Terracon posted a new blog post about a unique hybrid soil nail and anchored soldier pile wall excavation support system for the Tower 12 Building project in Downtown Seattle. The project involves a 60-foot deep excavation for underground parking, but the west side of the excavation was adjacent to an existing 20-story building with three levels of below-grade parking. The hybrid system involved tightly spaced soil nails in the upper portion of the excavation wall and steeply-inclined, high-capacity ground anchors (200 kip) to support the lower portion. Check out more details on this interesting project from Terracon.
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)