Modeling hydrodynamic effects on the dynamic response of an embankment dam due to seismic loading case: Isimba Hydro Power Plant

Abstract

One out of every three embankments dams has failed due to an increase in hydrodynamic forces at the dam fluid-interface. The main goal of this research was therefore to model the hydrodynamic effects on the dynamic response of an embankment dam under seismic loading. Isimba hydropower dam located in Kayunga district was used as a case study. Two dam crosssection D0+D800 and D1+225 in the Right Embankment Dam where studied.

The study first investigated the properties of the various materials used for constructing the dam. An earthquake time history that corresponds to the Isimba dam response spectrum was then developed. Different static finite element models were then built and compared to those previously obtained by the dam contractor. The maximum displacement obtained in this research was 0.1827 while the maximum displacement obtained by the dam contractor was 0.18. The two results were in agreement. The Factor of safety under static loads was also obtained. The result obtained by this research was 1.53 whilst the result obtained by the contractor was 1.55. Again there was agreement between the results. Hydrostatic pressures were also obtained from CFD and compared against analytical hydrostatic pressures. The results were all in a perfect agreement both yielding a maximum pressure of 1.19e5 at the dam bottom and 0 at the surface.

A coupled FEM-CFD model was then developed and used to probe the dynamic response of the dam in a co-execution frame work. A resonant frequency of 0.54 was obtained for the cutoff wall. The overall velocities, accelerations and the displacements of the dam where generally low. Analysis of the plastic equivalent strains showed that the dam wouldn’t undergo any plastic deformation and consequently no permanent deformation. Generally, the dam has sufficient strength to withstand both dynamic and static loads. However, given the low frequency of 0.54Hz of the cutoff that signifies rigidity, this research identifies the region between the dam cutoff wall and the clay as vulnerable to perturbation due to earthquakes. This research therefore recommends that the seepage characteristics between the clay core and the dam cutoff wall be monitored after seismic events to prevent any undesired performance characteristics.