Slope Stability Equilibrium and Stress states with ABAQUS

[MCC1966]

I am wondering if any of you has conducted slope stability analysis with ABAQUS.
Finite element is powerfull tool for observing Slope stability behavior with time. The Maximum contour of Mises Stress can be considered as mark of the slip surface location while FOS is computed by a criterion established by the analyst.
Ideally the slope is a geo-system subject only to gravity force. However, if one uses Geostatic step during which the gravity load must be applied then one will get zero stress case.
Your detailed comment is very valuable in this regard.

 

[hamadadf]

i'm modelling excavations and yea i check slope stability. but i am not sure i understand your question

 

[MCC1966]

Sorry Hamadadf for the late answer
I meant that if one has a slope then one will not be able to get any Idea (outputs) about its equilibrium or stability status (due to is gravity and currect pore water conditions within it) unless there is change in the BC. As, according to ABAQUS, the slope before being subject to load or BCs changes (a system subject to its gravity before the change in BCs) must be analyzed under Geostatic step which results in that the slope is Stable.
Then if one has a slope, then how one knows about its Equlibrium and Stability status
I hope That my clarification is good now

 

[hamadadf]

Thats correct, but as far as i understand even geostatic step is an equilibrium step, so if the slope is not unstable, the geostatic step should not converge.
did you try 90o slope at geostatic step and the step converged?

 

[MCC1966]

In your reply: do you want to say if the slope is not unstable or stable
What do you mean by try 90o slope.
In Geostatic step, after you describe the External Force(gravity in this case) and Initial Stress (in the Edit Keywords). By choosing to work with Geostatic Step you are asking ABAQUS : Make sure from that External Load is in Equilibrium with the Initial Stresses I have given you, Otherwise modify my given Initial Stresses to Equilibrate the External Force described. ABAQUS will not do that if the Initial Stress described are unrealistic and will diverge in this case

 

[hamadadf]

sorry i meant unstable.
ok..if that is how analysis goes.. what i do actually in my analysis is that
step 1 (geostatic)
i model the whole soil unexcavated
step 2 (soil or static analysis)
i excavate whatever slope is want. and check stability
why don't you try it this way?

 

[MCC1966]

Thanks hamadadf
Although it requires some efforts It seems an interesting way to deal with Stability analysis of Slope through ABAQUS .
You meant that if I want to analyze my NATURAL slope I assume that there no slope at the beginning (level ground) : Geostatic Step. Then I cut /remove elements (in one shot) of the soil (based on the angle of my natural slope): SOILS Step.
I have to think about the implication of this way on changing the problem that was otherwise Natural Slope.
Do you know if this approach has been tried before in ABAQUS, please refer me to some sources
Thanks

 

[hamadadf]

I don't know if this approach was used before in abaqus. as i mentioned to you my problem is excavation in flat soil. but i assume if your use of geostatic step was not working right and it doesn't give you any variation of stresses, then you can model it this way. you can even consolidate the soil in the next step for long time to be sure all excess pore pressure dissipated and soil reached its final settelment.