Hyperelastic UMAT using *Soils - non-convergence

Hi everyone,

I am trying to model fluid flow through a porous material. I have modeled the solid matrix in UMAT as a type of hyperelastic material, and I would like to use the SOILS consolidation to do the analysis, however, even though according to the following thread it seems doable, it seems like it's not working when I use *Soils.

It's an unconconfined compression simulation. The problem is defined as a displacement control problem and I want to model a Stress-Relaxation process. I'm applying 10% strain using a tabular amplitude:

• 0s, 0  
• 1s, 1
• 5s, 1

I have examined a couple of test cases:

• I tested the input file using Abaqus built-in elastic material for the solid matrix, solving with *Soils, and it works fine and I get what I expected.
• I tested the input file using Abaqus UMAT elastic material for the solid matrix, solving with *Soils, and it works fine and I get what I expected.
• I have checked the UMAT using the same input file only with a simple static step, and replacing the elastic solid matrix with the UMAT. That works fine too.

The pore pressure showed a discontinuous profile like this: 

Please let me know if you have any experience with this.

Thanks ?

Victor