Determination of Dispersive Erosion Resistance in Fine-Grained Soils with Newly Developed Test Equipment

Dispersive soils cause great damage to hydrophilic earth structures and unprotected slope surfaces because of their high erosion sensitivity. In fine-grained soils, erosion resistance decreases with increased dispersibility. The dispersion mechanism of clays is controlled by the clay mineralogy and by the physicochemical repulsive forces in the clay–water system. The erosion resistance of dispersive soils can be determined by surface and internal erosion tests. In this study, the internal erosion resistance of soils was determined by using new test equipment that allowed the flow to pass through a hole when the dispersion mechanism in fine-grained soils was activated. The experiments for this study were performed under a single hydraulic head on two different natural dispersive soils with similar clay mineralogy. In this experimental system, both uniform and fully developed flow conditions were achieved. Time-dependent flow rates obtained from the experimental system can be used to determine hydraulic parameters, such as energy grade line, at very low error rates with the help of basic theorems of pipe hydraulics in theoretical hydraulic models, which were formed using a physical hydraulic model. Moreover, the erosion rates were quantitatively determined by using the continuity equation, and critical shear stresses were qualitatively compared for internal erosion developed by the dispersion mechanism. The sand/clay ratio determined the erosion resistance and behavior of the dispersive soils.