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  Seismic survey using excavation blasting under tunnel construction – TFT Survey at road tunnel construction in Japan

  TFT survey using “Tunnel Face Tester” is a measurement method to be able to record arrival time and wave form of seismic wave occurred by an excavation blasting without interruption of tunnel excavation work. TFT survey is able to evaluate geological condition around a tunnel face using direct waves. At the same time, this is able to predict geological change, for example fault or frac- ture zone, ahead of tunnel face trough analysis of reflect waves. As a result, much geological in- formation can be gotten without interruption of tunnel excavation work. This paper shows outline of the TFT survey, and reports the results of TFT survey conducted in a road tunnel construction in Japan. The changes of geological condition are estimated from the evaluation of direct waves. And the predictions ahead of the tunnel face are conducted, after the characteristics of TFT survey system and the parameters of analysis are reviewed for seismic re- flection. The results of prediction are shown that 66% of the predictions are correspondent to the change of geological conditions.

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