<p>This paper studies the impact of liquid on the landfill bottom liner interface strengths and slope stability. A series of laboratory direct and ring tests were performed on soaked and submerged geosynthetic interfaces to investigate the impact of liquid on bottom liner interface strengths. The large direct shear tests performed on dry and soaked specimens yielded similar peak and large displacement (LD) interface strengths. The torsional ring shear tests were performed on submerged specimens and yielded a lower peak interface strength than those performed on dry specimens, which revealed liquid reduced the Velcro effect between a nonwoven geotextile and textured geomembrane. However, The LD and residual shear strength obtained from the ring shear test were found to be the same for dry and submerged specimens. The paper also introduces a method to calculate the pressure head within a landfill leachate detection zone for use in slope stability analyses that use soaked or submerged interface test results.</p>