Causes and features of damage to small earth dams induced by heavy rainfall

Abstract

There are 250000 small earth dams, which are important water resource of rural area in Japan. Because the collapse of small earth dams occurs every year due to a heavy rain, it is an important problem for the safety of the area. As a result of rainfall data analysis, dams damage occurred in the area recorded more than 200 mm of accumulated rainfall and more than 20 mm of hourly rainfall. A large amount of hourly precipitation showed a tendency to trigger dams damage. Results of site investigation showed that the type of damage can be classified into overflow erosion, sliding and seepage failure. In the case of seepage failure, internal erosion likely occurs from the upstream slope near the full water level. In the case of sliding, a failure likely starts at a toe of an embankment. Overflow failure likely occurs at the crest above the gut of foundation, because overflowing water concentrate the gut area which is lowered by consolidation settlement.