Change in filtration gradients during head water drawdown

Abstract

Changes in the water level in a reservoir lead to changes of filtration stream parameters in the soil structure. The position of the depression curve, value and direction of filtration gradients and speeds changes near the slope of the structure. Operation practice of waterworks in such conditions shows that emergencies are possible. Changes in filtration stream parameters can cause filtration deformations of soils and loss of slope stability of a soil dam. The article considers unsteady filtration in a homogeneous soil dam for five options of composing soils having various filtration coefficients. The reservoir drawdown rate is considered as an affecting factor. Using the numeric finite-element method and PLAXIS 2D software suite, filtration stream parameters were found for the considered options. Maximum filtration gradients near the upstream slope of the soil dam were found for various options of dam soil permeability and drawdown rate. As the reservoir draws down, directions and filtration gradients and rates change near the slope surface. Maximum gradients occur at various stages of drawdown depending on its speed and reservoir soil permeability. Maximum gradients are quite high, which shows the need for anti-filtration measures.