Pore Pressure Generation in Axisymmetry Model

FLAC2D
1

Is it possible to generate pore pressures in an axisymmetric model? I am running an undrained triaxial test code, and I am unable to generate pore pressures in the model if the command “model configure axisymmetry” is enabled.

1 Like
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Hi Cristian,

Axisymmetry logic is not yet complete in FLAC2D, and we will be working on enabling it for fluid, thermal and dynamic calculations in future updates/releases. How do you generate pore pressure in your model? If it is through the fluid module, this currently won’t work.

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This is interesting @apyatigorets I did not know this about the axisymmetry logic. Worrying.

However, @CrissBidermann, I can simulate undrained triaxials with pore pressure generation fine using for instance the NorSand model in axissymmetry using a high fluid modulus in FLAC2D.

e.g. zone gridpoint initialize fluid-modulus 2.0e9 ; Pa

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@paul, sorry for a delayed response on this. I believe axisymmetry should work fine with mechanical pore pressure generation. However, transient fluid logic has not been specifically adjusted to the case of axisymmetry in FLAC2D 9 (or later). We plan to work on this in near future (as well as other remaining item for axisymmetry).

In the meantime, would you mind sharing your example where you use axisymmetry with PP (or maybe some simplified version)? You can send it directly to me apyatigorets@oneitasca.com. It would be good for us to use it for testing purpoces.

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Will do @apyatigorets.

I see it has now been made explicit in v9.2.21 with the error:

“*** Axisymmetry logic is currently limited to standard mechanical analysis. Dynamic, fluid, or thermal processes cannot be active with axisymmetry.”

I used to use dynamic with axisymmetry to simulate triaxial tests, but only to control load application rate and determine the critical timestep. It still works with just cycles or steps at least.

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@paul we have recently restarted work on axisymmetry, and for now looking into dynamics. Overall, all the logic is there for this module, it just hasn’t been thoroughly tested. That is why we added dynamics in the error message. However, for fluid and thermal modules we expect that some changes will be needed.