Hello,
I have two questions about the time dependent analyses in Plaxis
1. There is an option in "plastic" analyses to enter the time. But it also says it does not consider the soil consolidation. So what is this time input for? how is it being considered in the analyses?
2. For calculating the consolidation, can the "HS Small" model be used?
Cheers,
Farbod
Hi Farbod,Indeed a plastic calculation does not take time effects into account. But there are two exceptions: one is when we use the Soft Soil Creep model, and the other is when we use the viscoelastic behaviour for geogrids. For the latter case, you can also check November's coffee corner on the "mechanical behaviour of geosynthetics". You can find it here: event.on24.com/.../45EA334E1B5491C616B6374F8B81C028For your second question, the answer is yes. You can use the "HS Small" model for consolidation calculations.
Hello Vasileios,
I appreciate your answer it helped me better understand how plastic analysis works. However, I would like to verify something, I found a consolidation analysis with the Creep-Clay-1S constitutive model, but this was carried out with a plastic analysis type calculation plus a time to take into account the growth of the leaves, in this my case the question is if:-This analysis will only take into account creep consolidation, and not elastic, primary and second consolidation, right?-Is this correct or should I always do a consolidation analysis with the consolidation calculation type?
Dear Edwin,
You're making the story a bit confusing by mixing concepts. So to clarify:
1) When doing "Plastic" analysis type one is NOT doing consolidation. Hence, the statement "I found a consolidation analysis carried out with a plastic analysis type" is contradictive and incorrect.
2) There is no such thing as elastic, primary and secondary consolidation. There is "consolidation" (aka primary compression), which is the time dependent generation of settlements due to dissipation of excess pore pressure and there is "creep" (aka secondary compression), which is the time dependent generation of settlements due to densification of the soil particle matrix. Those two are independent phenomena.
3) PLAXIS can calculate the effects of consolidation by doing either a "Consolidation" or "Fully coupled flow-deformation" analysis type for any constitutive soil model.4) PLAXIS can calculate the effects of creep in any calculation analysis type under the condition that both: - one uses a constitutive model that can calculate creep. For instance Soft Soil Creep, Sekiguchi-Ohta Viscid, Creep-SCLAY1S. - one specify a time interval for the calculation phaseWith kind regards
Dennis Waterman
Thanks Denis for replying to Edwin. However, I am still quite confused about two things:
1. You mentioned in your firs point: "when you do plastic analyses, you do not consider consolidation". If thats true, then what is the SSC model calculating when you do plastic analyses? Is it only elastic deformation (i.e. time does NOT matter)?
2. What ACTUAL difference does it make when you set your material to undrained compared to drained in the SSC model? because the parameters do not change when you do so. Because according to the link below, it makes absolutely no difference right?
communities.bentley.com/.../after-a-consolidation-analysis-i-have-excess-pore-pressures-in-drained-material-sets-why
Thanks a lot in advance
Dear Farbod,
1) In a plastic analysis (or any other analysis) when time is specified the SSC will experience creep. Creep and consolidation are separate independent phenomena. Hence, time does matter.
2) If the material is drained no excess pore pressures will be generated, and if the material is undrained than excess pore pressures will be generated. Note that the setting drained / undrained is only used in a Plastic, Dynamics and Safety analysis. A Consolidation, Fully-coupled flow deformation and Dynamics with consolidation analysis will use the real permeabilities to simultaneously develop and dissipate excess pore pressures. With kind regards,