Comments (0)

|

Comments This Article

Gotthard Base Tunnel (GBT)

World’s Longest Tunnel in Alps

Introduction

 

Figure 1: GBT Path between Zurich and Lugano

The world’s toughest and hardest engineering marvel of our era is taking shape in the wombs of treacherous mountain ranges of Alps. Tipped to be the world’s longest underground rail tunnel, the GBT, as it is popularly known, slowly inching towards completion through the formidable obstacles of Alpine mountains. GBT being one of the biggest infrastructure projects in Europe ever, construction involves two base tunnel projects – Lotschberg and Gotthard. The 36 kilometre Lotschberg Base Tunnel was inaugurated in 2007, but the system will only be fully operational with the completion of the key project – the 57 kilometre long Gotthard base tunnel that is known as the Alp Transit Gotthard (ATG) project. Figure 1 shows the GBT path between Zurich and Lugano.

For centuries, the Alps have served as a natural trade barrier between northern and southern Europe. The amount of freight crossing the Alps in heavy goods vehicles has risen sharply over the last two decades. In 1990 an estimated 40million tonnes went by road, in 2001 that had risen to 90m tonnes, with further big increases expected by 2020. Subsequently, Switzerland’s New Rail Link through the Alps (NRLA) was rested with the responsibility of providing a faster and more reliable rail link between northern and southern Europe enabling much of the freight traffic to be shifted from road to rail. This necessitated two NRLA lines: the Lötschberg axis in the west, and the Gotthard axis in central Switzerland. Preliminary work for the Gotthard Base Tunnel started in 1996, with excavation of access tunnels and shafts.

To save construction time, the tunnel was divided into five lots, two of which are situated near the portals at Erstfeld in the north and Bodio in the south. The three intermediate lots at Amsteg, Sedrun and Faido use access tunnels and shafts to reach the base tunnel levels that were completed 2001. Construction started on the running tunnels and multifunctional stations in 2002 by consortium TAT – a joint venture of leading companies from Switzerland, Germany, Italy and Austria. The running tunnels are excavated by two giant tunnel boring machines (TBMs), while the multifunctional stations are excavated by traditional drill and blast methods. The excavated material is converted into concrete aggregates on site to produce sprayed and insitu concrete for the inner lining of the tunnel system.

(yellow: major tunnels, red: existing main tracks, numbers: year of completion)

The complete tunnel system consists of 153.3 km of access tunnels, shafts, railway tunnels, connecting galleries and auxiliary structures. Excavation of the main system started in 2002. More than 108 km, or more than 70% of the full 153.3 km of tunnel system, had been completed by the end of March 2008. The entire operation of excavation adopts both methods of excavation judiciously- The conventional tunnelling method as well as TBM method. With an estimated total rock excavation of about 24 million tons, TBMs do about 60% share.

Much of the tunnel will have a very high overburden: more than 1,000 m overburden over approximately 30 km of the tunnel, more than 1,500 m over 20 km, and more than 2,000 m over approx. 5 km. The maximum overburden is about 2,400 m. Figure 2 shows the overburden profile of GBT link. Kalman Kovari, an emeritus professor of tunnelling at the Federal Institute of Technology Zurich and consultant to the project, says that “tunnelling is not quite as mystical as its reputation. It is simply an engineering activity using natural formations as its material”.

Figure 2: The overburden profile of GBT link.

An another important feature of the project is the fact that the entire railway line will stay at the same altitude of 500 metres (1,650ft) above sea level. This will allow trains using the line to reach speeds of 240km/h (149mph), reducing the travel time between Zurich and Milan from today's four hours to just two-and-a-half. That would make the journey faster than flying. The magnitude of the work that is happening in this restricted area is mind boggling. 2000 skilled and specially trained workers working round the clock and 365 days a year,

 The Configuration

Figure 3: An overview of GBT.

The Gotthard Base Tunnel consists of two parallel single-track tubes with an excavation diameter varying from 8.8 to 9.5 m and linked by cross-passages approximately every 312 m. Two multifunction stations (MFS) are located in the Sedrun and Faido sections, one-third and two-thirds along the length of the tunnel respectively. These will be used for the diversion of trains to the other tube via crossovers, to house technical infrastructure and equipment, and as emergency stopping stations for the evacuation of passengers.  Figure 3 shows an overview of GBT.

