The Methods for Investigating the Backward Erosion in Cohesionless Soil Foundation

Abstract

The demand of water has been increasing rapidly caused by the population and extension of economic activity while the new water resource project is developed hardly. Under this situation, it seems to force the government agency who take in charge to review inevitably the heightening for the existing reservoirs. The heightening of reservoir with additional water pressure may result in the risk of leakage at dam foundation. The dam foundation comprised with the cohesionless soil (PI < 7) is sensitive to be failed by backward erosion. Even the reservoir has operated for a certain period though the safety of the dam against backward erosion should be investigated. In design stage, the underseepage might be evaluated by the empirical equation of either or by the critical exit gradient proposed. After that gave the adjusting factor for critical exit gradient based on their upward flow tests. Including the physical models showed the resistance of the soil related to the coefficient of uniformity of the soil. These methods are applied for a study cases of Mun Bon dam that had a history of leakage to investigate the backward erosion within the dam foundation. The results shows that the methods of the empirical equation and the critical exit gradient are workable for the well graded and internally stable soil foundation. In the other hands, the method of the physical models conforms with the appearance in the field.