Steel fibre reinforced shotcrete: An adequate support for rockburst conditions?

The occurrence of a rock-or strainburst in the immediate vicinity of an excavation results in fracturing and often large displacements of the rock. A rockburst further away from an excavation can still cause heavy damage on mining excavations and tunnels by the passing waves and by the resulting rock displacements. The rock mass is fragmented and ejection velocities of rock blocks can reach 5 to 10 m/sec. Hence, support requirements in mining areas prone to rockbursts should have a large energy absorbing capacity. The support installed should also allow large displacements and a good surface coverage should be provided too. Steel Fibre Reinforced Shotcrete (SFRS) conforms to these support requirements, at least if the fibre content is sufficiently high and evenly distributed, and if the fibres are orientated in all directions. In comparison to plain shotcrete, which is rather brittle, SFRS shows a ductile behaviour and the ability to absorb a significant amount of energy during large deformations. A typical value for a slab of 1 m(2) is 2 kJ. SFRS should be considered as a part of a support system (e.g. in combination with yielding anchors). Attention should be paid to the adhesion between the SFRS and the anchors. Some practical considerations are given to the correct use of steel fibres during shotcreting and a comparison to conventional wire mesh is made.