The logistics of a project of this size is simply awesome. The giant twin TBMs are 10 metres in length and have cutting faces of 9.5 metres. They are also set up to carry primary support measures such as rock bolts, wire mesh and shotcrete. At peak performance, a TBM can take make 38 metres a day. Waste from the TBMs is excavated by muck trains made up of two 35 tonne locomotives pulling 10 cars with a loading capacity of 24 square metres. The material is hauled out to a multi-car rotary tip near a recycling plant.

Massive amounts of concrete are produced for lining the tunnel sections. For the 16.5 kilometre Bodio section in 2001, for instance, a joint venture between Holcim and Sika produced one million cubic meters of in-situ concrete for the inner lining, and 250,000 square metres of sprayed concrete (shotcrete) for primary rock support and inner lining of caverns, crossovers, and rescue and ventilation tunnels. Concrete is moved from the batching plant by trains made up of four to five concrete mixer cars carrying 12 square metres of concrete and pulled by a 35 tonne locomotive. The batching plant has a capacity of 120 square metres an hour, and has already produced almost a million square metres of concrete. The maximum output for one day was 1200 cubic metres.

“For such a huge project you have to construct from different sites because if you start at one portal and then on the other end, you need 20 or more years for the construction of the entire system,” Heinz Ehrbar, chief construction officer with the contractor AlpTransit, told swissinfo.ch.

Excavation Methods

Figure- Gotthard base tunnel, volume of excavated material.

The excavation for the tunnelling involved both methods namely, the conventional and the TBM. The principles of which are briefly described below:

Conventional Tunnelling

Conventional tunnelling is carried out in a cyclical process of steps, each comprising excavation followed by the application of relevant primary support, both of which depend on existing ground conditions and ground behaviour. An experienced team of tunnel workers (miners), assisted by standard and/or special plant and equipment, executes each individual cycle of tunnel construction.

The conventional tunnelling method using mainly standard equipment, and allowing access to the tunnel excavation face at almost any time, is very flexible in situations or areas that require a change in the structural analysis or design, and as a result also require changes in the supporting measures. A standard set of equipment for conventional tunnelling may consist of the following items:

• Drilling jumbo to drill holes for blasting, rock bolting, water and pressure release, grouting etc.
• Road header or excavator in cases where blasting is not possible or not economic.
• Lifting platform allowing the miners to reach each part of the tunnel crown and tunnel face.
• Lifting equipment for steel sets.
• Loader or excavator for loading excavated rock onto dump trucks.
• Dump trucks for hauling excavated rock.
• Set of shotcrete manipulators for application of wet or dry shotcrete.

Conventional tunnelling in conjunction with the wide variety of auxiliary construction methods allow experienced project managers to make the most appropriate choice to achieve safe and economic tunnel construction even in situations with changing or unforeseen rock conditions. It allows response in both directions – depending on the rock –changing towards the less or more favourable side. This flexibility makes conventional tunnelling the most advantageous tunnelling method in many projects, which can be located at a shallow depth or under a high overburden, in stable or loading ground, under genuine rock pressure, below the phreatic surface or in dry conditions. Therefore conventional tunnelling is the best method for projects with highly variable rock conditions or variable shapes. Conventional tunnelling allows;

• Great variability of the shapes,
• Great variability in the choice of excavation methods according to the rock conditions,
• Great variability in the choice of excavation sequences according to the rock conditions,
• Optimisation of the primary support using the observational method,
• Great variability in the choice of auxiliary construction methods according to the rock conditions.

Conventional tunnelling is especially appropriate for;

• Difficult rock with highly variable rock conditions,
• Projects with highly variable shapes of cross section,
• Projects with a higher risk of water inflow under high pressure,
• Projects with difficult access,
• Short tunnels.

Tunnelling using TBM

Figure -TBM Mechanism

Tunnelling by TBM is used for the excavation of underground openings of normally circular shape under many types of geological condition, varying from hard rock to very soft sedimentary layers. Procedures commonly used for tunnelling by TBM are;

• Excavation with a rotating cutter wheel in a cyclical or continuous drilling process
• Mucking with a mechanical discharging devise
• Placement of primary ground support elements such as
• Concrete segments
• Soil or rock bolts
• Steel ribs
• Meshes
• Shotcrete

There are two types of tunnel boring machines (TBM) are deployed depending upon the geological and hydro-geological conditions of soil, rock and water table in the tunneling site. They are the Slurry TBM and Earth Pressure Balanced (EPB) TBM.

