The 4th River Elbe Crossing Tunnel Project in Hamburg
Diving and Compressed Air Work under Hyperbaric conditions
Shield tunnelling started from the entry shaft on the south side of the Elbe in Waltershof. The tunnel went under the Elbe and the north bank of the Elbe to emerge in the reception shaft in Othmarschen.
The diameter of the TBM was 14.20 metres, making it the world’s largest soft ground machine.
The TBM used was a hydroshield with a combined bentonite/compressed air head. The cutter head consisted of five main hollow box spokes and five subsidiary spokes; it was equipped with 111 picks and 31 ripper chisels. The excavation tools could be replaced either by accessing the extraction space through the access hatches in the main spokes under atmospheric pressure or by accessing the pressurized cutting face directly.
The entire TBM was a staggering 60 metres in length and weighed 2,600 metric tonnes, with the massive 12 metre cutter head alone accounting for 2,000 tonnes.
Three cranes were used to position and fit the cutter head.
A medical treatment pressure chamber 5.5bar was kept in readiness in a container, with a flange on capability for a transport chamber, which in turn was kept operational at all times (transfer under pressure)
The emergency chamber for two people was part of the safety plan; its purpose was to facilitate the removal of injured personnel from the pressurised zone to the surface.
The 4th tube project involved about 3.350 operations under compressed air conditions, logging up a total of about 5.000 hours, most of these in the pressure range between 2 and 3bar, but 80 of them up to 4.5bar. Major insights in this context were; it is possible to carry out and master compressed air work at 4.5bar or 45 m water column (elsewhere such work has been done at 70 m and more); however, it requires careful organization of the medical/technical infrastructure, all the way into the excavation chamber, including in particular man locks to permit rapid provision of medical assistance in an emergency.
It is also essential to train the personnel working in the compressed air surroundings in relevant first aid procedures. There were two workers with a training in first aid under compressed air conditions available at all times, so that they could have entered the chamber through the man lock if necessary.
In the future there will also be digital control methods for compressed air regulation in the decompression process, to minimize human failure.
Constant presence of an experienced compressed air physician will continue to be indispensable in the future.