Practical methodology for inclusion of uplift and pore pressures in analysis of concrete dams

Michael McKay, Francisco Lopez (GHD Pty)

Uplift and pore pressures are fundamental loading conditions that affect the strength and stability of concrete dams. Historically, these loads have been difficult to quantify and to implement in finite element analysis (FEA). Some dam design guidelines propose different techniques to apply the estimated uplift pressure for its use in FEA of concrete dams. These methodologies are, in general, quite dated and predominately applicable to simplified 2-D models, reflecting the limited capability of the software and computer power of that time. With the advancement in computer capability and continuous development of FE packages, large 3-D models for all types of concrete dams are not a rarity, and consequently, it is necessary to develop more practical methods to implement and analyse uplift and pore pressure loading in combination with all other loads imposed on the dam. This paper presents a practical methodology for the simultaneous inclusion of uplift and pore pressure in the structural analysis of concrete dams using finite element (FE) techniques. The methodology accounts for the inclusion of a prescribed uplift and pore pressure condition in the FE model, in a way that it can be readily combined with the other loads acting on the dam, and a final effective state of stress can be calculated. This paper presents a worked 3-D example of a generic arch-gravity dam subjected to a static structural analysis, from the initial calculation of the prescribed pore pressure and uplift to the resulting effective stresses in the dam body. 

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