Earth Pressure Balanced (EPB) TBM provides constant support to the tunnel face by balancing the inside earth and water pressure against the pushing pressure of the TBM. In case of Slurry TBM, constant support is provided to the face of the tunnel by balancing earth and water pressure in the in-situ soil with pressurized slurry (bentonite). Both in the (EPB) TBM and in the Slurry TBM, the excavated soil and rock is collected under pressure in the cutter-head container and it is then extracted by conveyor belt to the rear of the TBM, where it drops into carts that transports it out of the tunnel. The rate of advance of the TBM and the rate of extraction of the excavated material by the conveyor belt regulates the pressure in the cutter-head container.

In the case of the slurry TBM, the cutter-head (face of the TBM shield) slowly rotates and grinds away the rock and soil in front of it.  Slurry (Bentonite) is pumped through the TBM shield to make it easy to carry the soil-rock muck. To move deeper into the tunnel, the TBM is constantly pushed forward by the pressure exerted by hydraulic jacks at the rear of the TBM pushing against the RCC liner segments already in place. As the TBM excavates the tunnel area, the TBM casts the tunnel walls with precast bolted and gasketed RCC liner segments.

To avert the TBM from tilting due to the rotation of the cutter-head, trailing support systems are installed outside the TBM body. Muck is collected through the holes in the TBM cutter-head and carried by conveyor belt to the rear of the TBM, where it drops into carts that transport it out of the tunnel into the slurry recycling plant, where the muck and water is segregated. The water and slurry is recycled back into the TBM.

(EPB)TBM and slurry TBM are operated by civil engineers specializing in systems who use sophisticated computers and state-of-the-art instruments. Inside the tunnel path, the geographical position of the TBM and the geological conditions like water table, soil and rock components ahead of the TBM is detected by the use of GPS, sensors, laser instruments, guidance systems and virtual CAT scanners.

Tunnelling by TBM usually allows high advance rates, which, in similar ground conditions, are significantly higher than (more than double) the rates attained by conventional tunnelling. Tunnelling by TBM is generally appropriate for;

• Projects with constant shapes of cross section
• Long tunnels
• Projects with good accessibility

Geological Conditions

Figure 4-Geology of the Gotthard Base Tunnel.

From north to south, the 57 km long Gotthard Base Tunnel passes through mostly crystalline rock, the massifs which are broken by narrow sedimentary zones, the tectonic zones. The 3 crystalline rock sections are the Aar-massif in the north, the Gotthard massif in the middle and the Pennine gneiss zone in the south-Figure 4. These zones are unlikely to cause any major technical difficulties during construction and they are quite favourable for tunnelling. These units consist mainly of very strong igneous and metamorphic rock with high strength. More than 90% of the total tunnel length consists of this type of rock. The main danger is the risk of rock burst caused by the high overburden, the instability of rock wedges and water inflow.

Major sections of the tunnel will have a very high overburden: more than 1,000 m for roughly 30 km, more than 1,500 m over 20 km and it can even be more than 2,000 m for approx. 5 km, the maximum is about 2,300 m. This has been taken into consideration in deciding the heading concept and rock support design.

 

Figure 5-Investigations in the Sedrun section.

The most difficult section facing the new tunnel is the so called (old crystalline) Tavetsch intermediate sub-massif in the Sedrun section. Located between the Aar-massif and the Gotthard-massif, it is one of

the about 90 different isolated short fault zones along the 57 km. It consists of a steeply-inclined, sandwich-like sequence of soft and hard rock. Exploratory drilling in the early nineties indicated extremely difficult rock conditions for about 1,100 m of the tunnel-Figure 5. As well as compact gneiss, there are also intensively overlapping strata of schistose rock and phyllite.

In the Faido section the Piora syncline has been deeply investigated in the second part of the nineties.

The initial planning phases concentrated on cutting through the different fractured zones at their narrowest points wherever possible. The high mountain overburden of up to 2,300 m means that operating temperatures in the tunnel can reach 35-40°C. In order to maintain the required air conditions in the different working areas, a continuous cooling system is required.

