Determination of direct slide coefficient and interfacial frictional resistance at the contact between the fill material and geosynthetic was the purpose of the paper. The fill material was an ash-slag mixture from Skawina Power Plant and from the settler of ArcelorMittal Poland Steel Plant in Kraków Płaszów. The shear strength and interfacial frictional resistance tests were carried out in the direct shear box apparatus at the moisture content close to optimal at the compaction indexes 0.90, 0.95 and 1.00. Test results revealed that the shear strength parameters of the analyzed ash-slag were high. The parameters describing the frictional resistance at the contact: ash-slag – geosynthetics were also high, which allowed obtaining high values of the direct slide coefficient as well as the coefficient of interfacial friction.

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