Uplift force, seepage, and exit gradient under diversion dams

Abstract

Correct estimation of uplift force, seepage discharge and exit gradient is very important in stability analysis of hydraulic structures. In this research, by carrying out a set of experiments on a laboratory model, the application of various methods for estimating uplift pressure and seepage discharge under hydraulic structures, and the exit gradient have been investigated. The results show that for the soil type used in the experiments, the method of Khosla et al. gives a better estimation of seepage effects than creep theories. Moreover, compared with Lane's method, it is found that Bligh's theory has better agreement with the observed data of uplift pressure, seepage discharge and piping. By using the finite-element method, the magnitude of pressure head upon a dam foundation in different conditions is calculated, and a relationship between the anisotropic conductivity ratio and the ratio of coefficients in Lane's creep theory is introduced. It is found that while the accuracy of Lane's theory is reduced by increasing the anisotropic conductivity ratio, the new relation estimates the amount of uplift force very well. Based on the finite-element method, a set of graphs is presented to estimate the exit gradient in different conditions with the presence of a cutoff wall at the downstream end or without any cutoff wall.