It is measured in large direct shear boxes under a range of normal stresses, giving peak and large-displacement friction angles and adhesion for each interface. A lined slope is only as stable as its weakest interface, often smooth geomembrane against geotextile or the inside of a hydrated GCL. Designers call for project-specific tests with the actual materials, because published values vary widely.
Interface friction between smooth sheet and the geocomposite is the weak link, so the slope only works textured on both sides.
Test interfaces with the actual rolls and soils going in the ground; a material swap during construction can quietly invalidate the slope design.
Also heard as
- interface shear strength
- interface friction angle
Related terms
Textured geomembrane
Geomembrane with a roughened surface that raises friction against soil and other geosynthetics on slopes.
Asperity height
Height of the raised texture on a textured geomembrane, measured from the core of the sheet.
GCL
Geosynthetic clay liner: a factory-made barrier of sodium bentonite held between two geotextiles.
Geomembrane
Low-permeability polymer sheet used as a liquid or gas barrier in liners, covers, ponds and tunnels.