ORAL PAPER PROCEEDINGS

Transcription

1 ITA - AITES WORLD TUNNEL CONGRESS April 2018 Dubai International Convention & Exhibition Centre, UAE ORAL PAPER PROCEEDINGS

2 Ultra-long subsea tunnel under the Gulf of Finland ABSTRACT Klaus Wachter 1, MSc, Felix Amberg 2, MSc, and Malla Paajanen 3, MSc, LicSc 1 Amberg Engineering Ltd, Switzerland, kwachter@amberg.ch 2 Amberg Group Ltd, Switzerland, famberg@amberg.ch 3 Helsinki-Uusimaa Regional Council, Finland, malla.paajanen@uudenmaanliitto.fi TheLINK consortium, consisting of Amberg Engineering, Sweco Environmental Oy and WSP Finland Oy, was commissioned by Helsinki-Uusimaa Regional Council as Lead Partner, the Finnish Transport Agency and other project partners to develop a technical concept and economic assessment at feasibility study level for a Helsinki-Tallinn fixed link (the FinEst Link project). Amberg Engineering is responsible for the overall project management and the design and the safety concept of the over 100 km long railway tunnel underneath the Gulf of Finland. WSP is working on the geological-geotechnical assessment, the alignment under the city of Helsinki and the train operation concept including passengers, stations, workshops and freight roll-on/roll-of stations. Sweco covers topics such as the maintenance concept, the strategic environmental assessment as well as the economic assessment. The FinEst Link consists of two single-track tubes, connecting cross passages and a service tunnel which lies in-between the two running tunnels and is interconnected with existing or planned future railway lines and stations both in Finland and Estonia. For logistic reasons, risk mitigation and reduced construction time, intermediate accesses are required. Therefore, two artificial islands will be constructed in the middle of the sea providing access to the tunnel drives and offering space for material storage, installations as well as harbour facilities. The tunnel will be situated mainly in crystalline basement and will be excavated by TBM and segmental lining. At its lowest point, the tunnel will run at a depth of more than 200 m below sea level. This paper gives an overview of the FinEst Link project, its strategy and encountered challenges regarding the technical complexity and specific design requirements of this ultra-long subsea tunnel. Key words: Subsea tunnel, TBM drive, Artificial islands, Cross-border project 1. INTRODUCTION The fall of the Iron Curtain in 1991 launched a new era in the economic and social interaction between the capitals of Finland and Estonia Helsinki and Tallinn. Since then the cross-border region has developed remarkably and the annual passenger volume has grown from 2 million (in 1993) to almost 9 million (2017) passengers. Helsinki is an urban node of two Trans-European transport networks (TEN-T) Core Network Corridors, North Sea Baltic and Scandinavian Mediterranean (Regulations (EU) /2013). In mid-2020 s the North Sea Baltic TEN-T Corridor will be strengthened by a new Rail Baltica railway connecting Central and Western Europe with the Baltic States up to Tallinn. 1

3 Capitals of both countries are on the opposite side of the Gulf of Finland at a distance of approximately 85 km. The Helsinki-Tallinn ferry line as part of the North Sea Baltic TEN-T Corridor is one of the busiest marine traffic lines in Europe. The sea crossing takes approximately two hours. Further integration of two metropolitan regions is a strategic objective in both countries. The time distance of two hours between the cities, however, forms a limitation to full integration of cross-border services and regional development. In 2016, a series of tenders was carried out for a full economic and technical feasibility study including a tender on the analysis of potential and development of a technical concept for a Helsinki-Tallinn fixed link (FinEst Link) as long-term vision in Finnish- Estonian-Baltic-European connections. The focus of this paper is on the subsea section of the tunnel under the Gulf of Finland and gives an overview of the project and the challenges encountered regarding the technical complexity and various boundary conditions in the design of this ultra-long subsea tunnel. 2. PROJECT OVERVIEW The vision of a railway tunnel between Helsinki and Tallinn - FinEst Link - crosses under the Gulf of Finland and connects the two city centres for passengers and freight. Its objective is to reduce travel time, add mobility and create competitiveness in this area. Therefore, it is planned to integrate the fixed link to the local and national transport network in both countries. On Finnish side it will be connected underground to Helsinki Central railway station, Pasila railway station, Helsinki- Vantaa airport and multimodal transport centre and to the long-distance rail network. In Tallinn, FinEst Link is planned to surface at Iru junction and connect to Ülemiste railway station on ground level. The total length of the fixed link will be approx km. The project location and the horizontal alignment of FinEst Link is shown in Figure 1. 2 Figure 1. Project location

