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Transportation can be serious problem for countries, especially, seaside countries or cities that near the sea. During the 20th century, railway transportation has been becoming important particularly for crowded and developed cities due to air pollution, traffic congestion, and so on. Hence, railway transportation systems start to improve.
Times have changed ,however, and what was impressive in the early 20th century, was soon becoming less and less satisfactory. Airplanes and private cars were already offering transportation alternatives at every scale. Given the pressure of competition, the railway had to modernize and improve, especially as regards speed reduction of transportation costs and better organisation and improvement of services offered.
In these conditions, in order to develop transportation systems, Turkish government administrators have started to emphasis on railways. First and foremost, they wanted to find a solution for the traffic problems of Istanbul . It would be possible to cross the sea underground (tube tunnels) or aboveground (bridges). Istanbul currently has two bridges to cross the east-west line but they did not solve the traffic problems. On the contrary, the traffic congestion has been becoming more and more important around the area of bridges. Also this traffic has caused environmental pollution. Turkish government made a decision about undersea tunnel project and started to apply it. The name of the project is ''Marmaray '' and the most significant part of this project is how to cross the Bosporus side. As Balta(2008) stated that the completion of immersed tubes under the Bosporus, part of the project to connect Asia and Europe side of Istanbul through an underground railway, has been praised by Prime Minister Recep Tayyip ErdoÄŸan, calling the Marmaray project, first planned in 1860 by Ottoman authorities, the becoming real of a 148 years dream. Lykke S , Belkaya, H, who are the significant positioned engineers in the project, state that 'the intended purpose of the Marmaray Project is to provide bi-directional, safe, robust, reliable, comfortable, durable, cost-effective and uninterrupted train transportation of passengers and freight throughout the Istanbul area of Turkey, on both sides of as well as under the Bosphorus Strait for a design life of 100 years'.( ITA/AITES Accredited Material Marmaray project: The project and its management,2005)
it will be shown in this paper the background of the Marmaray project in both parts; general background, technical background in the section 2. Then it will focus on the immersed tunnel methods, comparing the other methods, and implemented projects which are used this technique in section 3. After that it will show some review about the method and process of the implementation in the project in section 4 and finally, making evaluation of the overview in section 5.
2. Marmaray project
2.1 General Background of the project
The Marmaray project, which is one of the world's important project, is complex and major infrastructure project being implemented in the world. This project is not the first crossing undersea project in the history. This idea firstly was thought by Sultans of Ottoman Empire, Abdulmecit . In detail, that project consisted of two main structure; several undersea columns and enormous tubes. Also during the Ottoman Empire periods, many of the same projects were prepared. In the year 1902, the most significant project ,Tunel-i Bahri , was prepared. According to this draft, there were 16 columns which were fixed the sea level.
Figure1 : the first prepared projected in Ottaman Empire (sourced from www.marmaray.com)
Until this project started, many projects improved and executed in the different places. Furthermore, project engineers had made various faults. Therefore, project managers have become more experienced over time by evaluating the errors of others. In 1985, Underground transportation systems started to be crucial. And with government support, the first comprehensive feasible study was reported. In 2003-2004, this report was updated for the final model. This project will constitute long term solution to most important problem, transportation of Istanbul. Double lines have a capacity of 75.000 passengers per hour so the traffic congestion will be reduced on the bridges. In connection with this, the air pollution and CO2 release in Istanbul will decrease. Furthermore, according to this graph, while railway usage were 3.6% before the project , Istanbul will reach the developed cities railway transportation usage.
Figure 2: The importance of railway transportation (usage of the railway transportation per 100 people)(sourced from DLH records)
This project offers many different challenges . First and foremost, the immersed tunnel under the sea will be deepest construction with 58m. In this case ,geographical structure was becoming important issue. Throughout the Bosphorus there are two different flow layer ; Karadeniz -Marmara sea , vice versa. Thus, tubes will be affected two sides. The other important one is that construction works can be affect Bosporus traffic, about 50.000 ships using the direction of north- south in the Istanbul strait each year. The last challenge is that the area of Istanbul had experienced seismic event with magnitude 7.5 and it can be evidence about future seismic movement.
