A shotcrete in North American underground mines : Yesterday, today and tomorrow

Abstract

This paper presented a review of the process of guniting, or shotcreting, in North American underground mines. The process can be broken down into the following five distinct parameters: mix design, equipment, logistics, applications and operators. The process of spraying concrete in underground mines began in 1907 and has since become an important part of ground support in modern mining applications and its use and effectiveness will continue to grow. Historically, there have been many stigmas attached to the use of shotcrete in North American mines. The process originally involved the use of dry-mix and placement method using a rotary barrel gun, hand bombed paper-wrapped 50 lb bags of dry-mix, and a very dusty mining environment. The use of shotcrete has steadily increased through the 1980s and 1990s and is currently a vital part of ground control and a dynamic construction tool in mining operations. Annual volumes of shotcrete, both wet-mixed and dry-mix, are estimated to be in excess of 200,000 m{sup 3} in North American mining. The material is moved underground in bulk bags of 1000 kg where it is transported to the workplace for dry-mix spraying. The wet-mix method is used in mines using larger volumes, typically in excess of 3,500 m{sup 3}. The economic benefits of the wet-mix method include a reduction in rebound, higher volume throughput of material and savings in materials handling. Other benefits include consistency in quality and fibre reinforcement efficiency. Mining facilities around the world are also following the trend to wet-mix. In general, mix design has remained the same over the years, but significant improvements have been achieved in the field of concrete/cement stabilization technology. Robotic arms are a major component of today's shotcreting operation as they allow the concrete to be placed efficiently on unsupported ground without ever having to put manpower underground. In addition, industry-wide training programs have dramatically improved the skill levels of nozzlemen and operators. The future for shotcrete in North American underground mines looks very promising. Advances in chemical admixture technology will continue to provide alternatives to mine operators, including the ability to overcome problems associated with poor quality aggregates or to use less costly binders. Automation in equipment will make it possible to control actual application thickness, and to accurately map the applied concrete. 3 refs., 3 figs.