The first 135m long immersed tube element (E11) for the Marmaray rail crossing of the Bosphorus has been placed on the compacted seabed, and the second is about to be submerged in more than 30m of water.
A total of 11 sections, most of the same length, will be placed to form the 1.4km immersed tube tunnel, which will be 58m deep at its lowest point – 17m deeper than the current world record held by BART in San Francisco. Being laid from the Asian side, access to the tube will be restricted to the single, 26m high shaft, weighing 200 tonnes, installed on the first tunnel element, placed in March.
The immersed tube has a cross-section of 15.3m wide by 8.75m deep within which are two cells for single rail running. The tube tunnel has been designed to withstand a Richter 7.5 seismic shock. Therefore, in addition to hydrographical work and dredging, the alignment preparations involved much seabed compaction at the Asian side to avoid liquefaction risk.
Tube elements are being cast nearly 30km along the coast in two specially excavated dry docks at Tuzla, each of which holds two at a time. When a dock is flooded, the elements are towed to near the crossing site and parked for staged placing as preparations are made for the next pair to be cast. The last element (E1) is due to be placed on the seabed, at the European side, in late 2008.
The first of 11 elements of the Marmaray immersed tube being towed out to be placed on the seabed of the Bosphorus. The next is about to be submerged
