As the soil structure of levee body is often unknown, it is considered as a kind of soil. The boring investigation and the surface wave exploration are used, but they are too expensive to perform at high density. In order to investigate thin surface layer for slope failure, SH type penetration test is used. SH type penetration test can obtain fine penetrated depth until “mm”. In the clay, its wave form between penetrated depth and Nd-value has longer period than sand and gravel. By using spectral analysis for this characteristic, it was possible to distinguish the soil type and visualize the soil composition in the levee body.
