On the Optimum Layout of a Drainage Gallery in Concrete Gravity Dams on Isotropic Foundation

This study investigates the optimum location of drainage galleries of concrete gravity dams under usual, unusual, and extreme loading conditions. The uplift and the stress distributions were computed using the gravity method and the beam theory, whereas the leakage rate into the gallery was determined by the finite-element method. The results show that the presence of a drainage gallery can reduce the uplift by over 60 percent compared to a non-drained case. The suitable gallery location shifts toward the upstream if the drain diameter increases and the spacing decreases. This is consistent with previous research. As the gallery is moved toward the downstream, the crack length decreases; however, this increases the uplift. The most effective solution is found to be placing the gallery 10 percent of the base width away from the heel and at the downstream water level or below and adding post-tension cables on the downstream side. This option also yields lower pumping costs by reducing the pump head.