The near-surface geotechnical investigations using a surface-wave method become more popular in the last few years. S-wave velocity of ground is directly related to the rigidity of the ground and it can be used to estimate a bearing capacity or liquefaction potential etc. It seems that the surface-wave method can be applied to a lot of geo-technical investigations because the method can delineate two-dimensional Swave velocity structure non-destructively and quickly. Authors are developing a water bottom surface-wave method and carried out field tests in the pond and the river where water depth is about 2m. The result of field tests revealed that an air gun and a hydrophone were suitable as a source and receivers for the surface-wave method respectively. Swave velocity model down to the depth of about 10m under water bottom was obtained by the phase-velocity analysis almost same as survey on land. This paper presents the feasibility study on water bottom surface wave method and the result of field tests performed at the Koyama-ike Lake and the Sendai-gawa River in the Tottori prefecture, Japan.
In Japan, there is a growing interest in renewable energy such as wind power, solar power, etc. these days. As an example of renewable energy facilities, the inshore area is taken into account to construct large wind power plants. We began a study about economical and efficient investigation methods to obtain geotechnical information to design basement structures of wind power plants at inshore areas. Surfacewave method could be one of the solutions for the sake of our study. In order to adopt surface-wave method on inshore area, following studies and experiments were conducted:
Theoretical study to understand the characteristics of surface-wave propagating at the bottom of water,
Water tank experiment,
Field experiments at a pond and a river.