Additional Investigations
Three areas of additional investigation works were identified as being needed in the early phases of the development of the project documents:
- drilling and sampling along the route of the tunnels and stations on land;
- drilling and sampling along the route of the immersed tunnel where it was located underwater, and
- a survey of profile of the bed of the Istanbul Strait along the route of the tunnel.
For these contracts the FIDIC Short Form of Contract, First Edition 1999, was used.
| Contract | Invitation | Award | Completion | Contractor |
| Marine Deep Drillings - Contract 1001 | 18 June 2002 | 2 December 2002 | 22 April 2003 | FUGRO |
| Marine Geophysical Survey - Contract 1002 | 18 June 2002 | 23 September 2002 | 28 November 2002 | Turkish Navy Department of Navigation Hydrography and Oceanography |
| Subsurface Conditions - Contract 1003 | 18 June 2002 | 25 July 2002 | 30 December 2002 | STFA |
It is very important to have good knowledge about the ground conditions in the areas where the immersed tunnel will be positioned in the sea bed. The only way to achieves such information is to make geological drillings, and this has to be done from a barge, a platform or a special vessel. The picture shows the "Bavenit" vessel from FUGRO working in the Istanbul Strait. The drilling rig is mounted on the deck and the ship is equipped with self-positioning systems. This enables the vessel to stay in a fixed position without having to use anchor systems.
The Istanbul Strait is a very busy Strait and it is an international water way. A huge amount of major ships like the one shown on the picture pass through the Strait every year on their way to and from the Black Sea. Furthermore, there is an intense traffic by passenger and car ferries crossing the Strait, so carefully planned safety measures and partial restrictions in the navigation channel will be required during marine operations to maintain a safe marine environment.