2.2 Technical background of the project
This project consist of 4 different part ;
Part 1 : Consultation contract
Part 2 : Undersea tubes and structure of station (BC1)
Part 3 : Revision of substantial train station (CR1)
Part 4 : Getting new railway vehicle (CR2)
Each part of the project is given in a different company which are experts of their field. As it is seen the above, the project divided into 4 different part. This paper will focus on undersea tubes and structure (part BC1) and also it will give some information about the other parts. Nowadays, the part BC1 has just finished and the other parts will be start orderly. In CR1 part, there are 40 stations in this project; 37 of them will be upgraded or rebuilt aboveground , the other three of them will be constructed underground. These stations will consist of centre platform type stations and the minimum platform length is 225m. If peak capacity can be considered ,commuter rail system currently will carry about 10.000 passenger and upgraded rail will transport estimated 75.000 passenger per hour. The maximum operational speed will be about 100 km per hour. Due to the short distance stations, the expected speed will be just 45km/hour. The whole travel time from Gebze to Halkali will be about 104 minutes. During the peak times, trains will leave the station every 120 seconds. (Sourced from ''www.marmaray.com'')
According to the project, the total immersed tube tunnel length is about 1.4 km with connections which is consist of separated two railroad and centre wall. Tunnel was comprised 11 tubes; each tube was about 135m and produced as a prefabrication in Tuzla Offshore Element Fabrication Site. After the production process , each tube was floated to the project location place and immersed by helping special vehicles. Then immersed tubes were connected between them and fixed the sea ground. Figure 3 and figure 4 show to detail of the element 11 which is the part of tunnel and positioned whole tubes plan and profile respectively.
Figure 3: the plan of outfitting for element-11 (Sourced from Minister of transportation record office)
Figure 4 : immersed tube tunnel plan &profile (Sourced from Minister of transportation record office)
3. Analyses of undersea tunnel methods
3.1 Criteria of choosing suitable method
There are several kind of criteria to choice the best solution. In order to compare the different crossing methods ,it is necessary to set an elimination criteria. The most important of these are;
*Although it is theoretically possible to build a particular type structure for every situation, implementation of this can be very expensive and illogical. So many solutions can be eliminated and preferred the best one. This purpose , it is not logical to use tube tunnel methods in shallow water instead of bridges.
*Another criteria can be construction operating, maintenance and repair cost. The total costs of the tunnelling are higher than bridges. Due to the fact that lighting and ventilation. Also the same situation is valid for repair and maintenance. Steel construction which is used for bridge building generally needs more maintenance than concrete structures.
* the user costs can be significant situation for choice of the method, especially vehicles spend time for , fuel and money in traffic. But it is not taken into account because it does not has to be paid by authority providing the money for the link.
* Also safety, Environmental impact( air pollution, noise, visual intrusion) are considerably important.
3.2 Criteria Of The Earthquake And Impact For The Tunnel
Figure 5: Turkey Earthquake Zones Map (sourced from "www.marmaray.com'')
As it can be seen from the map that Istanbul is located in the 20 North Anatolian Fault Zone, which runs from east to west lines of throughout the Marmaray Sea side. It can be seen from the map that the places which are painted red are included most risk and evaluated others ; pink, yellow, white respectively. In the project therefore potential earthquake risks must be taken into the account. Especially during the constructing of underground structures, it must be careful about the safety. In this case, many safety places and emergency exists must be constructed in there.
Severe earthquakes can cause major damage to big infra structure projects if the design does not sufficiently take the effects into account. Therefore, the most sophisticated computer based models will be utilized on the Marmaray Project, and the best experts from America, Japan and Turkey will be involved in the design process.
( sourced from www.marmaray.com )
It could be indicated that the Kobe and BART tunnel located in the most common earthquake zone in Japan and USA. These are good examples of how tunnels could be constructed in a durability. On the Marmaray Project, there were many amassed information from geological, geotechnical, hydrographical and meteorological investigations, and the most modern technologies of civil engineering technology have been used for the design and construction of the tunnels. Correspondingly, More precautions should be taken for earthquake. The most important measure for tube tunnel is that the merging points of the tubes were built with gum elastic. So it can amortise the energy which come off during the earthquake. In this purpose there were many experts from America and Japan involved the construction process and studies. In this part of the project experiences of American and Japan people was used.( partially sourced from "www.marmaray.com")
3.3 Use of Selection Criteria
A monetary value can be determined with many of the criteria. The other criteria can be
divided into many parts ,e.g. noise, and some of criteria can only be assigned a qualitative value. Various systems can be used to appraise these are not comparable worth or at minimum price to provide a way to present them to the decision makers. (Tunnelling And Underground Space Technology, cited in Pera et al 1983)
3.4 the main characteristics of methods
Underwater tunnels are generally preferred places which are not allowed to constructed any type of bridges . There are three alternatives methods for crossing the water ;Bored tunnels, floating tube tunnels, immersed tube tunnels.