Environmental considerations

The Swiss population is in general very sensible for environmental problems and the Swiss government did and does set high priority on the preservation of the territory and of the water resources. Several federal laws prescript measures to protect persons and the nature from contamination, pollution, noise and different kinds of waste. An important recycling quote has to be attempted. To respect all these incisive dispositions, different concepts and technical solutions have been adopted in this project in order to reduce as far as possible temporary and permanent effects caused by the construction works and by the final deposit of the muck.

The volume of the excavation of the complete Gotthard base tunnel (including galleries and multifunctional stations) is estimated in about 13.3 millions of cubic meters; with the entire produced volume of muck it would be possible to build five new pyramids with the same size of those of Cheops (see Fig. 17). On all construction sites material processing plants have been realized in order to recycle the muck and to produce concrete aggregates. Depending from the petrography and the properties of the excavated material, according to the predicted geology, about 28% of entire muck will be processed; the expected recycling rate is around 85% (concrete aggregate production about 22% of entire muck). A part of it is used as filling material and the rest is transported to final deposits or to an inert landfill (see Fig. 18).

 

Figure- Gotthard base tunnel, recycling of excavated material.

The contamination of the muck – cause of loss of oil from the machines (especially the TMBs), waste products from the use of explosives, chemicals and heavy metals from rebounded shotcrete – not ever permit to store this material in a “conventional” inert landfill. The requirements for “non contaminated” muck are very high and at the present time about 1% of the excavated material of the section Bodio has been transported to a special reactor landfill. This is related to intensive costs, caused by the extremely high level of the deposit and treatment prices. To reduce noise and pollution, muck is transported with conveyor belt systems above ground and it is sprayed with water to avoid dust production.

Wastewater from the tunnel and from several technical installations outside the tunnel is treated to reduce the acidity (pH), to neutralise chemicals, to separate oils and particles in suspension. After the treatment, if necessary, the temperature of the cleaned water has to be reduced prior to the introduction in a river or before being recycled for industrial use or as liquid for the cooling system in the tunnel (see Fig. 19, treatment of maximum 200 l/s, recycling of about 5÷10 l/s). The mud cake resulting from the treatment of wastewater is pressed to reduce water content and is handled with the same criteria for the muck. In general the quality of the cake is “contaminated”, especially because of the concentration of oils.

To reduce the impact of noise from the construction sites on the nearby living populations the required standard of some installations, like tunnel train wagons, have been set very high. Concrete production plant, material processing plant and conveyors belt systems have been encapsulated (see Fig. 19). Temporary dams and absorbent walls have been extra erected to avoid the propagation of very noisily activities.

General Infrastructure

Following completion of the shell structure, and before installation of the railway systems, the base tunnels are now being equipped with mechanical and electromechanical systems. The technical infrastructure systems comprise ventilation, water supply and drainage systems, ventilation and air-conditioning systems for auxiliary structures and buildings, cranes, doors, technical floors and metal structures, as well as electrical and fire-protection installations. Most of the systems will be installed in the cross passages and the two multifunction stations of the Gotthard Base Tunnel, some also in the tubes and portal areas of the tunnel.

Cross Passages

Through installation of the respective technical systems, the 176 cross galleries in the Gotthard Base Tunnel and the 46 cross galleries of the Ceneri Base Tunnel take on various different functions: they form protected rooms to accommodate cabinets containing railway infrastructure systems. So that the temperature does not rise above 35 °C and thereby impair the high availability and long life of the systems, the cross passages are equipped with a ventilation system. In the event of an incident, the cross passages serve as evacuation routes into the unaffected tube. For this reason, they are closed off with evacuation and fire-protection doors.

Fresh Air

The operational ventilation prevents an unfavourable climate in the tunnel system and provides the necessary air conditions for personnel involved in maintenance work. In the event of a fire in the tunnel, it can suck fumes out and blow fresh air in. An optimal operating climate in the tunnel is important for the high availability and long life of the technical systems. In summer, the temperature will be around 36-37 °C, in winter, around 35 °C. The tunnel temperature is determined, among other things, by the rock temperature, the temperature of the train when it enters the tunnel, the heat emitted by the technical installations, and the ground water temperature. In the tunnel entrance areas, the relative humidity of the air can be over 70%. With increasing air temperature in the direction of travel, the relative humidity decreases until at the exit portal it is only between 20 and 40%.

