Abstract
In order to select suitable sites for large-scale structures in mountainous and/or hilly areas, the slope stability of the sites will become an important issue to be investigated and clarified. The loosened rock mass slope generally occupies wide area and has indefinite topographic features, therefore geotechnical investigation in such an area with boring and adits requires large number of quantity and eventually necessitates much cost and time.
In this research, existing refraction seismic data in the downstream area from Tomata dam site are re-analyzed with recently introduced technique of tomograph-analyzing method. The results obtained here are compared with the detailed loosened rock mass condition analyzed by many boring and adits data, we have clarified that specific velocity layer patterns composed of a series of concave structures emerge at the top of loosened area in the rock mass slope. In identifying these specific velocity layer patterns, it is possible to distinguish loosened rock mass slope from rock-mass slide slope, and decrease the cost and time of geotechnical investigation. It is difficult, however, to identify the bottom boundary of loosened area in rock mass slope by using tomograph-analyzing method only. In such a case, this research shows that the borehole-to-surface transmission tomography should be applied to determine this bottom boundary.