4 FinEst Link is designed as a railway tunnel that connects directly to Rail Baltica railway. Rail Baltica is a planned railway of 1435 mm European standard gauge to be built by 2026 from Tallinn to Riga, Kaunas and on to the Lithuanian-Polish border where it connects to the Western European rail network. The existing rail infrastructure both in the Baltic States and Finland is of wider gauge (1520 mm in the Baltic States and 1524 mm in Finland), which hinders interoperability. Currently, there is no regular international rail service from Finland and Baltic States to continental Europe. Rail Baltica is a strategic project to remove the largest missing link on the North Sea Baltic core network corridor. The visioned transport concept comprises passenger train shuttles, car and truck shuttles as well as conventional freight trains. 2.1 Project organization The Finest link project is a co-operation project of six partners: The Finnish Transport Agency and the Estonian Ministry of Economic Affairs and Communications as representatives from the two countries, the two counties Helsinki-Uusimaa Region and Harju County Government and the two capitals Helsinki and Tallinn. Helsinki- Uusimaa Regional Council acts as the lead partner. The project is divided into the following five work packages: WP1 Management WP2 Comparative Impact Analysis WP3 Technical concept and economic assessments WP4 Benchmarking, policy frameworks and stakeholder dialogue WP5 Communication In the project s governance structure work packages WP2-4, which produce the core contents of the feasibility study, work in collaboration and feed information to each other s processes. WPs 1 and 5 focus on the strategic leadership of the project, stakeholder cooperation, media relations and other communications. TheLINK consortium consisting of Amberg Engineering, Sweco Environmental Oy and WSP Finland Oy was commissioned with the execution of WP3 at feasibility study level. For WP3, the Finnish Transport Agency is the responsible partner on client side. Within the JV Amberg Engineering is responsible for the project management and the construction design and safety concept of the over 100 km long railway tunnel under the Baltic Sea through the Gulf of Finland. WSP is working on the geological-geotechnical assessment, the alignment under the city of Helsinki and the train operation concept including passengers, stations, workshops and freight roll-on/roll-of stations while Sweco covers topics such as the maintenance concept, the strategic environmental assessment and the economic assessment. Additionally Sweco is supporting on local project management and client coordination. 3

