مهندسی عمران شریف (Nov 2019)
EVALUATION OF SEISMIC DEFORMATIONS OF GOTVAND DAM DURING EARTHQUAKE
Abstract
Monitoring and \ evaluating \ earth-rock fill dams in different \ stages of their lifetime including \ construction \ impounding, rapid drawdown and earthquake occurrences \ are important for \ improvement of dam \ monitoring, safety control and stability. Historically, earthquakes have \ caused severe damages and human losses. The destruction of infrastructures, such as dams, is of high concern because of financial and human losses caused by water flowing downstream into densely populated human settlements. Based on the world's earthquake data, rock fill dams showed different behaviors under earthquake conditions, ranging from minor damage and deformation to complete destruction. In the present study the Gotvand dam, one of the largest rock fill dams in Iran has been focused on. In this study, the largest dams' cross-section was modeled and evaluated using two dimensional finite- element software, FLAC4.0. The back analyses results compared with data collected from instrumentation and characterized materials' properties exactly. In numerical analysis, regarding the nonlinear nature of geo-mechanic materials such as soil, the Mohr-Columb constitutive rule and the hardening- softening models used to simulate the material behavior in foundation and dam body respectively. Under elastic conditions, the main assumptions include; 1) increasing the internal friction angle with increasing the plastic strain; 2) dependence of material's elastic modulus and dilation angle on confining pressure; 3) bulk modulus of water dependence in a medium tension stress of the elements during the construction and first impounding to estimate the pore water pressure correctly and saturation collapse simulation during the first impounding. The model was ran for five years after impounding until it reached a steady state. The Mohr-Columb nonlinear constitutive model through Massing-Finn rules was used to simulate the nonlinear and hysteretic behavior of soil and rock materials under earthquake condition. The dynamic analysis is performed to predict the displacement of the Gotvand dam under the maximum credible earthquake (MCE) condition. The type of acceleration time history and the magnitude of input acceleration are also investigated to predict the dynamic behavior of the dam including deformations on the design based earthquake (DBE), the maximum design earthquake (MDE), and MCE. The maximum settlement of the dam core due to application of the Manjil earthquake is equal to 1.94 meters, and the maximum horizontal deformations are 1.30 and 1.19 meters in upstream and downstream shells, respectively. The results showed that the dam deformations were highly influenced by the magnitude of the earthquakes and the acceleration time history.
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