EFFECTS OF HETEROGENEOUS SPATIAL PERMEABILITY OF RIVER EMBANKMENTS ON SEEPAGE BEHAVIOR

The number of levee breaches caused by intense rainfall and typhoons is increasing in Japan, and the potential for extensive damage is growing.To minimize damage, it is essential to prevent levee breaches or, at least, to lengthen the time leading up to failure.One of the causes leading to failure is reduced stability and deterioration of the embankment due to internal erosion.Previous studies have implicated changes in the strength and stability of embankment soils due to internal erosion.However, the relationship between permeability changes due to seepage and stability is not yet clear.This study conducted seepage tests on an embankment model simulating a river embankment to evaluate the effects of various seepage histories on changes in the hydraulic conductivity and grain size distribution of the embankment.In addition, seepage analyses were carried out assuming spatial variation in hydraulic conductivity due to internal erosion, and the effects on seepage behavior were evaluated.Results confirmed that seepage causes the migration of fine grains, leading to heterogeneous permeability.Furthermore, repeated seepage intensified the fine particle movement within the embankment and reduced the hydraulic conductivity.It was also found that the phreatic surface within the embankment became higher when the permeability of the backslope decreased, whereby the local hydraulic gradient increased.In addition, the results confirmed that the analytical model in this study can express seepage behavior and instability of river embankments over time.