Page - 1478 - in Book of Full Papers - Symposium Hydro Engineering

the neighboring areas. It is located on the KOYNA River, approximately 120 miles SSE of Bombay. The existing KOYNA Dam, completed in 1963, is a rubble concrete gravity dam of 853 length and 103 m height. The reservoir has a capacity of 2780×106 m3. Figure 2 shows a schematic model for KOYNA dam (Huang 2011), along with its reservoir and foundation. Results of Seismic Analysis (Case of Full Reservoir) The effect of foundation stiffness on dam horizontal displacements, vertical displacements and normal stress for case of full reservoir is presented in Figure 3. Obtained results show that dam displacements and stresses are very sensitive to variation in foundation stiffness up to EF EC⁄ ratio equals 2.0. For ratios of EF EC⁄ greater than 2.0, no significant effect on dam displacements and stresses is noticed. Figure 4 shows hydrodynamic pressure distribution on dam upstream face at various times during El-Centro earthquake. The figure shows that the hydrodynamic pressure distribution is almost linear at the top 25% of reservoir depth. For the lower 75% of reservoir depth it shows nonlinear trend. Moreover, the shape of the nonlinear part of the hydrodynamic pressure distribution at different times has no specific trend. Furthermore, the maximum observed hydrodynamic pressure occurs at T=0.02 sec. If it is approximated as linear trend it might be about 6% to 9% of the hydrostatic pressure. From the design point of view, the observed hydrodynamic pressure can be accounted for by increasing the hydrostatic pressure by say 15-25% over the entire height of the dam. Figures 5 and 6 show time history for dam displacement, stresses and hydrodynamic pressure for ratios of EF EC⁄ equal 0.5, 1.5, 5 and fixed base case. Obtained results indicates that the maximum horizontal dam crest displacement decreases as the foundation stiffness increases. The time history for horizontal displacement at different heights on upstream face show that all points move in phase indicating essentially that the first mode dominates the response. Figure shows that in case of full reservoir there are tensile stresses at the heel. This already occurred in 1967 when KOYNA dam subjected to KOYNA earthquake and a damage was observed in the actual dam due to tensile stresses at KOYNA dam heel. This tensile stresses leaded to a cracks between the dam body at heel and the rock foundation (Hunjie, 2011). Fehler! Verweisquelle konnte nicht gefunden werden. shows that the normal stresses at the toe are compression stresses at all times and that the behavior is not affected by foundation stiffness variation. But the compression stresses increase as the foundation stiffness increases. Moreover, the foundation stiffness has no significant effect on hydrodynamic pressure at reservoir base. The time history of displacements and stresses show that when the foundation stiffness is five time that the dam concrete, the assumption of fixed base is acceptable. Effect of Ground Motion Excitation To study the effect of different ground motion excitations on the seismic behavior of dam- reservoir-foundation coupled system, four earthquakes are utilized. These are EL-Centro-S00E components, Taft-N21E component, Aqaba-NS component and Aqaba-EW component. While EL- Centro and Taft earthquakes represent severe and moderate earthquakes, respectively, Aqaba earthquake occurred in the Gulf of Aqaba, Egypt, and represent a minor to moderate earthquake. To have a common base for comparison of the dam behavior under different earthquakes, all ground motions were normalized to have the same peak acceleration of EL-Centro. Table 1. Shows values of peak accelerations and the factor of normalization for each earthquake. Table 2. Shows the effect of four earthquakes; on KOYNA dam displacements and stresses. Obtained results show that EL- Centro earthquake-S00E component caused the minimum displacements and stresses, while Aqaba- EW earthquake resulted in maximum displacements and stresses. Figure 7. Shows spectral 1478