Displacements and Safety Factor

Question

I have an appointment, I am evaluating a dam, my question is: can I know the displacements that happen when reaching the minimum safety factor, because the scale of values that appears in the Safety legend does not have a physical meaning.

Stefanos Papavasileiou · Answer

Dear Juan, 
 When running a safety analysis, a non-physical reduction of strength is induced to the material parameters. This, as you mention, develops unrealistic deformations, which makes it difficult to extract any displacements at a specific Factor of Safety (FoS). 
 Typically we mention that when reaching the FoS value (or &Sigma;&Mu;sf) at the critical state (failure), an indication of the deformations can be seen at the start of failure. However, this is not absolutely realistic as again the calculation process does not reflect a physical process. The goal of the safety analysis is to identify the failure mechanism by artificially reducing materials' strength. 
 As in many cases in geotechnical engineering, the user's judgement as an engineer is required here, too.

Stefanos Papavasileiou · Answer

Dear Juan, 
 A similar question has been asked before in our forum. You can find it here: https://communities.bentley.com/products/geotech-analysis/f/plaxis-soilvision-forum/195789/displacements-obtained-from-pseudostatic-slope-analysis/581864#581864 
 As a side note, in case you have not discovered it we have a detailed article with examples here: https://communities.bentley.com/products/geotech-analysis/w/plaxis-soilvision-wiki/48472/fundamentals-of-pseudo-static-analysis-in-plaxis