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<p></p> <p></p> <div><span lang="EN-US">I’ve tried to piece together the bits of information I found in internet about the accident at DB’s Rastatt tunnel. Here are the results.</span></div> <div> </div> <div><strong><span lang="EN-US">The accident:</span></strong><span lang="EN-US"> On August 12<sup>th</sup> 2017 the tunnel partly collapsed where it passed beneath the Rheintalbahn (RTB) mainline leaving a sinkhole and damaged track. One tubbing/lining segment was found displaced by 20’’. The ingress of water and earth spread to a length of approximately 130 feet. Two days before ingress of water was realized behind the TBM’s shield.</span></div> <div> </div> <div><strong><span lang="EN-US">The background:</span></strong><span lang="EN-US">  The tunnel is drilled with a TBM with tubbing segment lining in medium-dense to dense deposits of gravel with various amounts of sand.</span></div> <div> </div> <div><span lang="EN-US">The soil coverage of the tunnel is just 13’ beneath the RTB. To accomplish this, a 7’ thick frozen soil ring was built around the outer diameter (36’) of the tunnel. The freezing process was calculated with ground water temperatures of 50° F, surface temperature of 59° F to achieve a soil temperature of 14° F.</span></div> <div> </div> <div><span lang="EN-US">Freezing for this purpose is a proven building method. New was drilling through the ice ring with ring gap grouting against frozen soil. There were intensive test to find a suitable grout. The grout was tested against frozen soil of -22° F.</span></div> <div> </div> <div><strong><span lang="EN-US">Possible contributing factors:</span></strong><span lang="EN-US"> These are still (educated) speculations, based on photos and statements of DB board members and a not involved expert for railway construction. </span></div> <div> </div> <div><span lang="EN-US">The surface temperature was assumed with 59° F but was at about 86+° F for a few weeks with heavy rains in the days before the crossing of RTB.</span></div> <div> </div> <div><span lang="EN-US">Concrete doesn’t like vibrations while curing. How does freezing soil react to vibrations from 200 freight and 80 passenger trains per day?</span></div> <div> </div> <div><span lang="EN-US">The involved parties check if perhaps freezing with cooled brine instead of liquid nitrogen was the wrong method. </span></div> <div> </div> <div><span lang="EN-US">And there is a disruptive element for the ice ring. If you look at the following picture you see a dark area on the right side the RTB track directly at the intersection, the entrance to a pedestrian underpass: <a href="https://www.baumaschinen-modelle.net/forumsbilder/hansebube/Niederb%C3%BChl_Skizze.gro%C3%9F.png">https://www.baumaschinen-modelle.net/forumsbilder/hansebube/Niederb%C3%BChl_Skizze.gro%C3%9F.png</a></span></div> <div> </div> <div><span lang="EN-US">Here is a picture of the underpass: <br /></span><a href="http://hansebubeforum.de/extern/web/sep10/hccddt3773.jpg">http://hansebubeforum.de/extern/web/sep10/hccddt3773.jpg</a></div> <div> </div> <div><span lang="EN-US">The underpass was filled with gravel and frozen too but its foundation slab reaches up to 3.5’ or more into the ice ring weakening it. Look at the handrails in the picture, you will need them to identify the location in the next pictures:<br /> </span><a href="http://hansebubeforum.de/extern/web/sep10/hccddt3771.jpg">http://hansebubeforum.de/extern/web/sep10/hccddt3771.jpg</a></div> <div> </div> <div><span lang="EN-US">The above photo shows the displaced track and the concrete filled sinkhole directly to the right of the handrails/underpass. The next shows a different perspective:<br /> </span><a href="http://hansebubeforum.de/extern/web/sep10/hccddt3774.jpg">http://hansebubeforum.de/extern/web/sep10/hccddt3774.jpg</a></div> <div> </div> <div><span lang="EN-US">It seems like the damage is beneath the underpass. The underpass was a problem in two ways. It weakened the ice ring and concentrated the usually evenly distributed track loads (at least in 13’ depth) into a smaller area.</span></div> <div> </div> <div><strong><span lang="EN-US">Measures:</span></strong><span lang="EN-US"> The tunnel including the TBM is filled with concrete on a length of 500’. A 395’ x 50’ and 3’-3’’ thick concrete slab is built to carry the RTB across the tunnel.</span></div> <div> </div> <div><span lang="EN-US">After the RTB is in service again the tunnel will be finished. Getting out the concrete won’t be the problem. I think it is a quite soft single-size concrete good to remove with a high-pressure water jet. The TBM perhaps will be cut into pieces.</span></div> <div> </div> <div> </div> <div><span lang="EN-US">I think they try to built the rest of the tunnel using mining technique and sprayed concrete as designed by the owner using the ice ring as stabilization.</span></div> <div> </div> <div> </div> <div><span lang="EN-US">There were several things that might have gone wrong. The tunnel should have been watertight. The ice ring should have prevented ingress of soil as well es water. Why these barriers failed is not known yet.<br />Regards, Volker</span></div> <div><span lang="EN-US"> </span></div>
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