Removal of ground water and soiled water

In the Gotthard Base Tunnel, ground water and tunnel water flow out of the tunnel in special pipes. Before it flows out, the tunnel water is examined, processed to the extent necessary, and returned to the natural environment. In the event of soiled water collecting in the area of the trackbed, at 100-metre intervals it is collected in a shaft and drained into a separate pipeline. The soiled water runs into a collection basin outside the tunnel, where it is analysed.  In the Ceneri Base Tunnel, the ground water and soiled water are not drained separately. The much smaller volume of ground water allows a mixed drainage system.

Multifunction Stations

In both multifunction stations, trains can cross over from one tube into the other. These tunnel crossovers are equipped with special doors which under operating conditions are normally closed. Numerous technical rooms in auxiliary buildings, such as the railway infrastructure systems rooms, must be air conditioned. For this reason, they are equipped with building control systems for cooling and ventilation. Under operating conditions, Shaft I at Sedrun serves not only as a fresh-air duct to the Gotthard Base Tunnel. It also houses various cables for the railway systems and a water pipeline for the multifunction station.

Safety Systems

As duly described by Davide Fabbri, Chief designer Engineering joint-venture Gotthard Base Tunnel South in his paper- The Gotthard Base Tunnel: Fire / Life Safety System, presented during the 6th annual Tunnelling Conference Sydney, 2004-A high safety level is a very important premise for the operation of a railway tunnel and as well an economic exigency. In order to plan and realise a safe operating base tunnel, a safety concept serves as a rail-internal instrument for continuous planning and optimisation of safety measures and as a transparent basis for the control by the competent authorities. The analyses in the Gotthard Base Tunnel safety concept demonstrate, that with simple but very effective measures, a very high safety level can be reached, corresponding to the demanded safety requirements.

The tunnel system (see Fig. 2) mainly consists of two single track tunnels with two train-crossover sections in the so called multifunctional stations. Along the tunnel, cross passages are located every 310÷325 m approximately; the horizontal distance between the tube axes is varying between 40 and 70 m. In front of the tunnel portals turn-out tracks are arranged.

For tunnel safety planning, in first priority preventive measures have been designated and in second priority curative measures have been defined in addition. This principle paid off during decades in railway technique. Should an incident happen in spite of these measures, particular measures facilitating the self- and external rescue will be applied.

In general every failure of the safety system has to be prevented, otherwise the personnel on the spot (train crew, engine driver) has to deal with it (radio contact to the control centre). If unsuccessful, the train has to leave the tunnel or stop at an emergency stop station with highest priority. Assistance from

the outside can be expected – depending on the exact position of the train in the tunnel – after 30 minutes at the earliest (e.g. train at emergency stop station).

In the tunnel control centre well-trained Traffic-Controllers survey the train running and the technical infrastructure. The Swiss Federal railways develop an early warning system to detect irregularities in the operation in real time. In case of an incident the Traffic-Controllers activate defined and rehearsed procedures using check lists. Always the purpose is to manage the situation quickly, preventing an escalation. It is also important to ensure the operating flow and to achieve a stable operating situation.

 Fire on board

 In case of a fire on board of a (passenger) train, the procedure of the safety concept depends on the position of the train in the tunnel. Three cases have to be taken into account:

1. The train is running in the last section of the tunnel (after the second multifunctional station): the train has to reach the portal and will stop in the open air. Passengers are able to leave the train.

2. The train is running in the first or in a intermediate section of the tunnel: the train has to reach the next multifunctional station and stops there for the evacuation of passengers (see Fig. 3). The passengers reach the “sheltered area” of the emergency stop station within 3 to 5 minutes. Prior to the arrival of the train, after the fire-alarm, the lights of the emergency station will be turned on, the sliding-doors of the escape ways will be automatically opened and the ventilation system starts the extraction of smoky exhaust air from the traffic tube trough the middle of the seven fire dampers (only after exact location of the fire it will be possible to open the nearest fire damper).

After evacuation from the train – without using stairways or elevators – passengers will wait at the emergency stop station of the opposite tube for a rescue exclusively by train (multifunctional station Sedrun: no evacuation through the shafts; multifunctional station Faido: no evacuation through the access tunnel).

The emergency stop stations (sheltered areas) as well as the lateral and connecting galleries are furnished with fresh air independent of the traffic tunnel system, they are kept smoke-free through overpressure. An evacuation train conducts the passengers outside the tunnel. And this leads to another principle: the rescue from the outside is rail-bound. The evacuation train is either a train emptied in front of the tunnel or a train already in the tunnel.

