Different factors of safety


Hi there,

I have problem with slope stability calculations of tailing dam. I carried out the calculation with the use of different methods and I got the resulting factor of safety as follows:

  • 1.74 for Morgenstern-Price method
  • 1.51 for stress based method
  • 1.4 for strength reduction method

Why theses results are so different from each other? I carried out these calculations following GeoStudio example file where stress correction in the domain is essential. I applied spatial function of ground water conditions.

I attached the model.

If anybody could help, I would be grateful.

Regards Jarek

Best Answer

  • IgnacioEscudero
    IgnacioEscudero Posts: 7 mod
    Answer ✓


    Thank you so much for getting in touch with us, and sorry for the delay in my answer

    It is a big question, because the methods are based on different physics. For example, the limit equilibrium method with Free Body Diagram (sumatory of forces and moment of force)  it does not include a constitutive stress-strain law and therefore, does not address displacements or strains within the domain. The results from limit equilibrium and finite element stability analyses are reasonably close if the normal stress distribution along the slip surface is primarily related to the overburden stress, as is the case for relatively flat, natural slopes. Greater differences arise when shear stress concentrations are present, as observed at the slope toe (due to the slope steepness). On the other hand, when we do a comparison of the FE and LE Stability with SRS techniques reveal that a key advantage of the SRS technique is that the mode of failure evolves naturally as the strength is reduced. 

    For send and upload the project to our Engineering Team here is the email: support@geoslope.com.

    They would give feedback about what is going on with the project.

    Let us know if we could support you with anything else!

    Kind regards


  • JarosławCzarzasty

    Thank you Ignacio for the answer.

    Is it possible to judge, which of these methods is the most reliable and which is the least reliable in my case?

    best regards


  • JarosławCzarzasty

    My other concern is that the difference of FoS between these 3 methods (LE, FE and SR method) is too big. If you look at the example provided by Geostudio_learning\Example_file "Strength reduction stability", you will notice that the FoS is between 1.4 and 1.5. In my case it is between 1.4 and 1.74.

    Maybe the problem is with the complexity of my model and the Geostudio engine which can not cope with such complex models?