Q: Is there a minimum ply-adhesion value for a triplanar geocomposite? I ask this knowing that GRI-GN4 (Test Methods, Required Properties and Testing Frequency for Biplanar Geonets and Biplanar Geonet Composites) specification states a minimum of 1.0 pound/inch.
A: Yes, the minimum ply-adhesion value of 1.0 ppi is a pretty good number for triplanar and biplanar geocomposites. Please see the attached figure at right of shear strength versus peel strength, which confirms this opinion. The figure is from years of data collected by the Geosynthetic Institute (GSI) at various sites with many different products.
That written, this is certainly not the whole answer, particularly if you are designing on the West Coast in the U.S. If seismic issues exist with steep slope, please consult R. Thiel’s 2023 keynote address from the 12th ICG in Rome, Italy, for a more complete answer:
Thiel, R. (2013). “Selection of long-term shear strength parameters for geosynthetic interfaces.” Proc., 12th International Conf. on Geosynthetics, Rome, Italy, www.12icg-roma.org.