ASD in soil nailing stability with SLOPE/W

[pileexpert]

Hi dears,
I had a discussion with an geotechnical expert on the parameters should we comsider for slope stability based on FHWA report NO.017
in this report it says we should consider global FOS=1.5 and also we should (as i understand) use FOS=1.8 for reinforcement and FOS=2 for bond strength, now the question:
is it logical to apply these FOSs to get 1.35 or no. since we are using ASD method we should use ultimate loads?

 

[Doctormo]

I believe the factors you list are for global stability, reinforcement tension, and reinforcement pullout (bond strength) which are independently checked. Tension and pullout are internal stability checks whereas global stability is an external check. Like resistance factors, there can be different factors of safety for different items.

The global analysis when done properly will also consider tensile strength and pullout when failure planes intersect the reinforcement but these would be unfactored (no FS) resistances as the global exercise is to calculate an overall factor of safety for that failure mode. Application of duplicate factor of safety's just yields excessively conservative results if I understand your question.