Determination of nonlinear seepage slope for dislocation interface by in situ tests

Seepage failure test means the foundation soil instability caused by underground water perturbation, which is one of the most common methods to evaluate a site seepage resistance, but it is time consuming. High water pressure is always applied to shorten the test time. However, significant error is generated as calculating the seepage failure slope (SPS), the gradient, due to the nonlinear characteristics as the pressure increases. The Darcy law and the permeability coefficient are no longer applicable. Here, an analytical method for confined aquifer is proposed to investigate the nonlinear permeability coefficient and SPS. The in situ tests were conducted on the dislocation interfaces at the reservoir banks of the Baihetan hydropower station to verify the proposed method. The test results indicate that the SPS calculated values by nonlinear equation is much smaller than that by linear equation, which means that the conventional linear calculation results will overestimate the resistance of the site seepage failure. Moreover, the results calculated by steady and nonsteady nonlinear equations are very close, while the storativity is between 1 × 10−3 and 1 × 10−5, which is the ordinary storativity of most aquifers in this region. Hence, in general, the steady nonlinear equation can be used to calculate the site SPS to simplify the calculation.