5 2.2 Project strategy After free movement of people and goods became possible between Finland and Estonia in 1991 the economic and social interaction between Helsinki and Tallinn has developed rapidly. Several projects in transport and regional development have taken place led by public authorities during the past 25 years. Port authorities of Helsinki and Tallinn have carried out a systematic program of cooperation and investment in several projects co-funded by the EU (e.g. Twin Port I and II). This long-term cooperation paved the way towards signing a joint trilateral Memorandum of Understanding in January 2016 between the two Member States (represented by Finnish Minister of Transport and Communications, Estonian Minister of Economic Affairs and Communication, Acting Mayors of Helsinki and Tallinn, Regional Mayor of Helsinki-Uusimaa and Harju County Governor). The Memorandum stated a joint aspiration of 1) removal of the Helsinki-Tallinn bottleneck in North-Sea Baltic Connection in TEN-T, 2) synchronization of the digital transport services between Helsinki and Tallinn, 3) production of a full feasibility study on Finnish-Estonian Transport Fixed Link, and 4) activities to support pilots on smart digital transport services between Helsinki and Tallinn. In the context of point (3) a pre-feasibility study had already been carried out in 2015 in the Talsinki Fix project. The result of the pre-feasibility study was that a fixed connection between the two cities, with a total construction cost of 9-13 billion euros, could be feasible with public financing of 40% of the total costs. Mandated by the joint Memorandum a project consortium led by Helsinki-Uusimaa Regional Council was formed and co-funding for the project of total 1.3 million euros for was received from the EU S Interreg Central Baltic Program. In total six planning objectives with specific key performance indicators for FinEst Link project were identified: Improvement of the travel service to facilitate daily commuting between Helsinki and Tallinn. The key performance indicators include travel time between the cities ca. 30 min, frequency and ticket price. Smooth travel chains and integration with transport systems. The key performance indicators include integration with national rail networks, Rail Baltica, airports and with public transport systems in both cities. More effective freight transport chains. The key performance indicators are price, frequency, reliability and delivery time. Improved environmental sustainability. The key performance indicators include improved energy efficiency, healthy urban environments and lower emissions of CO2 and NOX. Improved safety and security. The key performance indicator is lowering of risk levels in the transport system. Economic viability. The key performance indicators include that the transport operator s revenues cover all operative costs and that the project implementation requires minimal public funding for the investment. Once in operation, the transport service does not require public support. 4 To reach these objectives the project was identified with the three key values that concern transparency, know-how and stakeholders. All research results, unit costs, calculations of costs, benefits, risks and impacts, and analyses based on them are open and made available for project partners, stakeholders, other transport projects and citizens. Open access to information is applied from the start of the project to its finalization, and always as soon as information is available. Secondly,

6 the project uses highest possible expertise available on large tunnelling and railway projects and their impact assessment. The process is open to new concepts and ideas of how to solve challenges in cross-border transport services. Thirdly, the FinEst Link project welcomes stakeholders and interest groups into the discussion of policy objectives, benefits and external effects of the fixed link already during the feasibility study. 2.3 Tunnel concept and constructional aspects The tunnel layout of FinEst Link consists of two single-track tunnels and one service tunnel with cross passages as shown in Figure 2. Details on evaluation and assessment of different transversal tunnel schemes will be given in chapter 3.1. Figure 2. Tunnel layout for FinEst Link The design of the running tunnels is based on the clearance profile for European standard 1435 mm railway-gauge (according to TSI UIC GC standard). Thus, the two single-track running tubes have a diameter of 10 m. The diameter of the service tunnel is determined to be 8 m in order to allow for space for installations, maintenance incl. crossing of vehicles and safety purposes. A horizontal distance of 70 m between the axis of the two running tubes (35 m between the axis of running tunnel and service tunnel) is taken into account for FinEst Link. During construction, the service tunnel will be excavated in advance of the running tubes. This allows the service tunnel to be used as an exploratory gallery for the main tunnel drives. During operation, the service tunnel is an important part of both maintenance and safety concept of the tunnel. FinEst Link will be mainly situated in competent and stable crystalline bedrock. Approaching the Estonian coast, the crystalline bedrock dives gently under a soft layer of Ediacaran sandstone. The sandstone is a hydraulically conductive aquifer and important groundwater reservoir for Tallinn and surroundings. Overlying the sandstone there is a thick layer of blue clay which acts as an aquitard with very low water permeability. Figure 3 shows the geological longitudinal profile along the proposed tunnel alignment. The vertical alignment of FinEst Link s subsea section will be presented in detail in chapter

