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2014SumShotcreteEMag

Shotcrete Corner The Use of Shotcrete for Construction of Backfill Barricades in Mining Environments By Craig McDonald and Joe Hutter Aore, gems, or other minerals from the backfill material in the stope and allow the watersimilar to that used in the plug. For each step, thebarricade must be strong enough to contain the-s we all know, the mining process is essentially the excavation and extraction of rock, earth’s surface. In an open-pit mining excavation, needed to transport the backfill solution to the the hole in the ground simply increases in size stope to drain. until the resources are exhausted and often a new For many years, the timely and labor-intensive lake will be created by the crater left behind. process of constructing backfill barricades In underground mines, however, as the changed very little. However, as advanced tools deposits are extracted, the voids left behind and technology improved processes in other areas (also known as stopes) must be filled to maintain of the mining industry, engineers began to look the integrity of the surrounding rock or earth closer at the shotcrete process to solve problems mass. If these stopes were left empty, the and improve labor efficiency underground. Shot- stresses from the surrounding rock mass would crete was beginning to play an increasingly result in ground collapses. To avoid these col- dominant role in many areas, including ground lapses, mining companies use a backfill system, support and other forms of underground construc- of which there are many different types, tion. It was not long before the benefits from the depending on the mining method. There is, use of shotcrete quickly expanded to the construc- however, one constant. The entrance point to tion of backfill barricades. the excavation must be blocked and sealed off Construction of original shotcrete backfill bar- using a barricade to contain the backfill material ricades involved the use of panels constructed within the stope. using two layers of welded wire reinforcement, For many years, the underground mining separated with spacers to act as a vehicle for the industry relied on timber for many purposes. shotcrete (Fig. 1). An engineered, high-quality Timber was used to support the tunnels as they coated woven polyolefin-based fabric, 24/11 advanced in length and also to construct barri- weave Fabrene®, was usually fastened to the back cades used to restrict or block the flow of backfill. of the first layer of mesh to provide a receiving Many of the backfilling operations involve a surface for the shotcrete. Reinforcing bar was three-step process, the most important (after fastened to the mesh to provide structural construction of the barricade) being construction reinforcement and dowels were installed in the of “the plug.” The plug is always filled using a surrounding rock to secure the barricade. After higher binder content, which provides a higher- this preparation was complete, shotcrete place- strength backfill mixture to withstand the vertical ment was completed in less than one shift, hydraulic head pressures created by the placement allowing for a significant reduction in cost of the of subsequent backfill steps. barricade, not to mention a reduction in the over- The second step involves filling “the body,” all cycle time of the mining process. a process that uses multiple lifts of a lower binder Because it is the nature of the mining industry content mixture and fills the major portion of to constantly improve processes, it was not long the stope. before the shotcrete barricade was refined. Shot- The third step is to fill “the cap,” a final section crete soon became the material of choice and the of backfill material that uses higher binder content benefits were obvious (Fig. 2): 38 Shotcrete • Summer 2014


2014SumShotcreteEMag
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