The tunnel replacing the Alaskan Way Viaduct (SR-99) will pass beneath 158 existing structures requiring an extensive program of vibration and settlement monitoring as well as some remediation. Of the 158 buildings, WSDOT identified 20 as needing some remediation, but the contractor has shortened that list to 7 structures. For those 7 the tolerable settlement is 1/2 inch, for the remaining, it is 1 inch. Remediation will consist of grouting in at least one case, and micropile walls in other cases where the tunnel alignment doesn’t pass directly underneath the structure. The existing viaduct will also get micropiles for stabilization. Utility relocation and geotechnical instrumentation will take place this year with additional work beginning next year. Tunneling won’t begin until mid-2013 on the $1.4 Billion megaproject. [Source: Seattle Times Newspaper. Image: Storify]
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From ENR:
In the mountains of Peru a tunnel-boring machine named “Pacha Mama†is grinding through the heart of the Andes under rock as deep as 6,890 ft. It is carving away at a 20.2-kilometer-long tunnel through the South American Continental Divide to deliver water to arid coastal farmland.
This is a really interesting project, known as the Los Olmos project, and a nice little article. Normally for a civil tunnel project you drill geotechnical holes beforehand to know what kind of material you’re dealing with. In this case, because of the depth, they don’t have that luxury, so all decisions will be made on the fly. The depth of the tunnel creates some very challenging rock mechanics and logistics problems as well! (Illustration by Odebrecht)