYCO Roadrunner Robojet

6.2 Alp Transit, Bodio section

AlpTransit Gotthard AG, a wholly owned subsidiary of the Swiss Federal Railways, is constructing a

new flat rail link[11]. At the heart of the new transalpine rail route is the Gotthard Base Tunnel(GBT). The tunnel is part of the Swiss AlpTransit project, With its planned length of around 57.1 kmand a total of 153.5 km of tunnels, shafts and passages, once finished, the Gotthard Base Tunnelwill be the longest tunnel in the world.The designers consortium of the Bodio, Faido and Sedrun Sections (total length about 38 km) ofthe Gotthard Base Tunnel is the Engineering Joint-Venture Gotthard Base Tunnel South (LombardiEngineering Limited, CH / Amberg Engineering Limited, CH / Pyry Infra Limited, CH).In 2003 the fire protection task force was founded by AlpTransit Gotthard AG with the followinggoals:

Identification of fire scenarios for freight train fire and for passenger train fire. Elaboration of a damage and risk assessment (without protection) for the different fire

scenarios. Assessment and recommendation of protective measures provided both availability

requirements are fulfilled.The cut-and-cover section of Bodio started in 2000 and was completed two years later. It consistsof two bores each of 400 m in length and one cross-passage, which is situated about 260 m fromthe southern portal. Following the investigations of the fire protection task force it was decidedthat to comply with the individual safety criterion a fire protection layer on the existing tunnel liningwas necessary on the whole length of the cut-and-cover section of Bodio. This because in theevent of a fire, it could not be excluded that damage or collapse of one bore could cause damageto the other making it impossible to evacuation users. A collapse of one of the bores could alsolead to a severe damage er even collapse of the existing train line on top of the tunnel since thistunnel section is situated in a unstable landslide.Many fire protection systems were analyzed and rated for their technical and economicalperformance. A cement based fire protection was chosen as the best solution for the cut-and-cover

section of Bodio.

The following are the requirement on the passive fire protection layer: Fire protection of the existing tunnel lining according to the RABT/ZTV standard design fire

curve (90 minutes at 1200C and the following cooling phase of 110 minutes) with respectof the following two conditions: temperature at the interface < 400C, temperature at thereinforcement


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Resistance against local perforations and against stresses induced by fixation of railwayinfrastructures.

Service life of 50 years.

Under the prescribed circumstances and requirements the application of a layer of mortar MEYCOFireshield 1350 was chosen. The minimum thickness, 31 mm, was defined on the base of the fire

protection requirements. The fire protection layer was applied on the concrete lining in both tunnelsections. Under consideration of the applying tolerance in layer thickness of 4 mm a standardthickness of 35 mm was defined (the effective layer thickness is variable between 31 mm and 39mm).To extend warranty of the high requirements in tensile bond strength of fire protection layer with theexisting lining a fully bond solution combined with stainless mesh reinforcement was chosen.

6.3 Suspended emergency escape route

The formulation of safety designs for many new or existing tunnels has led therefore to thedevelopment of a large number of innovative solutions [12]. Attention has been focused on

measures to facilitate evacuation and on the

systems installed. One of the new innovativesolutions is the suspended escape routewhich can be used in new and existingtunnels.

The design consists of an enclosed walkwaysuspended from the crown of a tunnel,providing an emergency exit large enough toprovide an easy escape route. Access to it isalong connecting stairways sited inside sidechambers or at parking areas. The walkwayis trapezoid or rectangular in shape and it isfixed to threaded bars or bolted plates. The

structure is in concrete or steel and it isprotected with materials designed to resist

high temperatures.

The first application of this innovative design has been done in Carrara. This structure provides thefollowing advantages over conventional solutions:

industrialised construction: the prefabricated components are produced under controlledconditions in a workshop and are subsequently assembled and fitted on site;

low production costs: the suspended enclosed walkway is an alternative to the costlyexcavation operations required for other solutions. Excavation is only required for the sidechambers which give access to the walkways;

rapid installation: anchor bolts are fitted in advance in the crown of the tunnel, while thestructure is already pre-assembled on the ground with threaded bars and the steelreinforcement grid for the MEYCO Fireshield 1350 mortar. The next stage consists ofraising the structure and temporarily fixing the units together and to the crown of the tunnel.The last stage consists of placing the layer of MEYCO Fireshield 1350 mortar whichprovides protection against fire.

A full scale test was therefore performed inside the S. Croce Tunnel at Carrara and performed bythe Energy Department of the Polytechnic of Turin. Numerical simulations were performedbeforehand designed to assess the environmental conditions during the test, to establish the levels

of ventilation and to conduct finite element analysis of the prefabricated segments. The fireresistance and insulation test was performed by heating the outer surface of the escape route

Figure 10: innovative design of an escape route


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operating two oil burners for 120 minutes and measuring the following: the temperature of the outer surface of the escape route at the nozzles of the burners; the vertical distribution of the temperature inside the escape route; the distribution of the temperature inside the different layers of the floor and the walls of the

escape route; the temperature of the internal walls of the escape route; temperature of the threaded bars; the rate of flow of air inside the escape route; the concentration of carbon monoxide inside the escape route; the opacity of the air inside the escape route; the increase in the length of the threaded bars; Displacement of the joints between the prefabricated segments.

7. References

[1] CORRADI, M; KHURANA, R; MAGAROTTO, R; TORRESAN, I; : paper Zero energy systeman innovative approach for rationalized precast concrete

[2] SHUTTLEWORTH, P. (2002). Technical Paper Fire protection of concrete tunnel linings.Written communication based on Rail Link Engineering tests for Channel Tunnel rail Link, UK.[3] BREUNESE, A, Efectis The Netherlands: Presentation Fire Protection workshop, MEYCO

Global Underground Construction, 2009[4] ITA (2004). Guidelines For Structural Fire Resistance For Road Tunnels. Working Group 6

Report. Published by the International Tunnelling Association, 2004.[5] KHOURY, G.A. (2003). EU Tunnel Fire Safety Action. Tunnels and Tunnelling International.

February 2005. pp 20-23.[6] KHOURY, G.A. (2005). EU Tunnel Safety Update. Tunnels and Tunnelling International.

February 2005. pp 41-43.[7] KHOURY, G.A. (2005). Personal written communications on SafeT findings and concrete

strength change on elevated temperatures research work undertaken by Imperial College,London.

[8] MUNICH Re. (2003). Risk management for Tunnels. Published by the Munich Re Group,Munich, Germany. Order No. 302-03083.

[9] INGASON H.(2006) Paper Design fires in Tunnels, Safe & reliable tunnels Lausanne 2006,SP Swedish National Testing and Research Institute

[10] ADFIL UK. Ignis Passive Fire Protection System. Product brochure for monofilamentpolypropylene fibres. Published by ADFIL UK Ltd.

[11] VERANI C, FERRARI A: Fire protection for new and existing underground structures, Tunnelmagazine 7/2009

[12] FOCARACCI, A Prometeoengineering.it srl, (2009): Safety in tunnels: innovation andtradition

wtc 2011 paper fire protection in tunnels

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