Leakage Problem and Safety Assessment of an Embankment Dam: Investigations and Solution

Abstract

This study determines the reason for embankment leakages of a large dam and demonstrates the importance of site evaluations, aside from numerical seepage and slope stability analyses, to assess whether the leakage observed in the embankment dam is related to seepage from the reservoir or from the groundwater that flows into the embankment. Using the software SLIDE, numerical seepage analysis was performed to determine the seepage pattern and pore water pressures. Results revealed that the calculated seepage exit elevation at the embankment’s downstream shoulder perfectly matched the measured elevation of the leak. Finite element method seepage analyses showed that reservoir water seeped beyond the dam’s chimney filter layer and intersected the downstream slope, which further clarifies that the filter has not functioned well. This study finally puts forth that the leakages are mainly due to the use of a silty sandy soil band together with MH and CH soils compacted excessively on wet side of the optimum moisture content. In addition, through numerical seepage analyses, pore water pressures in the embankment were also calculated for slope stability computations of the embankment. Slope stability analyses showed that safety of the dam slopes is not adequately reliable for even the existing partial impoundment and static loading cases. Thus, this study also suggests that the reservoir water should be kept in an existing partial level and not increased to its designed level. Eventually, the study proposes two remedial measures alternatively and evaluates the best solution.