Fire-fighting and rescue trains come in action from the south-end as well as from the north-end of the tunnel. The rail-bound rescue is proven and trained for years at the Swiss Federal Railways (Simplon Tunnel 19 km, Gotthard Tunnel 15 km). In order to shorten the time period until the forces are ready, a close co-operation with local intervention forces (fire brigade, ambulance and police) is of great importance. This represents an extraordinary challenge for the upcoming years.

3. A fire event occurs and the train is not able to reach the next multifunctional station or to exit the tunnel. In this case the train will stop at any position in the tunnel and the evacuation occurs. On a 1 m-wide side walk escaping passengers will be able to reach and to enter the next cross passage and reach the safe tube (see Fig. 4). In the opposite tube the speed of the trains running is reduced immediately after alert, minimizing the run over risk for escaping people. In this case the process of the external rescue proceeds in the same way as if the train stopped in an emergency stop station. In any case the train crew has to act quickly and resolutely. Early and clear instructions help to prevent panic situations.

Fire-resistant doors (90 minutes resistance with AlpTransit temperature-time-diagram) will provide fire-protection of the escape way and of the technical equipment inside the cross passages. The ventilation system will assure overpressure conditions in the safe tube to avoid the propagation of smoke from the burning one.

Ventilation System

In the system of the Gotthard Base Tunnel, emergency stations are located in the multifunctional stations, where burning trains will stop in case of fire. To permit an efficient and safe evacuation of the passengers, it is required to extract exhausted air (smoke) near to the fire and to supply fresh air with overpressure in the escape ways and in the opposite tube (see Fig. 5). Main fans (redundant, 2 x 2.6 MW for extraction and 2 x 0.5 MW for fresh air) will be installed in the ventilation plant located near the portal of the intermediate access of Faido as well as in the ventilation plant in the cavern on shaft top in Sedrun. The amount of air blown in and exhausted will be about 200 m3/s and 250 m3/s respectively. In each emergency station seven fire dampers, located on the top of the lining, and six emergency sliding doors will complete the ventilation system.

Mile Stone

A milestone has been reached in construction of the Gotthard Base Tunnel with the start of pilot operations in the west tube. A train that has travelled under the Alps along the 13km-long pilot section from Bodio to Faido at a speed of 160km/hour, running of the test train took place 900 days ahead of the inauguration of the world's longest railway tunnel in June 2016.

"The six months of pilot operation are an important prerequisite to enable us to hand over the tunnel to the government and Swiss Federal Railways ready for operation at the beginning of June 2016," said Renzo Simoni, chief executive officer of AlpTransit Gotthard.

The purpose of pilot operation is to obtain preliminary confirmation that the entire tunnel system meets the specified requirements. Tests will be conducted of the interplay between the various processes, systems and equipment such as the track, overhead conductor, power supply, tunnel infrastructure, train control and safety, as well as operational communications.

Between now and June 2014, trains will travel over the pilot section at speeds reaching a maximum of 220 km/h. Construction of the new rail link through the Alps involves the creation of base tunnels under the Gotthard and Ceneri. The new railway link crosses the Alps with minimal gradients and wide curves to allow efficient rail transport of goods as well as shorter journey times in national and international passenger traffic. Completion of the Ceneri Base Tunnel is due at the end of 2019.

Holcim’s scope

For the Bodio and Faido sections of the tunnel Holcim provided an integrated ready-mix concrete (RMX) solution fully tailored to the project. Holcim has set up a unique plant specially designed by its engineering experts. Its rail logistics enables the transport of the cement to the project site in a sustainable way. Holcim designed the high-tech RMX and supplied the total volume of 1.3 million cum for these two sections. 100% of the required aggregates for concrete come from the recycling of the excavated material.

A consortium in which Holcim is involved was awarded the material management work package for Bodio, Faido and Amsteg, which includes the processing of excavated material into aggregates for concrete and the reutilization of the rest for other purposes. Furthermore, Holcim is also responsible for providing the cement required for the Sedrun section.

BASF Role

As per the Press Release by BASF October 07, 2010- BASF supplied concrete admixtures, concrete spraying machines and fire protection mortar for two of five construction sections, around 20 km of the total tunnel length (57 km). Between Erstfeld and Sedrun, concrete admixtures supplied by BASF have been used for construction of the tunnel lining of the two parallel tunnel tubes and the cross passages that connect the tubes every 300 meters.

