The shield tunneling method is commonly used for tunnel excavation. After the excavation, curved reinforced concrete members are used to support the surrounding ground/rock and seal the tunnel. Grouting is performed to provide adhesion between the concrete members and the ground. The assessment of the grouting quality by pull-out tests and core sampling is destructive, time-consuming and expensive. In the present case, impact-echo was applied as a means of non-destructive and time-effective evaluation. Excitation was conducted by an impact hammer on the surface of several concrete plates and the reflection was acquired by a low frequency accelerometer. Combined use of time domain characteristics, spectral content and wavelet transform reveal the effectiveness of grouting and indicate that impact echo is valuable for quick and reliable assessment of grouting in such cases.
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