Investigation on the Behavior of Maroon Dam during Second Impoundment Using Instrumentation Data

Monitoring the behavior of earth dams during the stages of construction, impoundment and operation is of a great significance. The results obtained from monitoring can be used to check the validity of the design parameters and to improve the design of future dams. Maroon reservoir dam with the height of approximately 170m is one of the highest earth dams in Iran and is located in Khuzestan province in the southwest of Iran. In this dam, various types of instruments such as total pressure cells, piezometers, inclinometers and settlement plates have been installed within five sections to monitor the behavior of the dam. This dam had two phases of impoundments. In the first phase, the water level reached an elevation of 426m, but the reservoir was emptied due to some construction concerns. In the second phase of impoundment which was the main impoundment, the maximum water level reached an elevation of 485m.In this article, the results of three dimensional analyses of Maroon dam during the second impoundment using FLAC3D program are presented and are compared with the results obtained from the instrumentation data. This software involves finite difference method to carry out the computations. The reason for using three dimensional analyses was that the dam is constructed in a relatively narrow valley. Mohr-Coulomb constitutive model was used in the analyses in which the main input parameters consist of cohesion, angle of internal friction, bulk modulus and shear modulus of soil. The dam was modeled in 17 layers each with a thickness of 10m. Considering the actual time of construction, average rate of construction was calculated as 17cm per day. Therefore, for each layer of 10m thickness, 60 days was allocated for consolidation. It is concluded that a rather good consistency exists between the computational results and monitoring results. It is also shown that arching has taken place both along the dam axis and along the upstream-downstream direction; however, the magnitude of the arching has not been to an extent that could cause cracking or piping of the dam.