3.4.1 Bored tunnel are generally constructed when the ground or waterbed is allowed to excavating and penetration for deep tunnels. In this purpose , there are two main methods could be used. The first one is currently the frequent methods by using Tunnel-Boring Machine is common known TBM method. The other method is that it is commonly known Open -Close method (DBM= drilling- blasting method). However TBM with a circular surface drill soil, it does not create a strong wall. So this method is just suitable for included hard rock. (TCRP Report/NCHRP Report 2006).
3.4.2submerged floating tunnel method is a new style of building method tunnel also known as an Archimed. There are many examples which are built this style in the world. Especially Norwegian and China have implemented project. In this style , the execution places need less substantial sea bed. Tubes are not buried into the sea bed oppositely from the other methods. Therefore, the total project budget could be reduced. Nevertheless ,this methods could be used deep waters due to sea transportation etc.
(Kartaltepe, N,(2008), Preliminary design and analysis for immersed tube tunnel across the Izmir Bay, cited Hakkaart, et al.1993).
3.4.3 An immersed tube tunnels consists of several combined tubes, each often 100 m long, which are built with a prefabricated on the land, that are eventually enlisted below water to become final form. And then each part of tunnel, tubes, are floated and brought to project location by puller ships. In this case, weather conditions as velocity of the wind and stream flow of region are becoming very important. After that ,tubes are becoming lower without physical force. (tubes are lowered with fulfilled the water tank which is embed in the tubes and after finished this operation this water are thrown away from the tubes) Baltzer and Hehengeber claim that it could be risk to locate on the sea beds which include soft sandy, silty or alluvial soils water depth more than 60m. (Kartaltepe, N,(2008), Preliminary design and analysis for immersed tube tunnel across the Izmir Bay. Izmir)
22.214.171.124 Analyses of traffic purpose implemented projects
The technique that was used in the Marmaray project to cross the sea ,immersed tunnel, has been developed since the first part of 20 the century. There are 108 immersed tube tunnels in the world. About their location ,48 of them in Europe, 27 of them in North America, 20 of them in Japan, 9 of them in South Asia(except Japan) and 4 of them in other countries. The first example of the immersed tube tunnels is constructing in Turkey is the Marmaray Project that is being built on the Istanbul Bosporus Waterway. It will be the deepest immersed tube tunnel in the world when the construction is completed(Marmaray 2007).
The firs tunnel which was built for traffic was constructed in USA ,under the Detroit river. It consisted of 11 tubes, each tubes length was 80m and totally tunnel length was 800m. It was built 24 deeper from the surface of the river.
The first immersed tunnel building in Europe was Freidrichehafen, was built in Berlin in Germany in 1927. It consisted of 2 tubes and total length of tunnel was 105.8m. It was shorter tunnel compare with the other examples.
On the other hand, in 1941 , the important tunnel which was currently using as a highway was built in Holland, Mass tunnel. The length of the tunnel is 584m and it consisted of nine tubes. And each tubes 61.35m long, 8.35m in height and had a width of 24.77m. This tunnel was kept closed during the world war 2 by Holland. According to Milestone in Tunnelling: Rotterdam's Maas Tunnel Celebrates its Fiftieth Anniversary ,this tunnel was a landmark in immersed tunnelling due to the fact that its historical significance and technical achievements. Also the most successful designers, engineers, managers and city nation involved this project and contributed to tunnel which exerted excellent standards that still keeps.
It was an important point to notice that pressurised concrete which is used for building more stable structure were used for the first time in the construction of an immersed tube tunnel in Cuba in 1958. The total length of the tunnel was 520 m. The lengths of the tubes average 100 m, the height was 7.10 m. and the width was 21.85. This highway tunnel was built 23 m under the sea level.
