The Use of Steel Fiber-Reinforced Shotcrete for the Support of Mine Openings

What separates the support of mining open­ings from the support of similar civil engineering structures is the fact that mine openings have to survive large defonnations as a result of changing stress conditions induced by progressive mining. Steel fibers impart to concrete and shotcrete a high degree of ductility which not only allows the shotcrete and concrete linings to absorb important rock movements, but also to increase their bearing capacity by a redistribution of the loads.
The use of shotcrete for the support of under­ground excavations was pioneered by the civil engineering industry. In recent years, the mining industry ha,;; become a major user of shotcrete for underground support. The simultaneous working

Steel Fiber Reinforced Shotcrete, It is time to find out about it.

In an age when the building, tunneling, and in some areas, min­ing industry, is thriving in North America, we in the shotcrete industry should be looking for ways to increase productivity and save on ever-increasing labor costs. This type of thinking often requires the use of products that we either are not familiar with or have never used at all. Since we are in an industry where our chief concerns are keeping a safe workplace, while at the same time, trying to increase production or speeding up project comple­tion time, we are often times unwilling to try new technology because we are afraid of the unknown. We fear a decrease in pro­duction, having to buy new equipment, and worst of all, lost­time accidents.For this reason-the unknown-many shotcrete contractors and mine managers have shied away from the use of steel fibers in their shotcrete. Their arguments against using steel fibers are often the same. “We use mesh or rebar for reinforcement because we know for sure that the reinforcement is in place before we apply shotcrete. That way, we don’t have to worry whether or not we have added the correct amount of steel fibers, or if the steel fibers are mixed uniformly, or if the fibers will do the job at all.” Or, we hear the all too familiar response, “If it is not broken, don’t fix it.”
In my opinion, this “if it is not broken, don’t fix it” attitude is keeping a lot of shotcrete contractors from increased production and greater financial successes. Sure, the economy in North America is strong now in the

Evolution of Fiber Reinforced Shotcrete

The concept of reinforcing shotcrete with discrete, disominous steel fibers was developed by the Battelle Research Corporation in the USA in the early 1970s.

Shotcrete Design and Construction for the Stave Falls Project Power Tunnels

BC Hydro has recently completed construction of a replacement power plant at Stave Falls, near Mission, British Columbia. Two new power tunnels were constn1cted to carry water from the intake to the new powerhouse. The crown, walls, and invert of the power tunnels were fully lined with steel fiber-reinforced shotcretc for the primary pur­pose of reducing the hydraulic roughness of the drill and blast tunnel surfaces. Shotcrete was also used for the geometric transition from the horseshoe-shaped, shotcrete-lined tunnel to the circular steel lining.

Shotcrete for Underground Support in Brazil

Shotcrete has been used in Brazil since the 1950s, mainly in minor works of slope stabilization and repairs in concrete structures. It was only in the 1960s that it started to be used in underground work. The Furnas Hydroelectric Project had some sections of its diversion tunnels, where the ground was a highly fractured and weathered quartzite, lined with steel bar reinforced shotcrete. The good per­formance in Furnas led many other hydroelectric projects to adopt shotcrete lining in their tunnels, replacing previously specified cast concrete.

Shotcrete Applications at Northparkes E26 Mine

Shotcrete was used extensively during construction of Northparkes E26 Underground Mine, Australia’s first block cave mine. Applications for the shotcrete included ground support, ground control, construction, safety, protection of equipment and remedial repairs. This article details the various uses for the 16,700 m3 (22,000 yd3) of shotcrete applied at Northparkes, the experiences gained during con­struction, and discusses whether the design expectations have been achieved.

Estimating Volume of Shotcrete for Mining Applications

Traditionally, there has been a rather ad hoc attitude to­wards technical supervision of mining engineering ground control programs, to the extent that the preparation and enforcement of specifications has not been a major issue. In certain locations, however, the dominant use of con­tracting companies to provide mining-related services has meant that structured specifications are needed to ensure the high quality of the end-product. This is perhaps par­ticularly the case with shotcrete (1) now that more and more mines are using the process and product to enhance the ground control regime within the mine.

Shotcrete Reinforcement

Before the 1970s, shotcrete was reinforced either with conventional reinforcing steel welded wire mesh fabric, or in some in­stances with chain-link mesh or even chicken mesh. In the early 1970s the con-Dr. D.R. (Rusty) cept of steel fiber reinforced shotcrete