Hi Prof. David,
I have obtained these results in that attached picture using Triax and got confused when seeing that an isotopically normally consolidated sample does not follow a trend that looks similar to the traditional Roscoe Surface. Have I done something wrong or this is what is expected from your hypoplastic model?
Thank you,
Hashmi
Undrained Tests with Basic Clay Hypoplasticity
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Dear Hashmi, this is correct response of the model. Actually, the observed shape of stress path is due to response envelopes being translated elipses in the stress space. The normally consolidated sample response can be corrected by either using intergranular strain concept, or by socalled Ddependent L approach. It is discussed thoroughly in this reference: Mašín, D. and Herle, I. (2007). Improvement of a hypoplastic model to predict clay behaviour under undrained conditions. Acta Geotechnica 2, No. 4, 261268. Regards David
ok, thank you David.
Can you please provide a clarification on the following:
In triax program, the following are the inputs when using hypo_clay with istrain:
fi cr, lambda, kappa, N, r, R, mr, mt, betar, chi, e0
however, when referring to your notes, it says that for hypo_clay mR is replaced by Ag and ng while mT is supplemented by mrat instead. Therefore, how can i make triax recognise these input parameters: Ag, ng and mrat?
Correct, this is because hypo_clay is 2005 version of clay model. To use the most recent clay version, use hypo_clay_anisot and set anisotropy factor alpha_G = 1. Regards David
ok thank you. is there an updated pdf manual that includes the newer versions of hypo_clay models in triax that came after 2005?
I am currently using hypoplasti_clay_anisot_istrain, can you please confirm that the parameter nu is poisson’s ratio?
Hi David,
Can you please clarify the following parameters in Triax:
hypoplasti_clay_anisot_istrain: fi cr, lambda, kappa, N, nu, alpha, R, betar, chi, G0, n, mtrat, inic. his. var.: e0, istrain, pt
1. what is G0? confused that it could mean Ag or is it just initial shear stiffness?
2. is the n the same as ng?
3. what to insert for istrain and pt after e0? (i initially left them blank)
Thanks!
Hi Hashmi, G0=Ag, n=ng,
for istrain you should put all 9 components of complete intergranular strain tensor (rowbyrow) with x being vertical coordinate, that is [isxx, isxy, isxz, isyx, isyy…]. For initial state, you probably want to set nine zeros.
for element test simulations, you will probably use pt=0, as you will not need to cope with nearzero stress problems occuring often in FE simulations. pt is arbitrary (you can leave it blank), but at least nine zeros for istrain (or your values if you know what you are doing) are important.