Hello,

I am using clay hypoplastic umat code and trying to verify the code with the simulation on the paper of Prof. Masin. I found in the paper (Masin, 2005, A hypoplastic constitutive model for clays) there is no details of boundary conditions of the simulation but stress path. As shown in the picture, the p and q are not straight line and also be normalized by pe^asterisk which varies with void ratio. The paper describes the three experiments which are also simulated by clay hypoplasticity as follows:

PhM19: shear test with constant mean pressure on K0 overconsolidated specimen.
PhM21: undrained compression test on a nearly normally compressed specimen.
PhM17: constant p0 extension test on a K0 overconsolidated specimen

I am a little bit confused about these description — for PhM19, what is constant mean pressure? Is that mean we need to change both horizontal pressure and vertical pressure at the same time in the triaxial shear test simulation to make the mean pressure constant? And which parameter will be changed by switching overconsolidated specimen to normally compressed specimen? If the OCR of normally compressed specimen is 1, what is the OCR for K0 overconsolidated specimen?

I am not sure if this is a common questions or it is because my shortage of background. I appreciate your response!

Thank you!

Shen Wang

1. Gertraud Medicus 2 years ago

Hi

2. Gertraud Medicus 2 years ago

Hi Shen,

yes: the test with constant mean pressure implies that p’ is constant and that means to change both: sig_axial and sig_radial. E.g. for triaxial compression: increase in sig_axial and decrease of sig_radial by keeping p’ const.

Related to normally consolidated (isotropic normally consolidated states): you don’t have to change parameters, but adjust the void ratio e, that e_initial is on the NCL. for isotropic normally consolidated states the OCR is pe/p=1.

Related to K0 oedometric normal consolidated states: Equations (22)-(25) (Mašín, 2013) will help to get the oedometric normally consolidated p/pe. the mobilized friction angle at oedometric normally consolidated states follows from Jaky’s relation for K0. for oedometric normally consolidated states the OCR=pe/p is larger 1. (and smaller 2)

Clay hypoplasticity with explicitly defined asymptotic states, Acta Geotechnica.

If you only need the initial void ratios for element test simulations, you can certainly also take the initial void ratios of the experiments PhM17/19/21 which I think should be in here:

I hope that helps.
Regards, Gertraud

• Shen Wang 2 years ago

Hi Gertraud,

Thank you so much for the detailed explanation and the link! They do help!

Best regards,

• David Mašín 2 years ago

Gertraud, thanks for your replies to Shen Wang. Regards David