Experimental study of the effect of hydraulic gradient on soil hydraulic conductivity

Abstract When operating various hydraulic structures, particularly agricultural drains, during the water movement through soils, various types of suffusion deformations typically occur. Particle reorientation and displacement happen under the influence of various forces, including hydraulic gradients. The movement of fine particles, mechanical suffusion, and colmatage were investigated in the hydro-technical laboratory of the National University of Water and Environmental Engineering (Rivne city). Laboratory experiments on filtration using Darcy’s facility reveal patterns of the hydraulic gradient’s influence on the hydraulic conductivity in soils with different particle size distributions. The article describes the experimental facility and filtration model, outlines the selection of model soil compositions, and the corresponding experimental constructions, along with the conditions for conducting experiments. Based on the research results for selected model soils, the dependence of the hydraulic conductivity on the magnitude of the hydraulic gradient was established. The hydraulic conductivity increases with an increase in the hydraulic gradient, and upon exceeding a certain value of the gradient, known as the critical hydraulic gradient, when soil particles attain a stable position, deformation processes practically cease. It was also found that with a gradual reduction in hydraulic gradients, the hydraulic conductivity remains constant within a certain interval. Only after reaching specific gradient values does the hydraulic conductivity start to decrease, but it exceeds the initial values significantly (up to 32%). This indicates that deformations in the soil caused by mechanical suffusion and colmatage are irreversible.