Session6: Water-related Disaster Risk Reduction
Title: Topographic and Geological Features Involved in Water Leakage at Levee Foundations and in Levee Body Deformation by Piping on the Kakehashi River
Yutaka Sato, Shoji Fukuoka
This study aims to estimate the locations of levee collapse resulting from the piping in foundations, and the mechanism behind such collapse. First, topographic and geological features were investigated on the Kakehashi River. Based on the interpretation of aerial photos taken by the US military in 1947, levee leakage occurred where the present river crosses the former river channel. In the geologic profile along the levee, there was a gravel layer distributed in the foundation. Field investigations quantitatively demonstrated that the seepage conditions there were determined by the relationship between the surface soil thickness and the permeability coefficient of permeable layers. We found that leakage occurred at locations where the surface soil thickness was 3m or less and the permeability coefficient was greater than 10-4m/s. It was also demonstrated that levee deformation from piping in the foundation was mainly controlled by the grain size distribution, thickness and distribution depth of the permeable layers and the embankment load.