Undrained triaxial simulation using FLAC3D

Hi FLAC3D community,

I’m attempting to simulate an actual triaxial test as a boundary value problem. I have created a cylinder respecting the 2V:1H ratio, as in the lab. I’m using the Norsand model. The boundary conditions are as follows: I have applied a normal stress to the zones at the circumference of the specimen. The movement of the top and bottom caps has been fixed perpendicular, allowing them to move freely in the two remaining directions. Although I’m using the fluid module, the fluid activation is turned off. The shearing phase occurs by moving the top and bottom caps with a constant displacement magnitude of 0.75e-6. When I reached 1.6% of axial strain, it became evident that my specimen was not experiencing uniform displacements. Instead, there is a concentration near the top and bottom corners. I’m aware that this is linked to the time I’ve allowed for the pore pressure to adjust to the strain increment. I’m expecting to achieve a uniform displacement contour in the radial direction but have been unsuccessful. Has anyone attempted simulating this or have any advice?

see attached file
Master_txx.dat (5.9 KB)

Grid_building.dat (2.0 KB)

Hello @abarrero,

Have you seen the Undrained Triaxial Test with NorSand Model in our documentation? - Undrained Triaxial Test with NorSand Model — Itasca Software 9.0 documentation
Perhaps this example can help you.

Hey @dblanksma,

Thank you for your prompt reply and yes indeed I have seen this example. The particular example you mentioned it is suitable for one element test, but is not very useful for my problem. Cheers.

Adding more information. I have run the code under drained conditions (without water) and results are a very nice homogenous deformation. I expect the same results for the undrained conditions…Now I’m aware that my results are affected due to the pore pressure presence, however I will investigate an efficient method to achieve a homogenous deformation. I’m also plotting the deviatoric stress evolution until 5% of axial strain at multiple locations: top, middle, bottom.