Hi Hansini

I have not worked on UMAT, but have worked on void ratio dependent permeability (in input file). I will try to answer your question if you can clarify the following line.

What do you mean by "Although ABAQUS allows the permeability to be defined as a tabular function of void ratio it is not the same void ratio I have defined in my UMAT".

Hi Sridhar,

Thanks for your helping hand.

I define void ratio as a state variable in my UMAT (for constitutive equations)

But ABAQUS has void ratio as an inbuilt variable which is used for consolidation equations. These two are little different.So I want to make permeability as a function of state variable.

Hi Hansini

Void ratio is a state variable in ABAQUS as you mentioned. But as per my understanding, we will be required to define the initial void ratio as shown below. Also, if you define void ratio dependent permeability as shown below, the ABAQUS will take the respective permeability value when the corresponding void ratio is attained in the model. Hope this helps.

To define constant permeability.

*Permeability, specific=10.

2.9e-09,

*INITIAL CONDITION, TYPE=RATIO

NALLclay, 1.2965, 0., 1.2987, 0.04

To define variable permeability.

*Permeability, specific=10.

0.24e-06, 1.6320

0.38e-06, 1.8059

0.47e-06, 1.9122

0.58e-06, 2.0433

0.75e-06, 2.2454

*INITIAL CONDITION, TYPE=RATIO

clay, 2.2519, 0., 2.2519, .23

Hi Sridhar,

Thank you very much. I implemented what you had suggested. I could not observe much change. Could I ask how you define your void ratio.and why it is greater than 1. Since I am working with sand, void ratio is between 0.5-0.9.

Also, another question, do you know how to change the permeability with mean pressure?

Thanks again

Hi Hansini

Void Ratio is defined in Abaqus as mentioned in my previous answer (clay, void ratio, height, void ratio, height). Those are found experimentally from isotropic consolidation test (void ratio for the corresponding mean consolidation pressure).

Typically for clayey soil, the void ratio can be greater than one.

Regarding permeability, it has to be found experimentally for the range of consolidation pressure during 1-D test or flexible wall permeameter..

hello my friend

I have some errors

like initial Void Ratio has not been defined

do you know what should I do?

Hi Hansini,

How do you fix it finally? I still encountered similar issures about changing the permeability with other state variables defined in UMATHT. Thanks!

Xi