The Dees Tunnel in Canada was the first project which is taken account the earthquake
loads was constructed 22 m under the surface of the sea, with a total length of 629 m. It
includes 6 concrete tubes and each ones length was 104.9 m, height was 7.16 m and width was 23.80m. The Scheldt E3 (JFK) Tunnel, built in 1969 in Belgium, had used elements(tubes),
which had ever been constructed of the immersed tube tunnels history.
The width of the prestressed concrete boxes was 47.85 m, height was 10.1 m, while the
length varies between 99 m and 115 m and the weight of each tube was nearly 47000
tons. River currents of up to 3.0 m/s. Tides with a mean range of 4.8 m and a maximum range. So it can be possible to say element's fatigue and corrosion were becoming more and more important.
The Bay Area Rapid Transit (BART) Tunnel was the longest existing immersed tube tunnel in the world. The tunnel was constructed between San Francisco and California constructed in 1970. The tunnel length was 5825 m. and it had been designed as a railway tunnel. This tunnel consisted of 58 tubes and each had a length of average 110 m, and height of 6.5 m, width of 14.6 m. At a maximum depth of 41 m under the sea level, in its time and area it was the deepest tunnel. (Grantz, et al. 1993)
126.96.36.199 Other Applications of the Immersed Tube Method
The execution of the immersed tube method is not limited to crossing the water for traffic purpose , as is demonstrated by the following examples.
1) In 1966 , there was 1600m long metro line was built near the river crossing in Rotterdam. The units, for this purpose, were prefabricated and transported through the artificial canals and used for construction of the station.
2) At Gosport (U.K.), sea outfall into the Solent was built with using the immersed tube method in 1980. Its length was 1.1km.
3) Also in 1985, this method had been used for outlet and intake of cooling water for power plants in Tarragona, Spain.
4) At Karmoy, Norway, The 590-m-long concrete immersed tube method was used for the shore
approach of two gas pipelines. It was created to protect and guide the pipelines through the shore area.
4. DISSCUSSÄ°ON AND RESULT
Transportation is gradually becoming more and more important for both developed and developing countries. As a result, many transportation projects have been applied, especially in European and North American countries. As it is known , Istanbul is the centre of Turkey and the most crowded the city , with 15 million people . The general overview obtained at the end of the study have been evaluated as below
1. This study is based on comparison of the Bosporus sea crossing methods proposed in the Marmaray project and included its background information. Also this study purposed to show challenges and benefits of the project.
2. After the Marmaray project started, the method choosing of the sea crossing was a debatable situation. In this case ,there were three possible methods ; submerged floating, bored tunnel and immersed tunnel methods. According to approved criteria which are cost, quality, durability and so on, if the general usage methods are compared, the best choice can be determined to be immersed tube tunnel. It was the correct choice for these conditions.
3. This paper has investigated a number of different examples of immersed tunnel projects and the condition which need to be met. These are challenges, locations and benefits. Also the decision makers have a chance to compare their work with other projects.
4. The important thing should be notice that potential earthquake loads has been taken into the account and whole project computations have been calculate. Rigorous earthquakes can cause damage on the project. Many computer based models have utilized on the project, and experts from Japan, America and Turkey involved the designed process.
As it is shown that there are three main methods using for sea crossing; Bored tunnel, Immersed tunnel, submerged floating tunnel. Bored tunnel method is used for shallow water. And also sea ground must be firm and not to include sandy, mud soil. The Bosporus side has sandy and mud soil. In this case , it is not convenient method for Marmaray project.
Submerged floating tunnel method is commonly used method last years. It was used first in Norway to cross the river. However, it is not suitable method for Marmaray project due to the project depth, probability of the earthquake and high cost.
The dream of the 146 years Marmaray project and the types of the railway tunnelling methods, especially immersed tube tunnel method, explained in this article about the historical background, developments and usage. There are many examples of the immersed tunnel method in the world, approximately 70 percent of them are located in Europe and North America. In this case, it would be mentioned that this method is used commonly in these area. The one of biggest and still proceeded construction is Marmaray project. This study clearly shows that the most suitable crossing method is immersed tunnel methods for this project.