Seismic Safety Evaluation Of Sanmenxia Longgou Flyash Dam

The safety of ash dam situated in earthquake regions has always been paid great attentions by designers. Because of the big void ratio and easy liquefaction of fly ash, it is of great significance to investigate the seismic stability of such ash dam with the height over 100m, as Sanmenxia Longgou Ash dam.In the paper, static and dynamic triaxial tests were conducted on fiy ash at Shanmenxia Longgou Ash Dam, and the static and dynamic parameters of fly ash were obtained. Thirdly the 2 dimensions static analysis of the ash dam was conducted based on Biot's consolidation theory and Duncan's nonlinear stress-strain model. Finally the plane dynamic behaviors of the ash dam during earthquake of intensity 7 were analyzed based on the exponent function model of excess pore water pressure aroused by earthquake, which is put forward in the paper, and Equivalent visco-elastic dynamic FEM model and principle of effective stress.The static loads were placed step by step in time sequence in order to simulate the construction conditions of the dam during the calculation. The results of the analysis show that excess pore water pressure would not appear in the design section during theanalysis results that the dam was statically stable and the construction process was reasonable. And the results of the static stress were applied on the analysis of seismic reaction. The variety of pore water pressure with time during earthquake and the distribution of pore water pressure after earthquake were investigated in the dynamic analysis, and the acceleration action process of partial nodes and the shear stress variety process of partial elements were also obtained. The results of the dynamic analysis illuminate that the liquefied area of the dam will be at the top of the coal ash body where coal ash deposits naturally. The depth of the liquefied area is about 20m and the liquefied area is far from the sub-dam, so it does no harm to the dam. Stability analysis indicates that the safety factor of the dam is suitable and sufficient for a seismic design.