Abstract
TFT survey is a kind of survey that generated seismic waves induced by blasting during excavation. This method allows engineers to carry out a geological survey without interrupting the tunnel excavation work. The geological condition around the face of the tunnel can be evaluated in real time using direct waves. On the other hand, this method allows the prediction of geological changes for instance fault or fracture zones ahead of the tunnel face through the analysis of reflecting waves. As a result, the TFT survey is considered as an advantageous and effective way to obtain various types of geological information.
Furthermore, this paper introduces the outline of the TFT survey and shows the results of the TFT survey carried out during the construction work of a road tunnel in Japan. In this experiment, changes of the geological condition are confirmed from the evaluation of direct waves. The predictions ahead of the tunnel face are carried out after the characteristics of the TFT survey system and parameters of the analysis are reviewed. And the comparison of the TFT survey with other commonly adopted face forward exploration techniques confirming to yield equivalent performance. Results of the experiment estimate that about 70% of the predictions confirm with real geological conditions.
