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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MOUNT AIRY, NC—The Univ. of Missouri’s iconic Memorial Union, with its Gothic architecture and central bell tower, was built to commemorate the 117 Mizzou alumni who lost their lives in WWI, and has been under silent attack. Like all buildings built atop the ancient dry riverbeds of the tributary valleys of the Missouri River, the soil beneath is a mixture of sand, clay, and fine rock particles and highly susceptible to erosion from water. So, while hundreds of thousands of students walked the hallways of the building, water escaping steam pipes far beneath caused severe drying of the soil and destabilized it enough so that erosion created voids, or cavities in the soil, some as large as four feet. In turn, this caused the concrete slab floors atop the voids to become uneven, and the eventual danger of even greater problems loomed large.
A team of engineers went after the problem, including MU alums, Matt VanderTuig, P.E., of Bartlett & West, Jefferson City, MO, and Mark Whitehead, P.E. with extensive structural design and environmental engineering management experience. They suggested to Chris Hentges, president of SIRCAL Contracting, Jefferson City, the general contractor in charge of the job, that instead of using the older method of mudjacking, a highly involved and intrusive process of drilling large holes in the slabs—sometimes removing the slabs entirely—and pumping “mud”, ultra-heavy Portland cement-based grout, into the void, then leveling the slabs, that the university might better be served by using the newer polyurethane foam system method called “foamjacking” or “polyjacking.”
[Editor] Be sure to click through for the rest of the interesting project from GeoPrac sponsor NCFI Polyurethanes and TerraThane! [/Editor]