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Eurasia Tunnel – Bosporus Crossing - Istanbul Strait Road Tube Crossing Project

Hyperbaric Tunneling

Eurasia Tunnel – Bosporus Crossing - Istanbul
Strait Road Tube Crossing Project

Mixed Gas Saturation Intervention at 10.8bar Overpressure

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Client: YMSK JV (Yapi Merkezi & SK Engineering Joint Venture)
Contractor: NORDSEETAUCHER GmbH
TBM Manufacturer: Herrenknecht AG
Saturation equipment: IHC Hytech B.V.
Local sub-contractor: BTT Marine

Project preparation January 2014 – January 2015:

In January 2014, the Saturation Equipment, which was comprised of a Living Chamber (SDC) and two Shuttles (MTS), were built by the manufacturer, inspected and dispatched. At the beginning of April the equipment arrived at the construction site; it was erected in April and May 2014 and, with the exception of a few very minor points, was made fully operational. To achieve this status, it was necessary to develop a system for the Shuttle transport and order a variety of mixed gases. A practice run with the TBM (Tunnel Boring Machine) took place in January 2015 as a final preparation for the subsequent Saturation Interventions. The airlocks in the TBM were initially only equipped for compressed air work with oxygen decompression. The gas distribution and communication system for Mixed Gas Saturation was supplied by IHC Hytech in accordance with the specifications of Nordseetaucher GmbH and was installed in the airlocks.

First deployment phase 05 – 16. June 2014 at ring #126:

On 12 deployment days, 55 hyperbaric interventions were performed and 110 cutting tools were changed and 24 reinforcement panels were welded to the cutterhead. The pressure was 4.2 bar(g), and work was carried out in hyperbaric conditions using the oxygen decompression method.

Second deployment phase 12 – 31 January 2015 at ring #875:

During the first three days, the saturation system was prepared from a generally functional status to get it completely ready for the subsequent deployment; the three-man team, which consisted of saturation divers and technicians, entered the living chamber at the surface close to the access shaft on 15 January and were compressed to a living pressure of 10.0 bar(g), which is the equivalent of a diving depth of 100 m. After a stabilisation phase, the divers/technician were taken in the pressurised shuttle chamber to the TBM following a previously tested transport procedure. Between 15-25 January 2015, eleven interventions were performed in the working chamber at S- 762. Work included closing the submerged wall opening under pressurised conditions and repairing the intake screens under atmospheric conditions. During the course of the work the pipe in the bottom segment was found to have leaks, probably caused by erosion. It was clear that repairing or isolating these leaks would be a time-consuming process. Based on a visual inspection of the stone crushers and suction intake screens and the damage assessment of the NORDSEETAUCHER GmbH divers/technician, a joint decision was taken with the client and the TBM manufacturer to perform the repair under hyperbaric conditions. After installing the central part of the intake screen, the retaining jaws were welded to the main structure because one of the four bolts could not be inserted and it was unclear whether the screws of the other four bolts were completely intact. Subsequently, the isolation procedure was completed in reverse order and the TBM was prepared for tunnelling. Working pressure was 10.8 bar(g) and after a five-day period of decompression, the divers and technician returned to normal pressure at the surface.

An intervention


The control room in the living chamber


The shuttle on its way down the shaft

Transport platform + shuttle on the transport vehicle

Entering the tunnel

Shuttle driving through the tunnel

Transport route in the TBM

Third deployment phase 09 – 25 February 2015 at rings #933 - 962

After a brief preparation period, on 10 February 2015 a three-man team entered hyperbaric saturation. Between 10 and 21 February, eight interventions were performed in the working chamber in TBM S-762 at 10.4 bar(g). Previously, it had been noticed that the stone crushers malfunctioned frequently. The technicians found large steel sheets in the working chamber which were later discovered to belong to the shield edge. The steel sheets were recovered, thermally separated and removed from the area around the stone crushers. After performing a final inspection and functional control of the stone crushers, on 21 February tunnelling recommenced and the team was decompressed to normal atmospheric pressure in a procedure that took four days.


Shuttle transport on the TBM


Shuttle on the lifting platform before docking

Shuttle operator

Shuttle operating panel

Diver and technician in the shuttle

The diver working in the working chamber of the TBM

Fourth deployment phase 05 – 14 March 2015 at ring #1003

The third series of interventions under saturation took place from 05 – 09 March 2015 at 10.3 bar(g). Again, there were signs that the suction system was not functioning properly. The suction intake screen had broken and needed to be replaced. New retaining jaws were attached with longer weld seams. Following decompression, which took place without any problems, the deployment phase ended on 14 March.

Fifth deployment phase 28 – 31 March 2015 at ring #1076

This series of interventions was performed in order to check the working chamber and took place in partial saturation. After a short decompression profile, the engineers were able to ascend to the surface after 2.5 days.

Sixth deployment phase 08 – 15 April 2015 at ring #1117

This series of interventions was required because there was pressure equalisation between the working chamber and the excavation chamber. The leaks were repaired by welding and the excavation chamber, the tunnel face and the cutter wheel were inspected. Three interventions at 8.9 bar(g) were required in total during this phase.

Seventh deployment phase 17 – 29 April 2015 and 06 May 2015 at ring #1147

The left stone crusher arm (VTR) could not longer be operated and was inspected during the first intervention. The bearing and the hydraulic cylinder had broken and the entire stone crusher arm had shifted from its original position. Repairing the damage under hyperbaric conditions was considered but was rejected as being too complicated and time-consuming. Initially, the excavation chamber was checked and then the working chamber was separated from the excavation chamber. The pressure was gradually reduced as the saturation technicians were decompressed. Ten interventions at a maximum of 8.5 bar(g) were required. The actual repair work took place at atmospheric pressure and was performed by staff from YMSK JV and Herrenknecht AG; the work was successfully completed on 06.05.2015.

The subsequent opening of the submerged wall and the preparation of the working chamber for tunnelling was performed in an intervention on 06 May 2015. After a decompression that was free of any problems, the team was demobilised on 11 May.

On 23 August 2015, the TBM broke through to emerge at the other side.

Max. Overpressure 10.8bar

Interventions Start / Finish Work Days Time under pressure
Living under Pressure / Work time
Standard Team 3 Divers/Technicians
January 2015 15.01 – 30.01.2015 Team I 11 1,065:03 243:00
February 2015 10.02 – 25.02.2015 Team II 08 1,086:30 147:00
March 2015 05.03 – 14.03.2015 Team III 05 611:42 92:00
March 2015 28.03 – 31.03.2015 Team IV 01 229:33 07:30
April 2015 08.04 – 15.04.2015 Team V 03 481:18 42:00
April 2015 17.04 – 29.04.2015 Team VI (4 divers) 10 1,015:47 184:30
May 2015 06.05 – 10.05.2015 Team VII 01 269:12 24:00
Team Interventions in Total 07 = 22 Man Interventions
Working Days 39
Time under Pressure 4,759:05
Work Time under Pressure 740:00

Decompression Treatments (Bends) 00