Thank you so much for the reply. I re-run the model again and compare the results with and without INISTATE codes. Two models show different results. However, I am not sure if it is the correct result. From my expectation, the stress in the model without pore pressure (total stress) should be equal to the stress with pore pressure (effective stress) minus 22.5 (pore pressure), since the model is in compression and the pore pressure is in an opposite direction. However, the result is not the same as I expected. First figure is the model without pore pressure and the second figure is the model with pore pressure.
Also, after I apply the code, there is always a warning message that says: Solver pivot warnings or errors have been encountered ensuring the solution. This is usually a result of an ill conditioned matrix possibly due to unreasonable material properties, an under constrained model, or contact related issues. Check results carefully.
Any suggestion on these two issues?
Thank you so much in advance for your help.