| Research Abstract |
It is important to accurately grasp the extent of the damaged zone and the level of damage, both for safety management of excavation work and evaluation of long-term mechanical stability of the underground structure. So, a variety of measurement methods have been developed and put into practical use.
We discussed a compact vertical seismic prospecting system using a super-elastic alloy. In the development, we aimed at creation of a system that is reusable without embedding the device in boreholes, facilitating measurement tasks, and that offers useful measurement data. The study presents the application results of the system, and demonstrates that it is easily applied to the management of rock excavation.
The probe, which is the most essential feature of the system, was inserted into holes whose walls were rough, bored with a percussion drill. It was easy to make the vibration sensors incorporated in the probe closely contact the logging hole wall. We confirmed that the extent of the loo
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sened zone in bedrock due to blasting and the P wave velocity in deep bedrock can be readily, yet precisely determined by the seismic prospecting system.
We reported measurement examples in application to the work management of new tunnel construction and control of remaining walls after bench blasting. The seismic prospecting system is equally capable of grasping the existence of weak surfaces and loosened zones in the bedrock around existing tunnels. In the study on the relationship between travel time and transmission distance, we assumed that the P wave distribution is uniform in each zone to calculate the average P wave velocity. However, more detailed analysis of travel time distribution indicates that it is not always uniform. In such cases, by considering the measured velocity as velocity in a specific lot, it is possible to evaluate the inner state of bedrock. Moreover, since the measured wave forms contain information other than travel time, we can obtain further useful data by analyzing them. It can be concluded that seismic prospecting for loosened zones of bedrock around tunnels is an effective technique offering new information, which has not been supplied by conventional logging methods. Less
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