堤体表面沈下分布と貫入試験によるパイピング緩み領域の把握

抄録

River levees suffer occasionally from failure during flooding in the form of internal erosion of soils within or below the levees. It is invisible to current methods of inspection until it manifests itself at the exterior surface. Therefore, there is strong needs to develop non-destructive techniques that can identify internal damage. Okamura et al. (2017) found characteristic deformation appeared on surface of levees just above the piping zone and established a method of estimating the size and location of the piping zone within or below the levees. In this study this method was applied to two levees, Nakagawa and Ushirogawa, where significant sand ejecta appeared at the levee toes during recent flooding events. In addition, closely spaced mini-ram sounding were conducted to identify the locations in more direct way where the soil loosened possibly by piping. The penetration test results were compared with the location estimated from the surface topography to verify the validity of the method.