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The use of drainage geocomposites (GCD) coupled with other geosynthetics, has become a common practice in landfill covering and lining systems. The global stability of these systems is closely related to the interface shear strength, which, in turn, is affect by many parameters and testing conditions. Therefore, the evaluation of the interface friction angle is a key issue for the liners design and perfor-mance. One of the laboratory methods used to investigate the geosynthetic interface shear strength is the inclined plane device, very suited for tests at low pressure. The paper deals with the results of an inclined plane test program carried on for two different types of interfaces: GCD – GCL (geosynthetic clay liner) and GCD – GMB (geomembrane). The effects of the dry and the wet conditions, together to the progres-sive damage induced by relative displacement, were investigated. Finally, some considerations regarding the time of loading were also highlighted.