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2014SumShotcreteEMag

Shotcrete Corner Fig. 1: Construction of original shotcrete backfill barricades involved the use of panels constructed using two layers of welded wire reinforcement, separated with spacers to act a vehicle for the shotcrete. Fabrene was usually Fig. 2: Reduced manpower, reduced cycle time, and improved fastened to the back of the first layer of mesh to water retention soon made the shotcrete process the preferred provide a receiving surface for the shotcrete method for constructing backfill barricades • Reduced manpower; • Reduced cycle time; and • Improved water retention. Process improvements led to many changes in the backfill barricade design. While some improvements were related to cost-reduction initiatives, it was recognized that a structurally sound barricade design was essential in mitigating the risk of a failure. The barricade was constructed in a section of the rock mass that allowed suffi- cient anchorage so that the structural integrity of the wall would not be compromised during the backfilling process. Barricades were designed with a convex curve to properly transfer and evenly disperse the load to surrounding ground. But did it have to be a solid wall? A design concept was drafted by a mining company in the Sudbury, ON, Canada, area, using large, U-shaped troughs made with heavy-gauge sheets of wire mesh and shotcrete (Fig. 3). The Fig. 3: A completed backfill barricade in a northern Ontario mine was perimeter of the barricade would still be mech- constructed using the shotcrete process (note drainage pipes that allow anically anchored with reinforcing bar dowels water to drain from the backfill material) and 24/11 weave Fabrene backed welded wire reinforcement would still be used to create a crete in a predetermined grid pattern as opposed receiving surface for the shotcrete; however, the to a solid wall. entire opening would not have to be sprayed with Further improvements came from the develop- shotcrete. Shotcrete was placed only over the mesh ment of early-age compressive strength testing troughs, which were arranged in a rectangular grid equipment or end beam testers. Compressive pattern. The size of the openings between the strength of the shotcrete material was an impor- U-shaped troughs would determine if the grid tant criterion in determining how soon the back- arrangement would be viable. After a number of filling process could begin after construction of successful tests, it was determined that certain the barricade. Previous test methods for deter- barricades could now be constructed using shot- mining early-age compressive strength of shotcrete Shotcrete • Summer 2014 39


2014SumShotcreteEMag
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