Damage of small earth dams for irrigation induced by heavy rainfall
2005
Hori, T.(National Inst. for Rural Engineering, Tsukuba, Ibaraki (Japan))
There are 21.0000 small earth dams in Japan which are important water resources for agriculture. Because they were constructed long time ago, many of them are aged and collapses of these dams, induced by heavy rainfall, occur almost every year. Author investigated these damaged dams and conducted model tests in order to revealed mechanisms of embankment dam's failures induced by heavy rainfall. First of all, damages of embankment dams induced by rainfall are classified into 3 types, such as seepage failure, sliding and overflow. Influences of rainfall precipitation and increase of reservoir level to each type of damages are described. In terms of seepage failure, following mechanism were revealed. Initially cracks occurred in embankments by hydraulic fracturing or some environmental effects. These cracks make permeability of upstream slope of embankments high for a long time. When reservoir levels rapidly razed by heavy rainfall, these cracks open and piping failures occur. In terms of sliding failure, effects of rainfall and filling to stability of embankments ale described. It is considered that large sliding failures likely occur by heavy rainfall or rapid filling. Also, rapid filling causes piping failures, which progress sliding failure of downstream slopes. In terms of overflow failure, conditions of downstream slope surface effect degree of damages when reservoir water overtop on embankments.
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