Seismic Performance of Concrete Gravity Dams

Abstract

Dams and reservoirs located near populated areas represent a potential risk in the event of uncontrolled release of the reservoir water due to earthquake damage, endangering the people and properties. In the present work, the seismic performance of concrete gravity dams is studied numerically using commercially Finite Element based software ADINA (Automatic Dynamic Incremental Nonlinear Analysis). The study gives deep insight into the procedure of analysis and safety evaluation of concrete gravity dams, as well as improving its stability under earthquake loading. In the present study, the horizontal component of North Ridge earthquake was selected for analysis. The study covers a range of parameters including the effect of earthquake horizontal acceleration component, substrate soil type and strength properties of soil on the stability of concrete gravity dams. The behavior of upstream water surface under seismic shaking was also considered in the research.The results indicated that the relative uplift force, Ur, is linearly proportion to earthquake intensity. On contrary, Ur, decreases as the relative height of water in the reservoir, Hw/H, increases. The factors of safety, F.S, against overturning and sliding decrease with increasing the earthquake intensity. It was also found that sliding was the governing factor against failure.

Overall Review of Seismic Wave Affected on Gravity Dam

“…Since the dam portion would have been at a height to induce tensile damage near the crest of the gravity dam, Zappitelli et al [10,39] found that displacement quantity was a major impact for gravity dams with a greater downstream slope. The elevation of the gravity dam had an impact on the horizontal displacement of the gravity dam top, according to Zappitelli et al [10,32,54,55]. The gravity dams with the greatest displacement value at the maximum height were the most resistant to bottom limitations, which was because the upper section of the dam was subjected to a bigger impact.…”

“…The researcher showed that raising the magnitude of the earthquake had a 0.04 percent variation in the settling of the gravity dam's body from its stable condition for PGA= 0.1g and elevation of the water/height of the dam (hw/h) =0.25. As the height of the gravity dam was increased to (hw/ h)=0.95, there was a 0.16 percent rise in the quantity of settling [55].…”

“…The researcher said that raising the horizontal component of earthquake improvements might diminish the factor of safety and overturning, as well as, the safety factor in a dynamic condition would be around 50% less in a static condition [23,45,55]. The researcher showed that when the gravity dam on a very stiff clay foundation and exposure to earthquake PGA=0.22g and hw/H increases (due to the rise in the water level), the failure due to sliding occurs with a lower earthquake value, so sliding occurs before the overturning occurs [55]. In the case of (hw/H) =0.25, the overturning would occur at PGA=0.65g, and the sliding at 0.55g, see Figure 8.…”

“…The influence of seismic waves on uplift pressure is a measurement of the total hydrostatic pressure at the dams, according to researchers [52,55]. The water pressure would fluctuate due to a hydrodynamic action throughout seismic event.…”

“…This implies that the rise in dynamics was not the same as the increase in the static state. The uplift pressure was measured at the minimum ratio of (hw/H), indicating that the quantity of uplift pressure would gradually decrease as the height of the water in the reservoir's tail increased [55]. For example, when using (hw/H = 0.25) would notice an increase in the amount of uplift pressure 26.3%, 57.9%, 84.2%, 115.8%, 142.1%, 173.7%, 205.3% and 231.6% with increasing the horizontal earthquake PGA from 0.2 to 0.9 g of an increment of 0.1g.…”