During an undrained excavation/unloading (positive) tensile excess pore pressures (pexcess) may develop. Depending on the steady state pore pressures (psteady) the resulting total pore pressures pactive (which is the summation of the psteady and the pexcess) may also become positive in a certain area. However due to an issue in PLAXIS Output all tensile total pore pressures (total suctions) are always cut off at zero in the pactive plot and table. This is not correct!
Since the total (Cartesian/Principal) stresses plot is a summation of the effective stresses and total pore pressures, the total stresses plot is also not correct in this situation.
Note that this issue is purely an Output issue in PLAXIS 2D 2012.00: the calculation kernel still uses and saves the correct values. The values shown in these Output plots and tables are correct:
There is no direct work around available to show the correct pactive and/or total stresses plot. However when in doubt on the results of the pactive plot the correct total pore pressures can be checked by (manually) adding the pexcess and psteady for some nodes/stress points (by using the Hint window for example). The correct total stresses can now be checked by (manually) adding the pactive and the effective stresses.
This issue is solved since PLAXIS 2D2012.01