How to implement the Mandel's effect with tough-flat coupling

Hello everyone, I'm a student during master's degree and have spent more than a year on tough-flac coupling, but still have some big problems on this field.

I want to achieve direct coupling of Tough2 and Flac3D, using the fixed stress method as Kim mentioned(Kim et al. 2011), not what Jonny did in 2001, which seems like indirect coupling. So I take Mandel's problem as a validation. I have asked some people who have done this, but my advisor did not provide further help, so I only know the key point is to modify the storage term in TOUGH2. As I have no idea about the source code,I just try to modify the porosity in every circle, but the decrease in porosity does not seem to bring about an increase in pore pressure. So the problem is, did porosity have nothing to do with mass conservation? Otherwise according to my understanding, the rapid decrease of volume space should lead to an increase in pore pressure. But I can only get a complete pore pressure dissipation process, which is same to the one-dimensional process, as shown in the attached picture