7 Figure 3. Geological longitudinal profile Since the construction time is a key parameter in tunnelling, tunnel boring machines (TBM) will be used for the construction of FinEst Link as they offer higher advance rates compared to drill-and-blast excavation. The tunnel sections situated in crystalline bedrock will be constructed either with single shield TBM or double shield TBM. Tunneling in geological formations like Ediacaran sandstone or blue clay requires an active face support in the TBM. Hence, a Mixshield or EPB Shield TBM is deployed for the construction of this tunnel section. For excavation of the cross passages, rescue stations and intermediate accesses drill-and-blast technique is applied. The tunnel is lined single-shell with a segmental lining. The lining is composed of pre-cast concrete segments with a thickness of approx. 60 cm. The segmental ring is designed to bear the rock and water pressures. Segments are sealed with gaskets to ensure the water tightness of the lining even for water pressure exceeding 20 bar. Dealing with such high water pressures is technically demanding. However, there are several references of TBM drives under similar high water pressure like for instance the Follo Line Project in Oslo/Norway (Gollegger, 2013). Should it become necessary, rock grouting works can be executed directly from the TBM in order to reduce rock permeability. 3. TECHNICAL CHALLENGES As part of this paper the focus is set on the following three technical challenges encountered in the design of FinEst Link: Transversal tunnel scheme Intermediate accesses Vertical tunnel alignment of subsea section 3.1 Transversal tunnel scheme Six transversal tunnel schemes were evaluated in a generic way in order to define the best-suited tunnel system for FinEst Link in a plausible and reliable manner. For the evaluation process, the following transversal tunnel schemes were analysed and assessed: 6 A one double-track tunnel with dividing wall B one double-track tunnel and one service tunnel with cross passages C two single-track tunnels with cross passages D two single-track tunnels and one service tunnel with cross passages E three single-track tunnels with cross passages F immersed tunnel with separate cross sections and cross passages

8 For evaluation, a matrix was developed to assess the different tunnel options by using the following seven criteria categories with several subordinate criteria each: Train operation concept Tunnel concept and construction Maintenance and operation Tunnel safety management Geology, ground and rock engineering Strategic environmental assessment Additional functions of the tunnel Evaluation and assessment For decision-making in the assessment of the tunnel schemes, a utility value analysis (a variants analysis based on a scoring model ) was used. This method has advantages in the case of primarily soft decision-making criteria; i.e. those which can be only poorly expressed in monetary or other numerical quantities. Moreover, the benefit can be found in its simple treatment of complex interrelationships, making it possible to achieve direct comparability between different schemes in a short time. The disadvantage is the fact, that the selection and weighting of the criteria are susceptible to highly subjective influences. To overcome this, internal workshops with experts from different fields were held in order to discuss the rating, so that the best solution was defined in a transparent, holistic and traceable manner. In the following, different aspects considered in the evaluation of each (sub-)criteria are presented: In the evaluation of alternative tunnel schemes, the train operational conditions like quantity of trains per day, differences in speed between train types or proportion of passenger and freight trains were regarded to be the same for all schemes. Consequently, the assessment considered how the design of each tunnel scheme may affect parameters like timetable stability, availability or capacity. In addition, the possibility to prolong the subsea tunnel under cities onshore was taken into account. From a train operational point of view, there are no big differences between all the concepts with two separated tracks. In contrast, the single tube-scheme without physical separation generally was evaluated to be poor. The three tube-scheme E was assessed as best overall solution due to the fact that it offers 50% more rail infrastructure than the other schemes. As part of Tunnel concept and construction section, subordinate criteria like construction method suitability, logistics and construction time including risk of delay were analysed. Additionally, construction costs were estimated for all tunnel schemes in relation to each other in order to get a first impression of the cost differences between each type. However, these costs were not considered as an evaluation criteria, but only taken into account for the calculation of the cost benefit ratio. Transversal tunnel schemes D and E with three tunnel tubes are both favourable from a construction point of view as they offer several advantages: A reduced cross section size compared to double-track tunnels, more flexibility regarding logistics and ventilation or the possibility of geological investigation and counteractions in case of difficulties. For the construction of an immersed tunnel a flat bed is 7

