Numerical three-dimensional nonlinear flow analysis is a very efficient instrument for the optimization of the subsurface drainage systems of concrete gravity dams.
Post-mortem optimization analyses of the intake and powerhouse structures of Isamu Ikeda dam indicated that the drains' lengths, spacings and diameters used in design were very close to optimum.
The analyses have also indicated that the uplift force effectively acting at the structures’ base is of the order of 25% of that obtained using the USBR design criterion.
The introduction of an additional drainage gallery together with two lines of inclined drains, in all galleries, would have caused an additional reduction in the uplift force to a value near 10% of that indicated by the USBR criterion suggesting that if the present methodology had been available at the design stage of Isamu Ikeda dam it would have been possible to reduce the concrete structures' weight by nearly 40%.
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