Geotechnical research of mottled clay shales originated from Szymbark near Gorlice are presented in the paper. Grain-size distribution, Atterberg’s limits, compactibility parameters, permeability coefficient, swelling index and shear strength were determined. The test results revealed that mottled clay shales has good compactibility and low permeability. According to grain-size distribution and Atterberg’s limits the shales were classified as a normal active clays. Swelling index of tested soil were in range of 8–15%, what means that the soil is semi-expansive stratum. Shear strength tests revealed that at the optimum moisture content mottled clay shales have high values of angle of internal friction and cohesion. At low moisture content shales have very high shear strength parameters, which are very similar to parameters of flysch rock masses published in literature. Therefore, at the moisture content higher than optimum, which corresponds to soft consistency, the shear strength of mottled clay shales decrease significantly and the values of shear strength parameters are similar to clayey soils.

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