9 required. Since the sea floor of the Baltic Sea is very uneven with a very steep section near the Estonian coast, the feasibility of an immersed tunnel solution is highly questioned. Within the maintenance and operation section, the focus was to identify differences between tunnel cross sections in regard to accessibility, need of maintenance and ease of maintenance, e.g. comparing the differences of how fast maintenance operations can be executed and how short maintenance closure times are for each tunnel scheme. A separate service tunnel allows for maintenance activities 24/7 (non-stop all day and night). In option B, the single bi-directional running tunnel requires longer maintenance periods. Considering immersed tunnel variant F it is assumed that concrete structures and seals will need special attention compared to other rock tunnel schemes. In regard to tunnel safety, working safety during construction and self-rescue as well as intervention during operation were evaluated. In addition, other aspects of operational safety like evacuation, impact on other trains or prevention were considered. The analysis showed that variant D is the most favourable transversal tunnel scheme for FinEst Link from a tunnel safety perspective. During construction, a higher number of tunnels offers more flexibility, for instance more means of escape in the event of a fire. During operation, safe areas for escaping persons are of high importance. The service tunnel can be used as a safe haven, which is easily accessible and not part of the operation system. Tunnel schemes with one tube option (A and B) need to have a larger tunnel profile compared to two or three tube options. In case of poor rock quality and fractured zones, the larger cross section is more difficult to excavate and to support and thus more risky for schedule delays and unpredicted costs. A service tunnel with reduced diameter can advance as pilot with a different support concept offering more possibilities for geological investigation or counteractions when tunnelling through weaker geological zones. From an environmental perspective, bored tunnel schemes are with similar environmental consequences. They have some impact primarily to the groundwater quality. Due to geological conditions, this is mainly related to the Estonian side. In contrast, for an immersed tunnel option there would be considerable impact on the aquatic and benthic habitats and ecosystems as substantial areas of the seabed must be touched and sediments relocated. The evaluation of transversal tunnel schemes with respect to additional functions concentrated on the future use of additional utilities. In this aspect, it had to be concluded that tunnel options B, D and E are favourable since new technologies could be implemented in the separate service tunnel. For bored tunnel solutions in general, it is feasible to oversize the service tunnel for possible future demands. 8

10 3.1.2 Results and conclusion A scale of grades, ranging from one (worst solution) to five (best solution) was selected for the assessment of the individual criteria. Linear interpolation was applied between the two grades, resulting in marks from 1 (not suitable) to 5 (excellent). The total score determined for each tunnel scheme was composed of the correspondingly weighted section scores. Table 1 shows the applied weighting factors for each criteria as well as the single ratings of tunnel schemes for different criteria categories. The last column on the very right presents the best solution for each category. As it can be seen, option D is the best solution for most of the evaluation criteria and also the best overall-solution. Based on the estimated relative construction costs for each design, the cost benefit ratio was calculated. It turned out, that tunnel schemes C and D are most favourable, which strengthens the decision made for the best-possible system D. Table 1. Results of evaluation of transversal tunnel schemes In order to make sure that the decision was made in a consistent and resilient manner, the weighting of the section scores was varied within a certain bandwidth to simulate the sensitivity of the system decision with reference to the various project requirements. In a first step, the weighting factor of subordinate criteria within one section was varied (see Table 2). Table 2. Variation of weighting factors of subordinate criteria Tunnel construction In a second step, the weighting factors of the main criteria categories were varied. As an end result, in both cases, it was concluded that transversal tunnel scheme D consisting of two single-track tunnels and one service tunnel with cross passages is the most suitable and best-possible tunnel solution for the planned FinEst Link. 9

