Abstract: The large direct shear tests on interfaces of geomembranes/geocomposite and geotextile /geocomposite are described. It is found that the presence of drainage nets has an important effect on the shear strength of interfaces with geocomposite. When the normal stress is larger than 210 kPa, the drainage nets severely damage the rough surface of coextruded geomembrane, resulting in a reduction of shear strength parameters, i.e., the peak friction angle decreases from 17.4° to 8.6°. However, on the geotextile/geocomposite interface, when the normal stress is larger than 50 kPa, the embedment of drainage nets increases the plowing effect, resulting in an increase of shear strength parameters, i.e., the peak friction angle increases from 10.6° to 21.3°.