APPROACH FOR FORECASTING DANGEROUS SEEPAGE AREA ON THE DAM SLOPE AFFECTED BY THE TIDE

Abstract

Amplitude of osillation of water table surface and hydraulic gradient under tidal effect, tend to decrease while the seepage flow enters the earthen dam. Therefore, there exists a Dangerous Seepage Triangular Area (DSTA) where hydraulic gradient obtains maximum values. Based on the continuity equation and an assumption on the transmission of seepage oscillation, this DSTA can be specified. Finite Difference Method (FDM), analytical and DSTA methods were programmed using EXCEL software for computation and evaluation of simulated results. The numerical experiments show that the error of total seepage discharge during a tidal cycle between FDM and DSTA methods is less than 1.3%; and the error of maximum hydraulic gradient is not greater than 12%. Besides, the analysis on the earth dam slope stability shows that the most dangerous seepage case occurs when the minimum tidal water level exists as well as maximum hydraulic gradient of out-seepage flow is reached. This is one of the important reasons that explain plenty of tidal river bank erosions in Mekong River Delta.