11 3.2 Intermediate accesses In the construction of long tunnels it is common practice to use multiple tunnel drives. This is done by means of so-called intermediate attacks in form of access tunnels or shafts which preferably split the entire tunnel in portions of fairly similar lengths. Intermediate attacks reduce significantly the construction time of long tunnels like FinEst Link and thus overall costs. In addition, the provision of intermediate access points is beneficial for: Construction logistics (ventilation, flexibility, accessibility, etc.) Operations (temperature, air quality, drainage, etc.) Safety management Risk mitigation For subsea tunnels, possibilities for providing intermediate accesses are not evident but technically demanding. Olsen (2013) presented a solution using a vertical concrete shaft with top-side superstructure which is common practise in the oil and gas industry. Such a concept was also studied during design works of FinEst Link. However, since there is a lot of marine traffic in the Gulf of Finland, a stand-alone vertical shaft in the sea was assessed to be too hazardous due to the risk of collisions with potentially devastating consequences. Artificial islands offer several advantages compared to platform solutions, namely for instance: The intermediate access to the tunnel system in form of vertical shafts or inclined tunnels is protected by the surrounding island. Thus, the risk of ships crashing into the access connection can be neglected. Harbour facilities can be constructed on an island. As logistics are a key parameter for the construction process, this offers more flexibility and reliability for supplies. The available space on an artificial island can be used for several purposes like temporary material storage (both excavation material and construction material) or installations for waste water treatment, machinery, ventilation, energy, etc. of artificial islands is limited to a certain depth of water. Figure 4 shows a longitudinal profile of subsea section under the Gulf of Finland with respective sea depths. The two locations marked with a black circle were studied in detail as artificial island locations. FIN EST Figure 4. Longitudinal profile of subsea section Figure 4. Longitudinal profile of subsea section 10

12 For FinEst Link it is planned to create two artificial islands at Uppoluoto around 14.3 km away from Finland and at Tallinnamadal approx km off the Estonian coast. They are located in water depths of approx. 20 m and 15 m and will be built with material coming from the Finnish onshore tunnel excavation. During tunnel construction, 6 tunnel drives have to be supplied from each island more or less simultaneously. As space is needed for muck handling, muck deposit, material deposit, silos, batching plants, workshops, offices, harbour and logistic infrastructure etc., a total size of approx. 400 x 300m has been defined as being adequate. Once the artificial islands are created, they serve as launching basis for the construction of the intermediate accesses to the tunnel system. Due to different geological conditions two different sorts of access types will be constructed: On Tallinnamadal island, vertical shafts will be sunk to a depth of approx. 215 m below sea level as thick layers of sedimentary rocks and loose quaternary deposits overlay the crystalline bedrock. For logistical aspects but also for security reasons two shafts are considered necessary. On Uppoluoto island the crystalline bedrock is quite close to the surface. Hence, an approx m long inclined access tunnel with a max. gradient of 10% to ensure heavy truck traffic will be constructed. As the dimensions of the artificial island are limited it is planned to build the access tunnel helix-shaped. The diameter of the shafts as well as the width of the tunnel depend on the equipment and material that are to be transported through the shaft/tunnel both for construction and operational phase. At this stage of the project, a diameter of 10 m is taken into account. During operations, the intermediate accesses will be used for ventilation purpose. Hence, it was decided to locate 2 out of 4 rescue stations at intermediate access points. However, according to the actual safety concept the accesses do not serve as emergency exits for train passengers during operations of FinEst Link. For subsequent use of artificial islands several concepts are conceivable, e.g. the installation of wind power plants or a transfer into recreation areas. 3.3 Vertical tunnel alignment of subsea section The vertical alignment of a subsea tunnel is a crucial design element both for construction and operation. Significant hazard potential is caused by the possibility of high water inflow or even a complete flooding of the tunnel in case of a hydraulic short circuit up to the seabed. To overcome this, a deeper tunnel alignment and correspondingly a larger rock cover is considered in the design. On the opposite, a deeper tunnel alignment causes higher water pressure on the final lining of the tunnel as well as higher energy consumption of the trains to climb up the ramps to the surface. Thus, an optimum balance between these aspects has to be found in the design. 11

