Major Subsea Tunnels: Istanbul 2005

The Open Session for the World Tunnel Conference in Istanbul focused the aspects of sub sea tunnels. Invited speakers presented interesting projects from arould the world, Some projects are still in the early planning stage, some are due to start construction whilst some have been realised. The latter being particulalry projects in the Nordic region. The presentations included projects as the Nusantara Tunnel, connecting Java and Sumatra, the Gibraltar Straits Tunnel between Europe and Africa, several projects in Russia including a crossing of the Nevelsky Strait, the Bering Strait and the La Perouse Strait between Sakhalin Island and Hokkaido Island in Japan. Finally, the Open Session included a comprehensive description of the Marmary project. Altogether, 4 papers presented different aspects of the project:

The Marmaray Project and it’s Management , Requirements of the Istanbul Strait Immersed Tunnel, Marine Operations, the Bosphorus Crossing, Tunnels and stations in BC Contract

The paper reviews the experience from Nordic sub sea tunnel benchmark projects, with main emphasis on sub sea road tunnels excavated in bedrock. More than 25 such tunnels have been built in the Nordic countries, representing a total length of more than 100 km, and with the majority of the projects located in Norway. The completed projects include tunnels with length up to 7.9 km and depth below the sea level down to 264 m. All these tunnels have been excavated by drill and blast. Important issues concerning investigation, planning, design and construction are described, and important lessons learned from these projects are discussed. Finally, plans for potential future sub sea tunnel projects are presented, representing tunnel lengths of up to 24 km and depths below sea level down to 400 m.

The Nusantara TunnelTM as proposed in the paper constitute an interconnected twin tunnel of 33 km long that will be constructed in two phases. Each tunnel is of double elliptical shape with an 8.5-meter flat side and a 6.6-meter vertical height carrying two-way single-track electric car train with maximum traffic capacity of 15,500 passenger-car-units (pcu) per day. The first phase of the tunnel will cost approximately US$ 1.5~2 billion to construct and US$ 4 million per annum for maintenance, operation, and repair. This will require a toll fee of as much as US$ 20 per pcu to travel one-way. The travel time required in making a one-way trip would be approximately an hour.

The governments of Spain and Morocco are jointly carrying out a process of studies on the feasibility of a fixed link between Europe and Africa across the Strait of Gibraltar. Such process is now focussed on a basic alternative mainly consisting in a 38 km-long, 3-tube rail tunnel, functionally similar to the well known Channel Tunnel, i.e. an infrastructure serving both ordinary rail traffic and a shuttle rail system ferrying road traffic between two terminals, one at each shore of the Strait. Fig. 1 illustrates a general layout of such basic alternative, which is expressly subjected to revision in the light of the results of ongoing studies, especially those intended to clarify a number of geological uncertainties and to update a number of functional aspects.

The paper presents a short background and the state of progress of the ongoing studies on the Gibraltar Strait Tunnel, highlighting the aspects related with the singular geo-environment of the Project, which largely governs its engineering and feasibility. The paper takes finally the opportunity to present very recent results from the ongoing 4th Drilling Campaign in the Strait of Gibraltar, one of the most significant landmarks in the study process.

Sustained world economics development trends characteristic with international trade annual growth rate of 7 to 8 % along with considerable dynamics in the interregional goods circulation sphere on one hand and vast territory of Russia combined with a relatively developed railway network on the other hand provide a unique chance for this country to arrange land transportation routes alternative and competitive in comparison with existing marine routes. Construction of rail tunnels seems to be most efficient means for transportation corridors to cross wide water areas like Nevelsky Strait (10.5 km) between the mainland and the Sakhalin Island in Russia, Bering Strait (92 km) between Chukotka Peninsula (Russia) and Alaska (USA). The tunnels construction conditions, structures and technologies planned to be used are considered in the paper.

This paper will discuss the Marmaray Project in its entirety, how the Project is organised, funded and managed. It will also briefly discuss the contract strategies that formed the basis for the final version of the BC1 Contract which is relevant for this conference and which was signed in 2004 and contains the tunnels under Istanbul and the Istanbul Strait including the deep stations at Yenikapi, Sirkeci and Uskudar.

Apart from presenting the Project some management topics mentioned in two of the papers being presented at ITA2005 will be combined and presented at a global level in this part of the session: Marmaray Project, “Project Management” and “Contract Strategy and Minor Tactics”.

This being a design-build project, the challenge faced during preparations of the Employer’s requirements for design and construction of the Istanbul Strait Immersed Tunnel was to give the Contractor as much freedom as possible and yet specify enough so that the Employer obtained the required facility. When completed, this will be a world-class facility. This paper discusses on a strategic level many of the aspects to be presented by the author in two papers in later sessions of the day. Unusual features of this crossing include the deepest ever immersed tunnel crossing, extra waterproofing requirements, strong currents with bi-directional flow, close proximity of the North Anatolian Fault which is predicted to have a major seismic event during the life of the tunnel, and the method of connecting the adjacent bored tunnels to the immersed tunnel. Safety during tunnel construction and operation has been paramount, and resulted in changes to contract packaging and extra requirements. Other challenges discussed include fish migration, control of an international waterway, environmental issues and ensuring the stability of the soft soils during a seismic event.

This paper describes the most important factors influencing the marine regime of the Bosphorus, and present and explain the measurements done up till now in the Bosphorus. It also describes the other constraining fac-tors influencing the immersion processes in the area, and discusses the background for the final requirements to the Contractor related to how to control and predict the marine conditions. It also describes in broad terms the results of the initial investigations performed by the Contractor regarding the immersion process as of the time of writing this paper.

Istanbul is one of the most famous historical cities in the world. However, the Project alignment selected as the best of a range of alignments cannot avoid passing beneath the historical and cultural heritages of Istanbul as well as under ancient and densely inhabited areas of the city. This paper will explain some of the challenges related to the bored tunnels.

Historical buildings are vulnerable. Yet many existing residential and office buildings are old and constructed on minimal foundations. As a consequence, it is vital that any drawdown of groundwater and any ground set-tlements have to be minimized.

In addition, the connection between the immersed and bored tunnels will be made directly and totally under-ground, without the usual intermediate shafts and beneath the deep waters of the Bosphorus Strait. This op-eration needs the utmost control of the tunnel excavation face to ensure its stability and to minimize water in-gress. Based on such considerations, tunnel excavation by Tunnel Boring Machine (TBM) using a slurry shield and having the ability to operate under high pore pressures was recommended as the method of excava-tion for the main running tunnels.

The paper will explain how the design team from Avrasyaconsult – the Employer’s Representative - arrived at the final minimum, specific and functional requirements of the bored tunneling works which are to be carried out using the ‘FIDIC EPC/Turnkey Project’ conditions.