Vibration vulnerability of shotcrete on tunnel walls during construction blasting

• The effect on shotcrete from blasting operations during tunnelling is studied.
• The effect on young and hardening shotcrete is of particular interest.
• In situ measurement results are compared with results from finite element calculations.
• Recommendations for safe distance and minimum shotcrete ages are given.

The effect on shotcrete from blasting operations during tunnelling is studied, with focus on young and hardening shotcrete. A finite element model specially adapted for analysis of the shotcrete behaviour is tested, it is able to describe stress wave propagation in two dimensions which is important for cases where shear stresses are dominant. The modelling results are compared with in situ measurements and observations, from construction blasting during tunnelling through hard rock. The comparison shows that the model gives realistic results and can be used to investigate the vulnerability of shotcrete, aiming at compiling recommendations and guidelines for practical use. The given recommendations emphasize that blasting should be avoided during the first 12 h after shotcreting and that distance and shotcrete thickness are important factors for how much additional time of waiting is possibly needed.

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