Shotcrete on rock exposed to large-scale blasting

Shotcrete sprayed on rock is vulnerable to stress waves from large-scale blasting in tunnels and mines. Shotcrete support in a Swedish underground mine is studied through numerical analysis and comparisons with previous results, measurements and observations in situ. A previously developed finite-element model that consists of beam and spring elements is used to calculate the response of shotcrete to vibrations from production blasts in the mine. The modelling approach is similar to that of a building during an earthquake, with accelerations measured in situ used as loads. The analysis shows that the calculated bond stresses exceed the strength in the interface between shotcrete and rock close to the blasts. The results show that it is possible to optimise the scheme of the blasting so that shotcrete is protected from damaging vibrations. Also recommended, for practical use, are minimum distances to large amounts of explosives given. This set of recommendations is a supplement to previously given guidelines valid for small amounts of explosives at short distances from shotcrete on rock.