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2014WinShotcreteEMag

applications, providing an excellent finished product while stabilizing hillsides with complex geotechnical issues. One without the other would provide subpar reinforcement, but together, they provided the best possible combination for strength and stability of deep-cut walls. Nicholas J. A. White,* Engineer of Design, stated, “Prior experience with Ringler’s team on many other challenging projects made his team the only one considered to be qualified and capable to take on a project of this magnitude and complexity.” Ringler’s work on this project included all of the shotcrete work for the installation of approxi- mately 65,000 ft2 (6000 m2) of permanent soil nail retaining walls for the reclamation of the old rock Fig. 3: Completing lowest level quarry. Work included in the reclamation plan was the stabilization of the perimeter quarry wall faces, which were up to 75 ft (23 m) tall, while coordi- nating with the new site development plans. The owner of the quarry, W. M. Rickman Con- struction Company LLC, used quarry soils to provide a series of access roads and work platforms at varying heights to reach each level as required to construct each element of the retaining walls. The design and construction of the soil nail wall system was done by Wolverine Contracting, Frederick, MD. The technique was used to build a “top-down” retaining wall system. As soil nail walls are built from the top down, they provide temporary and permanent earth support in a single-wall system. There was not enough room Fig. 4: Access roads were built and drilling commenced, closely followed on this project to over-excavate to build conven- by nail grouting and wire mesh installation tional cast-in-place walls. If conventional walls had been used, there would have been extensive sheeting and shoring required to provide safe conditions for wall construction. The soil nail wall system was a great success on this project, saving the owner a considerable amount of money when compared to other wall systems that were considered. The walls on this project were terraced, with each wall ranging from 10 ft (3 m) to more than 20 ft (6 m) tall when completed. The soil nailing process requires working in soils which will self-support over the short-term from 4 to 5 ft (1.2 to 1.5 m) tall. The residual soils, disintegrated rock, and bedrock at this site were a good fit for soil nailing. The general method of construction was to start at the top of the top wall in a given area and make a 5 ft (1.5 m) deep excavation to the back Fig. 5: Soil nailing face of the new wall. Then, soil nail anchors were drilled and grouted in the exposed face. handle any seepage behind the shotcrete. Next, The nails used on this project were epoxy-coated a layer of wire mesh was installed and a layer high-strength all-thread steel bars. The nails of dry-process shotcrete at least 4 in. (100 mm) were grouted into 4 in. (100 mm) diameter holes thick was sprayed over the cut face. This layer drilled back 20 to 40 ft (6 to 12 m). The nails of shotcrete is referred to as the temporary layer. were typically installed at 5 ft (1.5 m) vertical Once testing of the soil nails was complete, the and 6 ft (1.8 m) horizontal centers. Chimney excavation was continued 5 ft (1.5 m) deeper drains were installed at 6 ft (1.8 m) on center to and the process repeated. Shotcrete • Winter 2014 45


2014WinShotcreteEMag
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