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<p>[quote user="CMStPnP"]Interesting they are tunneling under former swampland of the Rhine River Valley.[/quote]</p> <p></p> <p></p> <div><span lang="EN-US">I think the designation “swampland” is misleading.<br /><br /></span></div> <div><span lang="EN-US">The tunnel is bored in medium densely to densely bedded sand and gravel from the Tertiary and Quaternary. The layers near to the surface are sandy clay and silt.<br /><br /></span></div> <div><span lang="EN-US">The tunnel roof is about 60 ft beneath the surface. The two exceptions are at the ends were the tunnel comes back to the surface.  Parts are built in cut and cover method, the rest as open trough. The minimum coverage of the TBM tunneling is approximately 15 ft. One of these locations is the crossing of the existing rail line.</span></div> <div><span lang="EN-US"><br />To go through with a TBM the soil gets frozen around the tunnel section to between -1°F and -27°F made possible by a high ground water level. </span></div> <div><span lang="EN-US">Here is a longitudinal section: <br /><a href="http://www.tunnel-online.info/imgs/100848247_a568acf19c.jpg">http://www.tunnel-online.info/imgs/100848247_a568acf19c.jpg</a></span></div> <div><span lang="EN-US"><br />What went wrong is not known yet. There are possible scenarios but they would be speculation. I expect a number of contribution factors.</span></div> <div> </div> <div><span lang="EN-US">The SWR, a regional TV station, reports that the tunnel will be filled with concrete on a length of 160 ft sacrificing the TBM worth about $40 Mio.Most important for Deutsche Bahn (DB) is to get the damaged main line back into operation.</span></div> <div> </div> <div><span lang="EN-US">Building subway tunnels in ancient river valleys is quite common. Think of Cologne, Duesseldorf (both River Rhine), Hamburg (River Elbe). In the beginning in Germany with the cut and cover method and after 1955 using TBMs.</span></div> <div> </div> <div><span lang="EN-US">The fourth tunnel tube crossing the River Elbe was built with a TBM while the first three were built with floated in position and lowered concrete elements.<br /> Regards, Volker</span></div>
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