Drainage Gallery in Concrete Gravity Dams and Its Effect on Reduction of Uplift Forces

When designing gravity dams, engineers consider stability controls such as resistance to sliding and overturning. In addition, allowable vertical stresses at the heel and toe of the dam are relevant parameters. Dam width and height are two important parameters to consider in the design. Other features, such as the installation of a drainage gallery can improve dam stability. In this study, the position of the drainage gallery and its effect on dam stability are investigated. Results show that the relative uplift force (Up/W) in the Outardes-3 Dam without a drainage gallery has a constant value and is equal to 0.413 (where Up is the uplift force and W is the weight of the gravity dam). Reduction of Up/W to 0.14 for installations with a drainage gallery at the dam heel demonstrates the positive effect of drainage galleries. For b/B>0.32, a vertical tensile stress occurs in the upstream heel of the dam. Consequently, this is not recommended (B is the dam width and b is the distance of the drainage gallery from the dam heel). A value of 0.75<B/H<1.0 is suggested (H is the dam height). For such a situation, without a drainage gallery, the safety factor against overturning is close to its maximum values and thus improves the safety of the dam. In terms of vertical stress, with of B/H>0.7, the vertical stress in the upstream heel of the dam is compressive and no tensile stress are generated.