Safety Factors

Question

Hi all, 
 Can anyone give some advice about unstable situations due to soil collapse. I mean, can anyone recommend a way to calculate safety factors (<1.0) if you got a collapse in plastic phase using only plaxis results (without a limit equilibrium model)? 
 Thanks in advance! 
 Francesc

Martin Hawkes · Accepted Answer

I'm not a member of the Plaxis staff. But I have a question about Jamal's suggestion. If you limit the MPhase to something like 0.5, then at the end of that phase you would only have about 1/2 of the condition that you're trying to model. In the example in the pdf this would be 1/2 of the mobilization of shear stresses to account for the non-horizontal ground. Now if you follow this condition with a FOS phase which starts reducing the shear strength of the soil,and trying to compute equilibrium (for the partially complete prior phase), I'm not sure of how to interpret the meaning of the computed FOS. 
 I my opinion (and I could be wrong about this) you can't calculate a valid FOS less than 1.0 using methods based on equilibrium, and Plaxis is great at calculating equilibrium. I'd recommend starting from equilibrium, say by removing the surcharge and then increase the surcharge to get failure. 
 Martin

Safety Factors <1.0

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