“When used for underground work, concrete must meet the most contradictory requirements: when being transported over several kilometers into the mountain it is essential that the concrete does not harden and that it continues to be workable for hours. As far as the Gotthard Tunnel is concerned, this is one of the greatest challenges. On the other hand, the concrete must solidify in a flash as soon as it is applied to the tunnel wall,” says André Germann, Manager of MEYCO Underground Construction for Germany, Austria, Switzerland and Eastern Europe.

This is made possible only by using the correct combination of concrete admixtures: various superplasticizers sold under the GLENIUM® brand make concrete especially free flowing. The MEYCO® SA 160 accelerator for sprayed concrete on the other hand ensures that concrete, once applied to the tunnel wall, solidifies in seconds.

In order to meet the special challenges concerning the processability of concrete in the Gotthard Base Tunnel, BASF has developed the DELVO® Crete Stabilizer 10. This admixture slows down cement hydration and ensures an open time of four to six hours. Combined with the GLENIUM® superplasticizers, the concrete can be used perfectly well even when being transported over long distances and exposed to the high temperatures in the interior of the mountain. In the Gotthard Base Tunnel, this system combining superplasticizers with retarding agents has been used for initial securing measures after excavation as well as during the concreting of the inner shell.

In addition, BASF’s MEYCO® machines MEYCO® Potenza and MEYCO® Oruga concrete spraying units were used in the two construction sections between Erstfeld and Sedrun, in the northern part of the tunnel, for construction of the primary tunnel lining (reinforced sprayed concrete) just after excavation of individual tunnel sections by the tunnel boring machine (TBM). These special machines have been developed to cope with the difficult conditions during tunnel construction. By means of MEYCO® Potenza and MEYCO® Oruga spraying units concrete was applied quickly onto the excavation  surface immediately after removal of excavation material, enabling rapid building of excavation support and safety of working crew.

Further, the MEYCO® Fireshield 1350 fire protection mortar manufactured by BASF protects the concrete tunnel lining of the Bodio tunnel section near the southern entrance of the tunnel against excessive heat in the case of fire. Application of this special fire protection mortar was required, since temperatures exceeding around 300 degree Celsius lead to concrete crumbling, and when concrete is exposed to temperatures above 1,000 degree Celsius it loses its load-bearing capacity altogether and the tunnel may collapse.

“Being covered with a layer of fire protection mortar the tunnel walls withstand temperatures of up to 1,400 degree Celsius for a minimum of 90 minutes. This way we gain some precious time for firefighting,” says Frank Clement, BASF expert for underground fire protection solutions.

BASF’s MEYCO® Suprema spraying unit and the MEYCO nozzle system, which is specifically adapted to fire protection mortar, were used to apply a layer of a specified thickness onto the inner concrete lining of the tunnel.

Risk Management

Figure: Risk classification and management strategy¹

Geological risk has remained to be the most vital risk factor in GBT execution. Some of the key questions like what could hinder, or even prevent, accomplishment of the goal and what could further, or assist, accomplishment of the goal have remained unchanged since inception. In other words, what are the risks that we must be able to master and what are the opportunities that we must exploit underlie the overall process of risk management, comprising risk identification, risk evaluation and classification, application of the action strategy, planning and monitoring of contingency measures.

Risk identification is concerned with promptly recognising and describing the risks and opportunities. At AlpTransit Gotthard Ltd (ATG), when elaborating and periodically updating the risk lists, in addition to employees of ATG, the project engineers and geologists, construction managers, external specialists and, depending on the phase of the project, also the contractors of the major tunnel lots are involved. This has ensured that the greatest possible amount of expert knowledge is used. In the next step, the risks are evaluated and classified according to their relevance. The evaluation is based on a weighted score for each risk or opportunity. The weighted score is the product of the score for the expected extent of the damage or benefit and the score for the probability of its occurrence.

Following a systematic methodology involving following steps, the risk management strategy at GBT was evolved based on continuous learning and case studies:

• Identify all possible hazards
• Evaluate risks by severity of damage and probability of occurrence
• Develop mitigating measures
• Evolve a safety system
• Registering all risks experienced and learning from failures.

