how to get factor of safety of slope based on finite element analysis 9

[ananan88]

Dear friends:
I'm using some finite element softwares such as ADINA\ANSYS to analysis the stability of a slope. Although I can calculate the stress and strain of each elements,I don't know how to calculate the whole safety factor of a slope.Do I need to draw many slip surfaces and calculate each of the safety factors and then find the mininum value?How to programming it?
Thank you for your help!

 

[kwalton]

That will depend on the software. I have been using Phase2 (Rocscience) and my version does not do SRF automatically. I have to work out c & phi for each run then change the Mohr Coulomb parameters each time. I understand that the next version of the software will incorporate automatic generation of SRF parameters. Other software may already include this facility. (Don't forget to divide tan phi by FOS then take tan-1)

 

[gamadot]

I agree with great suggestions from kwalton. I have few misconceptions about shear strength reduction(SSR) technique.I hope that a clarification can be found at this site.For starting an analysis with SSR we need to know some value of c and phi and we keep reducing these two values by a same factor until non convergenec is achieved.So the final c and phi value depends upon the start value.In my case i have a bunch of experimental values of c and phi obtained from undisturbed, remoulded and direct shear and triaxial shear test which were used as a starting value in SSR.Since the experimental values are widely varying and hence the final values from SSR are. Can anyone tell me which value to be considered as the strength parameters prevailing at the time of slope failure.

 

[kwalton]

To gamadot:

The problem is just the same whether you are undertaking Finite Element or Limit Equilibrium analysis. You have to decide on realistic strength & density parameters to start with and go with those unless you are undertaking probability analysis. You need to consider the nature of the material, likely failure mode and the spread of parameters obtained from the varying test methods. You probably have too much information! Professor Jennings from Witwatersrand in South Africa once said to me when we were doing some large scale plate loading tests "Only do one test then you only have one answer". He was saying it "tongue in cheek" but it does acknowledge the difficulty of deciding on appropriate parameters.

 

[Rocscience]

Phase2 version 6 by Rocscience offers fully automated finite element slope stability analysis, using the SSR (shear strength reduction) method. With one mouse click you can determine the critical strength reduction factor (safety factor) of a slope. The SSR analysis in Phase2 can be used with Mohr-Coulomb or non-linear Hoek-Brown materials, and can be applied to soil or rock slopes.

The validity of the SSR results produced by Phase2 has been well documented. The SSR method produces results which are identical or very comparable to limit equilibrium slope stability results. Over 30 verification examples are documented in the Phase2 SSR Verification Manual. Models can be easily built in Phase2 or imported from Slide (limit equilibrium slope stability program).

For more information see

http://www.rocscience.com.