Pore Pressure Development in the Core of Earth Dams During Simultaneous Construction and Impounding
Associate Professor, Amirkabir University of Technology, Tehran, Iran
R. Ahmadi Fard
Amirkabir University of Technology
In some large, and in particular water supply projects, the optimum utilization of the resources and materials often causes the project in some parts go under service before construction is completed. This is common in large dams; impounding starts while the construction of the dam is in progress. Although this will increase the benefit/cost ratio of the project, and make the faster utilization of the project possible, which is of great importance, the adverse effect of such action on the safety of the project in some cases should not be neglected.
In large earth dams the pore pressures within the clay core will appear in some stages of filling. After that stage, it starts developing due to increasing the height of the dam. Usually large pore pressure will develop within the core, when more than half of the dam height is constructed. Due to consolidation process, it normally takes a long time the developed pore pressure dissipates. If impounding the dam parallel to the construction process at this stage is done, the excess build up of the pore pressure within the core may occur due to the head of the water in the reservoir and seeping the water in the dam. This in some condition may lead to excess pore pressure in the core, resulting in hydraulic fracturing of the dam.
In this paper the influence of the impounding of the earth dams on the pore pressure development within the core, while the construction is under progress, is presented. A special computer software (CA2), developed in-house, has been used to model and analyze the earth dam to determine the pore pressure developing due to both impounding and constructing the dam at the same time. In order to calibrate the numerical model, the same geometric and geotechnical characteristics of the Karkheh large embankment dam, recently constructed in Iran, have been taken into account. Since this dam was subjected to the same condition (simultaneous construction and impounding), the analytical results, of the present study have been compared with instrumentation data of the dam, and some important conclusions have been made accordingly.
Keywords: Impounding, Instrumentation, Pore pressure, Construction, Embankment dam, Clay core, Seepage, Consolidation
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