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the additional structural support of the new service throughout construction. The tunnel’s shotcrete ribs, the existing brick liner was able to structural integrity was significantly improved structurally bridge the area between the ribs. In with a solution that was extremely quick (2 to addition to the time saved by using the rib solution 3 days) to construct and readily adapted to the versus using a more typical solution of a 12 in. conditions encountered; allowed the adjacent (300 mm) thick layer of shotcrete over the entire excavation to continue; and, most important, liner, the quantity of shotcrete used was dramatically provided a tunnel able to continue safe passage reduced (refer to Fig. 1 and 2). of approximately 30 trains per day for 6 months The arch shape of the tunnel efficiently carries until trains were able to be placed on the adjacent the external loads pushing on the outside of the new alignment. tunnel by compressive stresses. This allows the In construction, 1177 super sacks of shotcrete, arch to span a large open area and eliminates 25 steel sets with channel lagging, numerous split tensile forces across the arch and the potential for bolts, and many yards of drain strips were cracking caused by tension in the structure. LRL Construction began the work by first removing (scaling) loose brick by hand so that a safe workplace could be provided. The scaling work then progressed with the workers always staying under the previously scaled areas. This technique minimized the risks associated with working under the loose areas of the original tunnel brick. Once the loose brick was removed, the contractor began applying shotcrete. At first, a uniform, thin coat of shotcrete was applied before starting the construction of the ribs. The tunnel, however, had a major seepage of ground water through the tunnel walls and when the shotcrete was applied uniformly, delamination occurred. LRL suggested that shotcreting be staged by first constructing the ribs and leaving the areas between ribs for groundwater to migrate through the brick lining. Once the ribs were complete, drain strips were installed in the areas between ribs. The drainage strips then diverted the flow of groundwater and allowed shotcrete to properly bond in the areas between the ribs. The construction management team and design management teams were pleased with the results obtained using these techniques (refer to Fig. 3). The field-modified construction techniques Fig. 3: Manlifts used to access the arch roof for succeeded, and the tunnel remained safely in scaling, drainage placement, and shotcreting BecOme An AUthOr FOr Upcoming themes: SPRING 2013 SUMMER 2013 Repair & Restoration Training & Certification …as well as Shotcrete Corner, Technical Tip, and more. For more information, contact the ASA offices at: American Shotcrete Association • 38800 Country Club Dr. • Farmington Hills, MI 48331 Phone: 248-848-3780 • Fax: 248-848-3740 E-mail: info@shotcrete.org • Website: www.shotcrete.org Shotcrete • Winter 2013 29


2013WinShotcreteEMag
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