Development of a simplified seismic tomography survey system

Sugita, Yutaka ; Sanada, Hiroyuki; Aizawa, Takao*; Ito, Shunichiro*

A simplified seismic velocity survey system was developed for the repeat performance of surveys in conjunction with tunnel excavation, to monitor the various changes that occur in a rock mass around tunnels or galleries as they are excavated in the deep underground. The simplified seismic velocity survey system developed consists of a hammer to transfer seismic energy to the borehole wall and receivers installed and anchored in the borehole, and then backfilled. The hammer is operated with compressed air, necessitated by the potential presence of flammable gas such as methane. The system developed was used in the EDZ Experiment in a horizontal tunnel in the Horonobe URL. Changes in seismic velocity were monitored during and after excavation of the tunnel and the tomograms obtained are high quality. These results show that the system developed can provide the information needed to monitor the development and the variations in an EDZ.