Hoek-Brown - pore pressure and Safety Factor

Hello everyone,

My first question here in the forum!

I'm modeling a set of foundations on weathered granite and I'm using the Hoek-Brown (HB) model. Everything in the material model works perfectly fine, however, three questions regarding the material model behavior surge:

1 - Does water/pore pressure have a relevant effect in the HB behavior?

2 - Aiming to understand the influence of pore pressure in a footing over a rock mass using HB, I did some simple models with a rectangular surface load with a pressure of 500 kPa. Without pore pressure the SF analysis runs without any problems, however, When there is pore pressure, the Safety Factor analysis has a very bizarre behavior. What should I conclude about this, that one can not rely on this analysis when there is pore pressure, or more generally that one should use this analysis with Hoek-Brown carefully? 

     2.1 - If instead of modeling the footing as a surface, I model it as a rigid body loaded with a point load on the top surface with a load that would develop a pressure of 500 kPa in the rock,  there isn't such behavior with the pore pressure. How does the way I model the footing influence the final results? 

Below I show two pictures of the safety analysis when the groundwater head is set equal to the top surface of the rock and when there is no groundwater at all. The atypical behavior of the SF analysis when there is groundwater, on the left, is quite obvious if compared when there is no groundwater head (on the right)

Fig. 1 : LEFT: SF analysis for HB model with  z_groundwater = 0. RIGHT : SF analysis for HB model with NO water.

If modeling the footing as a rigid body the results are also quite different:

Fig. 2 : LEFT: SF analysis for HB model with  z_groundwater = 0. RIGHT : SF analysis for HB model with NO water

Should I expect changes in the safety factor due to the water pore pressures? Does the way I model the footing really influence the final results?

Thanks in advance,

My kindest regards,
Afonso