Schmertmann vs. Plaxis
Schmertmann vs. Plaxis
(OP)
I am sure that some of you made this comparison.
When I calculate with Schmertmann, due to theory, calculations ends 2B below the foundation. When I model the same foundation in Plaxis, it is clear that there is settlement below 2B.
Do you really think there will be no settlement below 2B? What is your experience about this comparison? Do you know any resource, paper?
Regards,
b.
When I calculate with Schmertmann, due to theory, calculations ends 2B below the foundation. When I model the same foundation in Plaxis, it is clear that there is settlement below 2B.
Do you really think there will be no settlement below 2B? What is your experience about this comparison? Do you know any resource, paper?
Regards,
b.





RE: Schmertmann vs. Plaxis
RE: Schmertmann vs. Plaxis
I know that Plaxis does not follow this rule. Actually Plaxis and other finite element softwares do not follow any rules that are based on empirical or numerical approach. They are following the finite element concept. And I don't know your opinion, but I am a fan of finite element. So, I am trying to understand the reason of difference.
RE: Schmertmann vs. Plaxis
Don't let the "accuracy" of the finite element approach mislead you to think that it's "accuracy" is also correct.
I go back to an old saying that certainly applies to geotechnical engineering and much of engineering in general.....
We are guilty of measuring with a micrometer, marking with a crayon, and cutting with an axe.
RE: Schmertmann vs. Plaxis
So, to come to the reality, thus would you guys limit the depth of the model to 2B -for square footing- so we do not see any more settlement below that? Of course, the settlement over 2B would be relatively large compared to Schmertmann but it may be a useful assumption.
RE: Schmertmann vs. Plaxis
RE: Schmertmann vs. Plaxis
Plaxis and other FE programmes can be a wonderful tool - but it is a tool and is not "exact". I've attended conferences in Singapore where papers have put forth very interesting Plaxis analyses - 3D and all that - all based on E being derived from an SPT N value (uncorrected or not - no one specifies). Therein lies the rub, if I may. Determining the "real" values of E or other parameters for the FEM are very difficult. In the analyses, changing E by 10% can change your result by 10%. If you can't get the "real" value of E, then your result is a wonderful indication of the behaviour - but not of the reality. I've pointed out in other threads that settlement computations cannot be taken as "exact" - try four or five different computational methods for settlements in sand and see what range of answers you obtain. This is why geotechnical computations are fraught with vagueness/fuzziness - our COV values are in the order of 25 to 50% whereas steel and concrete at in the range of 5%. And getting back to Singapore, I asked if anyone, based on the "real" measurements of excavation support movement tried to back-calculate the E values and then to their N values so they can get better fits . . . the response was "No. Don't have the time."
Enjoy having you on the site - regards and