TEXTILES.ORG
From the GMA Techline
Subject: Shear strength — We are looking for interface shear strengths of a geocomposite- to-geocomposite interface. Both composites would have nonwoven fabric. Is test data available that indicates what this interface strength would be? (Chet, Ohio)
Reply: The shear strength of the 2 nonwovens against one another is in the neighborhood of 20-30° depending on the normal stress applied.
These same fabrics on geonets, in the form of a geocomposite, are another story. The underlying ribs of the geonets will result in a stick-slip mechanism during shearing displacement, whereby the response will be quite irregular.
You should really commission a few tests, where the applied normal stress is critical.