Displacements obtained from pseudostatic slope analysis?

Question

Dear plaxis, 
 When conducting a pseudostatic analysis of a slope, the factor of safety obtained is reasonable, however, the displacements are quite questionable. 
 
 Is it that in slope stability, pseudostatic analysis is used to obtain the FS only, while for displacements a more realistic dynamic analysis has to be conducted?

Stefanos Papavasileiou · Answer

Dear Abdirahman, 
 Force-based pseudo-static methods (as the one implemented into PLAXIS) represents the effect of complex, transient, dynamic effects of earthquake shaking by constants inertial forces, which are incrementally applied to the whole mesh. 
 
 Naturally, this is a crude approach, with the accuracy of the results obtained in the analysis being very dependent on the appropriate selection of the pseudo-static coefficients. 
 
 Due to this, pseudo-static analyses are mostly used to obtain an estimation of the critical acceleration, for which a given structure (e.g. slope, retaining wall, etc.) fails, or to estimate the factor of safety against failure for the design acceleration level. 
 
 Permanent ground displacements are typically estimated by time-domain elastoplastic finite element analysis or sliding block models. 
 
 For further details, please refer, for example, to Kramer (1996): &ldquo;Geotechnical Earthquake Engineering&rdquo;.