engleski

Problems of Hydraulic Conductivity Estimation in Clayey Karst Soils

Even in karst areas, considerably thick soils can be found in accumulation zones. Here, the degree of groundwater vulnerability depends not only on the thickness, but also on the hydraulic conductivity and retention properties of the soil cover. The hydraulic conductivity of fine-grained karst soils from Slovakia, Croatia and Austria was studied within several international research projects, by the application of four different test methods. Results are discussed from different points of view. Triaxial tests yielded a very broad interval between the maximum and minimum hydraulic conductivity (from 5.83x10-7 ms-1 to 3., 50x10-11 ms-1), therefore the mean value cannot be used in any calculations. The consolidometer method gave lower values in general, between 9.40x10-10 ms-1 to 3.59x10-8 ms-1. However, this method overestimates the soil &#8220; impermeability&#8221; . Eestimates based on grain size are unsuitable, as fine-grained soils did not fulfil the random conditions of known formula. Finally, the &#8220; in situ&#8221; hydraulic conductivity was measured using a Guelph permeameter. As expected, &#8220; in situ&#8221; tests showed 100 to 1000-times higher kf than the laboratory tests. This method best reflects the real conditions. Therefore, only this type of data should be considered in any environmental modelling. In a soil profile, hydraulic conductivity depends on the mineral composition, depth, secondary compaction, etc. The degree and duration of saturation with water is very important for young soils containing smectite. Their hydraulic conductivity might be very low when saturated for long time, but also very high, when open desiccation cracks occur. A very slight trend was found, but only in Slovak soils, showing a decrease in the hydraulic conductivity with increasing content of the clay fraction <0.002 mm. These results should contribute to a better estimate of the protective role of soils in groundwater vulnerability maps.

karst soils; hydraulic conductivity; triaxial permeameter; consolidometer; guelp permeameter; grain size

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