Recommendations for shotcrete on rock subjected to blasting vibrations, based on finite element dynamic analysis

Shotcrete is sprayed concrete applied pneumatically on, for example, a rock surface to prevent fallout of rock blocks and thereby securing the arch-shape of a tunnel profile. A finite element model, especially adapted to the dynamic analysis of shotcrete on rock that is subjected to vibrations from blasting, has been developed and tested. The model consists of spring and beam elements that are used to simulate the behaviour of an elastic concrete area, bound to a rock surface through adhesion. This facilitates the calculation of a two-dimensional displacement field, using mode superposition and Duhamel integral. The loads applied on the model are accelerations that give rise to inertia forces on the system. The accelerations are calculated from given weights of explosives, geometrical conditions and rock properties. The presented numerical examples demonstrate the response of shotcrete to vibrations, based on material data from an extensive literature survey. A series of calculations are compiled to give recommendations for how close to shotcrete blasting in rock can be allowed.