[H-DS07] Landslides and related phenomena

[HDS07-16] Investigation of Shallow Subsurface Structures on Slope using Surface Wave Method

*Yohei Morifuji¹, Yasuto Hirata¹, Kenji Kubota¹ (1.Central Research Institute of Electric Power Industry)

Keywords:shallow landslide, surface wave method

Soil thickness is a significant index to evaluate slope stability. The thickness is usually estimated by dynamic penetration resistance obtained with a standard or simple corn penetrometer. However, much time and labor is associated with conducting the measurement on slopes. Surface wave methods have been used to illustrate S-wave velocity structures relating penetration resistant values, but it is rarely applied on slopes. To verify the effectiveness on slopes, we performed a surface wave method on a hillslope in Yasuura, Kure city. The study site is underlain by the Takada Rhyolite and experienced many shallow landslides due to heavy rainfall in July 2018. Six survey lines were arranged on the slope with 1 m receiver spacing and 1 m source spacing. Three lines were set along the uniformly inclined slope and the rest were arranged to be orthogonal to the three lines. The common midpoint cross correlation method (CMPCC) and the multichannel analysis of surface waves (MASW) were applied to calculate dispersion curves. S-wave velocity was estimated from the dispersion curves using a nonlinear least square method. In the result of the surface wave analysis, a boundary of S-wave velocity was appeared at 2 -3 m depth on the slope. The low velocity area (140-170 m/s) was below the well-known value of soil (Nc=10) obtained by simple corn penetration tests. The S-wave velocity value and Nc were positive correlation in survey lines where the dispersion curves could be calculated. This study showed the efficiency of the surface wave method on slopes, and the distribution of the soil thickness can be more easily estimated than only using corn penetrometers.