As a technique to cross the Bosphorus Strait, the owner side designated the submerged tunnel method, but it was the first attempt at a depth of 60m in the world.

The flow velocity in the Bosphorus Strait from the Black Sea side is usually 1-2m/s (maximum velocity of 3m/s) in the surface level, and underneath there is a flow (1m/s) in the opposite direction, causing a complex tidal current. Furthermore, there are no regular "tidal stops" caused by the tide in the Bosphorus Strait, and changes in wind and air pressure cause sudden changes of 2m/s and higher in the surface level every few hours, making an extremely harsh environment to implement the submerged tunnel method.

To combat these restrictions, Japanese engineers had compiled precise data including water level, flow velocity, wind direction and speed, and air pressure from more than one year before the start of construction to work up a plan to be able to avoid the high flow velocities in when submerging. Furthermore, based upon this data they newly developed an "Information Communication Technology (ICT)" which estimates future flow condition changes in a few minutes. Also, the submerged culverts were guided to the sea bottom using positioning combining GPS rotating multi-beam echo sounders, gyro-compasses, and angle meters, and in the final stage when the submerged culverts were joined, a "Submersion System" was developed to measure and control with high precision ultrasonic measurement equipment. Through these systems, the submersion of all the submerged culverts was completed within the planned period, and it was accomplished within the precise limited range (within 8cm) for installing the submerged culverts.

An issue which differs from the tidal currents is that because the shallow sea terrain is spread out in the bedrock on the bank of the Bosphorus Strait, the construction of departure shafts, which are generally necessary in constructing submerged tunnels, would require a great deal of time and funding. As a means to resolve this issue, Japanese engineers proposed constructing a submerged tunnel in the offshore section 350m from the bank on the Asian side and 200m from the bank on the European side and connecting the submerged tunnel edges on both sides with a shield tunnel underwater. Also, fitting with this construction method, after the initial submersion of the submerged culverts they installed temporary shafts (access shafts) directly upon the submerged culverts to secure an access route into the submerged tunnel culverts (see Figure 3). Through this construction method of not using departure or arrival shafts, a reduction of the construction period by one year and construction costs by 10% were realized, compared to traditional methods.

The same as the submerged tunnel method, it was designated by the owner side to use the shield tunnel construction method for the tunnel parts outside the Bosphorus Strait as well. Also, at a depth of 60m and being the place where the submerged culverts were backfilled, the work had to be done under extremely high pressure. And so in order to handle the places with the most severe conditions, an airtight muddy water type shield method was adopted. In the general shield tunnel construction method, excavation is conducted while exchanging/inspecting the bit (a disc-shaped disc cutter) on the front surface, but in this project an airtight type was adopted. Furthermore, everything other than the joined part was hard bedrock, so there was no option but to construct a long distance (approximately 14.6km) bedrock via an airtight shield tunnel construction method. Such a long distance bedrock being constructed via an airtight shield tunnel construction method is a rare experience even in Japan.

Also, because Turkey is an earthquake-prone country, igneous rock has penetrated into the sedimentary rock, and the surrounding area has been subject to thermal metamorphism and pressure metamorphism by magma and become clay and boulders. Therefore, places where hard layers and soft layers appeared alternatingly and places where the granularity was different from the bedrock with a great deal of boulders, clay, and crevices were seen every 50-60m, where short, and even every 200m, where long. In the muddy water type shield method, in order to maintain a fixed pressure, it is necessary to excavate while changing the properties of the muddy water. As a result, the longer the distance, the more time it takes to change the properties of the muddy water and send it to the edges. Additionally, in the bedrock with many crevices, the crushed bodies are larger than expected, and so they get stuck in the pipe when sending them to the bank, creating the risk of blockage, sudden rises in pressure, and damage to the equipment.

And so the following improvements were implemented, improving the excavation speed.

1) Remodeling of cutter face
Because wear on the external disc cutter is especially rapid, the intake openings and external disc cutters were expanded and increased in size.

2) Improvement of fluid equipment
In order to prevent blockage and reduce the removed earth load, 2 rotary crusher units were serially installed where there was 1 unit originally, and the size of the crushed bodies of removed earth were made reliably smaller.

3) Improvement of muddy water processing equipment.
In fitting with the mud removal capacity, the muddy water processing capacity was also improved.

4) Reinforcement of personnel
The efficient exchange of parts, etc., was implemented by organizing a maintenance group with experienced Japanese supervisors to conduct regular inspections and periodic maintenance.

The implementation via an EPC (Engineering Procurement Construction, a form where design, supply, and construction are implemented comprehensively) agreement can be highlighted as a characteristic which differs from the technological side. EPC agreements are normally applied where the construction risk is foreseeable in advance such as power plants constructed above ground, and would not essentially fit with this project where the construction is mainly underground. However, because the owner placed the order as an EPC agreement, the contractor had various obligations imposed upon it, such as fluctuating astronomical, hydrological, and ground condition risks, design liability, and equipment and quality assurance.

It was determined that the contractor would bear these risks and responsibilities, but the text of the agreement included clear and unclear things, so it was predicted that some differences of recognition and understanding between the parties would arise. Therefore, although the agreement form placed most of the risks upon the contractor, in order to arbitrate various agreement disputes and emergencies fairly a dispute arbitration committee was established. This committee consisted of one chairperson and 2 members for a total of 3 people, and their decisions were contractually effective. It was also possible to make notification of objection to the decisions of the committee and petition for mediation to the ICC (International Chamber of Commerce).

This project is still currently under construction, and at this point about 50 matters of dispute have been brought to the dispute arbitration committee. Examples such as construction period extension and costs caused by the historic ruins survey delay, responsibility for measures to handle frail buildings, and indirect expenses of design change construction were brought forward and resolved.