ABSTRACT
River levees occasionally breach during flooding in the mechanics of backward erosion piping and its impact is enormous. Current inspection methods cannot detect the pipe until it manifests at the exterior surface. There is a strong need for non-destructive techniques that can identify progression of the pipe. Okamura et al. (2017) found that small but characteristic deformation appeared on the surface of levees above pipes after a flooding event. They proposed a method for estimating the size and location of the pipes based on the characteristic shape of the deformed slope. In this study, centrifuge tests were conducted to observe evolution of surface deformation as piping progressed. Moreover, this method was applied to a levee along the Naka River, where significant sand boiling occurred at the levee toe during recent flooding events. In addition, a number of penetration tests were conducted at small intervals to identify the pipe locations in a more direct manner. It was found that the penetration tests were effective in detecting the pipe locations. The detected locations compared well with those estimated from the surface topography.
