GiD forum

Dear CB community,

does anyone know how to set up a simulation of an undrained TX test in CB?
My steps are:
1. Define geometry 1x1m
2. Create material with BBM constitutive model and assign to surface
3. Fix bottom of model in y direction
4. Assign initial porosity and initial suction (0 for full saturation)
5. Set up 2 intervals: 1st for consolidation and 2nd for shearing
6. During interval 1, assign to bottom boundary a Seepage Line Flux condition with Gamma liquid = -1e6 (to simulate drainage during the consolidation)
7. During interval 1, assign isotropic stress of 0.5 MPa on 2 side boundaries and the top boundary
8. During Interval 2, I apply a vertical line displacement rate to the top boundary (strain control test) and I make the bottom boundary impermeable
9. Mesh using 1 quadrilateral element with 4 nodes.

For some reason, this strategy has failed me and I am very stuck. I would appreciate it very much if anyone can help me fix this problem. without this, my masters research cannot continue.

Best regards,
Boris

I have attached my CIU test with the described steps above.
Please help.

Dear Boris,

There might be more problems, but the main problem of your simulation is that the whole model is free to move in the x direction, so even if there is a slight difference in the stresses applied to the right or left, the model will move to the infinite (or -infinite). One possible solution for that is to fix the bottom line of the model both in x and y directions.

Regards,

Alfonso

Dear Alfonso,

thank you for the input. Yes you are right, if only y is fixed the whole model starts moving. I fixed both x and y and the problem still persists.

Best regards,
Boris

That's probably because you are using a single element, and you cannot simulate a single element in Code_Bright; you need al least more than one due to the algorithm used by Code_Bright to reduce the matrix bandwidth.