Identification And Treatment Of Erodible Clays In Dikes

When it comes to flood protection, the established method is to use impermeable material in dikes, to prevent seepage. This material is usually some kind of clay soil which is considered as impermeable and erosion-resistant. Dispite that, in many occasions not only seepage, but the failure of the dam occured due to surface erosion, because these kinds of irregular soils are barely investigated, and their presence are not considered during the phase of designing.In geotechnics these soils are called dispersive clays, and their greatest hazard is that they are not distinguishable at sight or by the standard geotechnical tests from the regular erosion-resistant clays, therfore many dams are built by these kind of materials, causing extra risk when it comes to evaluating the probability of failure. The reason for this kind of behavior can be found in the structure and the distribution of the clay minerals which are building up the soil.Based on earlier experiences and papers it is possible to reduce the magnitude of erosion by mixing the soil with slaked lime. First to evince the dispersive nature of the soils we developed a testing program. Therefore we collected samlpes from the Great Hungarian Plane, and identified them by the pinhole test after Sherard. If the soil was identified as a dispersive clay, slaked lime was mixed to it, and the test was performed again to see if the soil became less dispersive, therefore more erosion-resistant or not. The main goal was to find an optimal value of the added lime.The main chapters the paper present the background of the dispersive soils, and the mechanism of failure, the tunnel erosion. Shortly the laboratory testing methods are demonstrated, and the way feedback affects the further tests, and the results of the treatments, the changes of the degree of dispersion are shown.