13 For FinEst Link, the following requirements were defined and taken into account in the design of the vertical alignment of tunnel s subsea section: The tunnel should be situated predominantly in a geotechnically favourable geology meaning the crystalline bedrock. The rock cover should not fall below 40m at any point of the tunnel in order to avoid weathered zones and geological disturbed zones which possibly could lead to hydraulic short circuits. The maximum longitudinal gradient was determined to be 10 in order to have enough traction especially for heavy freight trains. The minimum longitudinal gradient was set at 5 to allow for a reasonable drainage of the inflowing ground water. Due to the waterproof lining concept of the tunnel, only a minimal amount of water is expected in the tunnel. However, pumping stations will be required in order to transport any incoming water from the tunnel level up to the surface. Since a direct connection to the surface is provided at the intermediate access locations, these points are determined as lowest points of the alignment. Taking into account a min. rock overburden of 40 m and a min. longitudinal gradient of 5, an alignment with a continuous roof pitch between the two lows at the intermediate access points would lead to very deep access shafts but also to a very steep and long ramp up to the tunnel portals. Therefore, an additional low in the subsea section is taken into account. Three low points are justifiable since a waterproof lining concept is designed for FinEst Link. The low points coincides with the positions of the rescue stations. Figure 5 shows the final vertical alignment of FinEst Link s part under the Gulf of Finland. The position of the thee low points are marked with a red circle. Note that for visual reasons in the drawing the vertical distance is three times the horizontal distance. Tallinn / EST Helsinki / FIN Figure 5. Vertical alignment of subsea tunnel section with 3 lows At the deepest point the tunnel runs approx. 215 m below sea-level. Due to the high length of the inclined tunnel section towards Tallinn (approx. 20km), the max. longitudinal gradient of this ramp was reduced to 8.7 in order to lower the energy consumption but also the brake loads. The other subsea tunnel sections have a gradient of 5. On the Finnish side FinEst Link is connected to underground stations, therefore the difference in altitude between onshore and offshore sections is not that high and a design gradient of 5 is sufficient. 12 The vertical alignment of FinEst Link under the city of Helsinki is constrained by existing underground infrastructure. In addition, future construction projects in the area like the planned Pisara underground railway line or the district heat

14 tunnel are challenging in the design of a feasible tunnel alignment. Beside FinEst link project, a new Airport Link (Lentorata project) connecting Pasila railway station and Helsinki-Vantaa airport is currently studied. In next planning phases, the possibility for a combination of Finnish 1524 mm railway-gauge project Lentorata and FinEst Link using European 1435 mm railway-gauge has to be evaluated in more detail. 4. CONCLUSION FinEst Link project is receiving major public attention. A railway tunnel between Helsinki and Tallinn that shortens travel time from 2 hours to only 30 minutes could enable stronger economic and social interaction and enhance regional development in the metropolitan cross-border area. The economic and technical feasibility study concluded that a FinEst Link project is technically challenging but feasible. A transversal tunnel scheme was identified that meets all the requirements from all involved factors. The construction of two artificial islands in the Baltic Sea is a major prerequisite from a construction logistics point of view but also with regard to construction time of this ultra-long subsea tunnel. A vast and complex project such as FinEst, linking two cities with a subsea tunnel of approx. 100 km length certainly is an outstanding challenging infrastructure. Should it ever become reality it will be as a result of innovative and cutting edge engineering and construction technology combined with a sound financing and supported by a strong political will. 5. REFERENCES Regulations (EU) No /2013 of the European Parliament and of the Council Gollegger, J., et al., Follo Line Project, Oslo/N, Swiss Tunnel Congress Olsen, T. O., et al., Ultra-Long Undersea Tunnels, 6th Symposium on Strait Crossings

15 THANK YOU FOR VISITING ITA AITES