Problem description

During an undrained excavation/unloading (positive) tensile excess pore pressures (p_excess) may develop. Depending on the steady state pore pressures (psteady) the resulting total pore pressures p_active (which is the summation of the p_steady and the p_excess) 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 p_active 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:

• effective stresses
• steady state pore pressures: p_steady
• excess pore pressures: p_excess

Solution

There is no direct work around available to show the correct p_active and/or total stresses plot. However when in doubt on the results of the p_active plot the correct total pore pressures can be checked by (manually) adding the p_excess and p_steady for some nodes/stress points (by using the Hint window for example). The correct total stresses can now be checked by (manually) adding the p_active and the effective stresses.

This issue is solved since PLAXIS 2D2012.01