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[Luc Scholtès <question694100@xxxxxxxxxxxxxxxxxxxxx>]

Question #694100 on Yade changed:
https://answers.launchpad.net/yade/+question/694100

    Status: Open => Answered

Luc Scholtès proposed the following answer:
OK... I am still confused because you say that you chose the parameters
that matches your soil but then you say that there is a discrepancy when
you compare the stress strain curves...

If I understand correctly, your real soil has an internal friction angle
of 38°. To obtain this value, you performed several direct shear tests
at different normal stresses and then, based on the Mohr-Coulomb
criterion, you used a linear regression to fit your data (peak or
residual shear stresses and associated normal stresses).

My question is: what is the internal/emergent/macroscopic friction angle
of your DEM model/numerical material?

I see that you defined a 40° in the following lines of your script:

# friction angles
compFRIC=15. # during compaction (controls porosity)
FRIC=40. # during shear

These lines defines the interparticle friction angle, the value that is
used in CohFrictMat.

This value (40°) does not define the internal/emergent/macroscopic
friction angle of your DEM model/material.

To estimate the internal/emergent/macroscopic friction angle of your DEM
model/material, you need to do exactly what you have done with your
soil: for a given value of the interparticle friction angle, perform 2
(at least) simulations with different normal stresses and then fit the
results with the MC criterion. You will see that there is no direct
correspondence between the interparticle friction angle defined in
CohFrictMat anf the internal/emergent/macroscopic friction angle of the
DEM material/material.

The calibration consists in adjusting the interparticle friction angle
(the one in CohFrictMat) that produces an internal/emergent/macroscopic
friction angle of 40°.

Sorry if all this was clear but, again, I want to make sure to
understand the source of your issue.

Finally, you may want to have a look at this article: https://hal.univ-
grenoble-alpes.fr/hal-01951842/document

Luc

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