The environmental performance of waste disposal facilities lies in the correct design and construction of their liners. There are several liners design recommendations prepared by regulation agencies. Typical liner design includes single liners and composite liners. Common single liners are constructed by a single layer of low hydraulic conductivity compacted soils with final thickness in agreement with the applicable regulation. Composite liners include in their design combination of compacted soil layers and inclusion of geosynthetic layers with different function. Most common composite layer is built by a compacted soil layer and a geomembrane. Hydraulic performance of liners lies on their hydraulic conductivity and the amount of leakage due to geomembrane imperfections while mechanical performance depends on soil internal friction angle and soil – geosynthetic interface strength. Liner stability against sliding is of uttermost importance in side slope liners. In this research the effect of the compressibility properties of compacted silty soils are studied. Results of oedometer tests, direct simple shear tests and consolidated – undrained triaxial tests are analyzed. Shear strength parameters are studied in two different moisture conditions: specimens at compaction moisture and saturated specimens. Alos effects of shearing velocity in interface strength are also studied by mean of direct shear tests between soil samples and a smooth geomembrane.