In underground construction, during excavation of corridor workings (mining) or tunnels, support must be installed to: protect against rock fall and displacement into the working, maintain the assumed cross-section dimensions throughout the entire service life, carry both external and internal loads, prevent loosening, unsealing and weathering of the surrounding rock mass, reduce resistance of medium flowing through the working, and ensure tightness at contact with rock mass.
Currently, several types of support are used for corridor, chamber, and tunnel workings: steel arch, bolt, mixed construction types, segment and tubing (concrete, reinforced concrete), monolithic (concrete and reinforced concrete), and shell support made of shotcrete.
At the current stage of mining technology development, shotcrete shell support has achieved high effectiveness in interacting with rock mass. To improve the load-bearing capacity of shotcrete shell support, it can be used together with dispersed reinforcement — polymer macro fibers (fiber-reinforced concrete).
Shotcrete with macro reinforcement (fiber-reinforced concrete)
Fiber-reinforced shotcrete is homogeneous and has the same strength in all directions. Unlike ordinary concrete, which is brittle, it becomes elasto-plastic. Ordinary concrete loses its resistance to loads after cracking and is destroyed. Fiber-reinforced concrete, however, after exceeding the load that causes the first crack, still has high strength and characteristics of an elasto-plastic material.
Years of experience have shown that it is advisable to use shotcrete in underground construction as: shell support for capital workings (preliminary support and insulating layer behind the face, final support at a greater distance from the face), reinforcement of existing support, and abrasion-resistant material in underground tanks.
Standards and specifications
Shotcrete in mining is produced according to standards: PN-G-14100, PN-EN 14487-1:2006, PN-EN 14487-2:2006, PN-EN 14488-1÷7, PN-EN 14889-1 (steel fibers) and PN-EN 14889-2 (polymer fibers).
We particularly recommend two-component macro fibers: CONCRIX ES 50 and CONCRIX HS 35.