i did the automatic calibration for the Dobrany and Motol sand and tried to model the soil tests also in Plaxis and then to compare both. For the triaxial test the ExCalibre curve and PLaxis curve are narly the same but for the Oedometer curve there are always big differences.
So my first question is, if anyone of you knows, why there is that difference between ExCalibre and Plaxis for the Oedometer curve?
And the second question is, if anyone knows, if the results (strains) of the Plaxis soil test tool are engineering or true strains?
Attached you can find two figures (two materials), where the difference can be seen very well.
Thanks in advance and kind regards
Hi Marco, this seems as zero-stress problem to me. Oedometric tests are in Plaxis SoilTest run from 0 stress, which is virtually undefined in hypoplasticity unless you set “pt” value – artificial stress, which makes true 0 stress to be non-zero for the model. Contrary, ExCalibre, when running oedometric test, starts from the stress of the first loading step, which is different from 0. It is actually hard to compare the two, as in ExCalibre you cannot set pt. If you really need to have good comparison, you can include artificial almost-zero calibration point in ExCalibre input file, and add almost-zero but nonzero pt value in Plaxis. Then the curves should be similar.
In any case, I suggest you should evaluate the models using other element test drivers, such as triax or idriver available at soilmodels. Regards David
Thank you David, it seems to be clear now.
How does the initial void ratio taken into account in Plaxis when using Hardening Soil model, and how do you plot the void ratio versus stress curve in Plaxis?