From the GMA Techline
Do you have a recommendation for what Factor of Safety to apply to the allowable geomembrane force for anchor trench calculations?
(Melanie | Colorado)
Reply: Over the years my thoughts have changed from having a high FS for geomembranes in their anchor trenches to treating the situation very differently. The motivation being that I would generally rather have the GM slide out of the anchor trench in the case of high tensile forces than resist them only to have the GM tear somewhere down the slope (it being covered or uncovered). If seismicity is involved, this is certainly the case.
My approach now is to calculate the total force available from the anchor trench’s resistance to the ultimate strength of the geomembrane. This way an anchor trench ratio can be calculated. By varying the anchor trench’s resistance (its runout or depth) you can favor either pullout or tearing.
I think this is the correct approach to your question and the underlying issue.