Status as reported in April, 2014⁹

• Over ground section north- SBB Maintenance has installed a protective point. Track 5 has been extended from the Stille Reuss bridge to the Riedstrasse underpass, as has also the preliminary ballasting of Track 6. Further points have been installed in front of the east portal north. Construction of the drainage system at Erstfeld is in progress.

• Gotthard Base Tunnel overall- On March 15, 2014, the first joint exercise with the fire services from Erstfeld/Amsteg/Silenen and Biasca took place. Planning work for connection of the communications network with optical-fibre cables to the SBB network in Altdorf is in progress.

• Erstfeld-Faido east and west- In the Sedrun-Faido section of the west single-track tube, at the end of March 2014 the ballastless track had been laid as far as Km 239.110.  In the longitudinal and lateral caverns of the MFS at Sedrun, the 16.7 Hz cables for the tractive power supply have been installed.

• In the side-tunnel Sedrun North and in the emergency-stop station north-east, the cable trays are being installed. In the area of the emergency-stop station Sedrun North, installation of the evacuation-route components has begun.

• The cross-passages between Sedrun and Faido are being successively fitted out with the power-supply components (electrical enclosures, transformers). Connection of the medium-voltage systems has begun.

• Between MFS Sedrun and MFS Faido, the antenna cables for the Polycom wireless security network and the communications network are being installed.

• Also in the same section, various other work activities such as installation of the ring-earth, tensioning of the catenary supports, and installation of the amplification conductors are in progress.

• In the railway systems building at Erstfeld and the MFS at Sedrun, installation of the electrical enclosures for the communications systems is in progress.

• In the access adit at Sedrun, the supply line for the trickle water-flow is now being installed.

• Faido-Bodio east and west- On March 11 and 12, 2014, in the Faido-Bodio West section, the second phase of the dynamic subsidence measurements took place. These measurement runs were conducted at speeds above 160 km/h to fulfil the requirements of FOT. In the Faido-Bodio East section, the tunnel supports are being installed.

Author- Sahania Swenson, Techno-Journalist, Milano

References:

1. Risk Management for the World's Longest Railway Tunnel: Lessons Learnt by Dr. sc. techn. Rupert H. Lieb, Head of Construction Management, AlpTransit Gotthard Ltd, Switzerland and Heinz Ehrbar, Chief Construction Officer, Gotthard Base Tunnel, AlpTransit Gotthard Ltd, Switzerland.

2. The GBT-Project Overview- by Davide Fabbri, Chief designer, Engineering joint-venture Gotthard Base Tunnel South

3. Under the Alps-Presentation by Team Alpha

4. Tunnelling in Rocks-ZAHO Zian, Professor of Rock Mechanics and Tunnelling, EPFL, Switzerland

5. GBT-Presentation by Group Ryon

6. Ventilation with Safety, World Tunnelling, April 2000, Dr Fathi Tarada, HBI Haerter Ltd., Switzerland

7. Gotthard Base Tunnel, Switzerland; Experiences With Different Tunnelling Methods, Heinz Ehrbar1

8. The Gotthard Base Tunnel: Fire / Life Safety System; by Davide Fabbri, Chief designer, Engineering joint-venture Gotthard Base Tunnel South

9. http://www.alptransit.ch/en/status-of-the-work/railway-infrastructure/gotthard-base-tunnel.html

10. Control Surveys in GBT-R.Stengele, I.Stahlin

GBT FEATURES

• Route over Gotthard Pass is one of the most important passages through the Alps.
• Largest engineering project since the Panama Canal.
• Two tunnels, each 57 km long, 9.5m in diameter.
• Max overburden – 2.5 km.
• 27 million metric tons of excavated rock.
• 200-250 trains/day.
• 40 meters/day of drilling.
• Satellite mapping.
• Initial Gotthard cost: $7.2 billion USD
• Final Gotthard cost: $10.1 billion USD
• 60 year payback period- 88% said “money well spent”
• 2000 workers, working 24hr per day.
• TBM is of about 450 meters long.
• Total of 90 geologic problem zones.
• Two parallel tunnels, each fitting one rail track.
• Two “cross-over” sections for allowing trains to switch tracks in the middle of the tunnel.
• Three access tunnels (Amsteg, Sedrun, Faido) for emergency and service purposes.
• Multiple interconnections for foot travel between the two separate tunnels.
• Tunnels were connected every 300 meters.
• TBMs weighed 3000 tons each.