Development of Pseudo-Static Method for Stability Analyses of Embankment Dams with egard to Foundation Effect (Case study: Masjed Soleiman Dam)

Pseudo-static method is one of the oldest and simplest techniques for seismic stability analysis of embankment dams. Selection of appropriate seismic coefficients is the foremost part of analysis in Pseudo-static method. Previous researchers and design manuals often suggest constant values for selecting the seismic coefficient, regardless of geometry and stiffness of foundation and the dynamic characteristics of the structures.
In the proposed method, the seismic coefficient is a function of parameters α and β. Parameter β is indicative of acceleration amplification in the direction of the dam height, and is related to the geometrical specifications and material properties of the dam body and foundation. Therefore, β can be obtained through dynamic analysis. In this research, in order to obtain the effect of foundation on this parameter, a geometrical model of the Masjed Soleiman Dam has been analyzed dynamically using seismographs of earthquakes that occurred in different sites. Dam consultants used this value for the MDE of the Masjed Soleiman Dam site. Parameter was obtained by assessing the way in which the maximum acceleration varied at different points on the height of the dam. Also, the effect of far and near field records of earthquake are evaluated.
In this research, the safety factor in a wedge corresponding to the seismograph that causes the allowable displacement in that wedge is assumed to be equal to one. Thus, available seismographs were scaled to peak acceleration values and, using them, the wedge displacement values were calculated. The safety factor changes were then calculated using the seismograph that caused the allowable displacement in the wedge. These safety factors were assumed to be equal to one, and the dynamic safety factor for each wedge was determined by comparison of the results obtained from the original seismograph.
After comparison of the dynamic and pseudo-static safety factors, the desired safety factor was determined. The distribution of the horizontal acceleration corresponding to the safety factor was compared with the linear distribution of horizontal acceleration proposed in this article and the values of β were determined. Finally, a new technique to estimate the pseudo-static seismic coefficient is presented. Different conditions for foundation are assumed and results of analyses are evaluated. Results of this research imply that geometry, stiffness and analyses have been compared and based on the comparison of axial forces in the nails (as the most important factor of the stability), the equivalent horizontal acceleration coefficient for the model is proposed. The applied forces cause the reinforcement tension and the mobilized tension force can overcome the soil tension weakness. Thus, predicting mobilized forces in soldier pile nails during earthquake is very important.
The effects of most important parameters such as wall height, nail arrangements and soil types through numerical modeling of the soldier piles under dynamic loading by using FLAC have been investigated.