Excavation for the $700M Lake Mead Intake No. 3 Project was put on hold after tunneling encountered a fault carrying groundwater that flooded the excavation and submerged equipment. The flooding occurred over about 4-days, so there were no injuries reported. The Southern Nevada Water Authority ‘Third Straw’ project will secure the Lake Mead water supply for thirsty Las Vegas in the face of declining lake levels. The contractor will drill into the fault and grout it so the water can be pumped out and work can proceed. Check out this interesting SNWA project overview video for the ‘Third Straw’ project. [Source: Las Vegas Sun via ASCE SmartBrief. Image: Southern Nevada Water Authority]
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Devil’s Slide Breakthrough Video and Links
The “breakthrough” media event for CALTRANS’ Devil’s Slide Tunnel project was this past Friday. A large crowd of politicians, news crews and locals were on hand as a road-header broke through a shotcrete face in a ceremony to mark the completion of the excavation portion of the first of two tunnels. It will still be over a year until the tunnels are opened to traffic. The second tunnel is expected to breakthrough as early as this week. (Photo by SFGate.com)
Caltrans tunnel punch-through from Barry Parr on Vimeo.
The Video came from the Coastsider, the page also has comments from the videographer, Barry Parr, which offer a good perspective on the event.
Click on through for more links etc.
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Cologne Tunnel Collapse: Investigations Focus on Tiebacks and Groundwater
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)