The LA Times is reporting that the California bullet train project may be facing significant budget and schedule issues, largely because of a 13.5-mile tunnel beneath Pacheco Pass east of Gilroy. The article reports that the current budget for the 54-mile segment between Gilroy and Chowchilla is $5.5B, but experts that they interviewed for the story put the cost of the twin-bore tunnel itself at between $5.6 to $14.4B. Geological and geotechnical drilling and testing are currently underway for the tunnel which will be up to 1,000 feet below ground through the challenging Franciscan Complex. Don’t forget about the challenges of a seismically active area and at least one major fault crossing. The designers and engineers for that project are going to have their hands full with that one!
The latest information to come out of the collapse of a subway tunnel excavation in Cologne, Germany is that investigators are evaluating the ground anchors or tiebacks that were holding open the subway tunnel excavation. There doesn’t appear to be much information available to the public yet, and the New Civil Engineer article mostly quoted academics saying an anchor failure “could” have caused the collapse. Apparently at the time of the collapse, the excavation had reached the bottom depth after the slurry walls had been constructed along with the ground anchor system. Crews were supposedly working on the base slab which would have undoubtedly stiffened up the whole system. For what its worth, an anonymous comment left at the bottom of that article indicated that after half of the debris had been excavated, the diaphragm walls were still intact and without apparent displacement. So what other theories have been floated? Read on for more info. (Image Credit: New Civil Engineer)