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Accueil du site → Doctorat → Allemagne → 2019 → Numerical Simulation of Ground Water Flow in Dual Porous Media of the Karun 4 Dam (Iran) Foundation and Abutments

University of Kassel (2019)

Numerical Simulation of Ground Water Flow in Dual Porous Media of the Karun 4 Dam (Iran) Foundation and Abutments

Hosseiny Sohi, Seyed Mohammad

Titre : Numerical Simulation of Ground Water Flow in Dual Porous Media of the Karun 4 Dam (Iran) Foundation and Abutments

Auteur : Hosseiny Sohi, Seyed Mohammad

Université de soutenance : University of Kassel

Grade : Doktor der Ingenieurswissenschaften (Dr.-Ing.) 2019

Résumé partiel
When it comes to the construction of dams and reservoirs in karsts, which are known for their high perviousness due to dissolution faults and conduits, the prevailing risk is water loss. Water loss through basements and abutments of the dams constructed in karst areas leads to considerable costs and non-productivity of the dams. Although the construction of a grout curtain is the most common method to reduce or prevent the water loss, it can solve the problem only partly and in some cases this operation is even fruitless. In this regard, a numerical model, which simulates the dual porous media of carbonate limestone, could prognose the possible water leakage paths. In the present study, different stages to reach this purpose are described for a dam site in Iran as follows : 1) The Karun 4 concrete dam is with a maximum dam height above foundation of 230m the highest dam of Iran. It has been in operation since July 2011. It was constructed over a karst limestone and water leakage has been, and continues to be, one of the most important problems of this dam. The geological formations around the dam site consist of carbonate layers of the Asmari formation and marlstone and marly limestone of the impervious Pabdeh formation, upstream of the dam site. The object of this study is to determine the dam construction effects on the groundwater levels in the adjacent aquifer. Thus, before the dam construction, the natural groundwater levels at both banks were recorded to be 5-8m higher than the river stage. This indicates that the natural groundwater gradient at that time was from the banks towards the river, i.e. the latter was an effluent stream before the construction of dam. At that time no important springs were identified at the dam site., other than a minor spring with a discharge <5 lit/sec that emanated at the contact interface between the permeable Asmari- and the impermeable Pabdeh formation (perching aquifer conditions) on the left bank, upstream of the dam. A Lugeon test that was carried out at that time indicated that the permeability of the adjacent limestone is high, as it varies from 25 to 55 Lu in the layers above the river level, but it decreases gradually to 3 Lu in the formations below. After dam impounding, some changes in the borehole’s water levels were observed. Thus, it has been found, in particular, that the leakage from the reservoir has induced groundwater level rises between 12 to 17 meters. 2) Karun 4 dam is the highest concrete double arc dam in Iran located in the Zagros mountain range in southwest of Iran. It has been under operation since March 2011. The dam foundations and abutments are within the Asmari formation, consisting of fractured carbonate rocks with a high potential of karstification. The water tightness of the dam was one of the main issues during the construction. The grout curtain was constructed to solve the problem in three steps. The object of this study is to evaluate the designed curtain based on the grout taking rate, permeability test, and geological logs. The studied boreholes consist firstly of the exploration boreholes, which represent the structural situation and characteristics of the rock formation, and, secondly of the check holes that were drilled after finalizing the implementation of the grout curtain. The results illustrate the efficiency of the grout curtain, but, nevertheless, some water leakage is still occurring through the curtain, so that further monitoring and treatment is required to ensure the dam safety, namely, to prevent the water leakage.

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