When running an Undrained C (or total stress) analysis no longer a separation is made between effective stresses and pore water stresses in the calculation kernel; the calculation only “knows” one (total) stress. As a result the pore water stresses do not exist in the definition of this material type and Output should not show these pore water stresses. However due to an Output issue non-zero active pore water stresses are shown when selecting an interface. As a result also the total stresses in the interface are shown incorrectly.
Note that this is only a bug in the display of the interface results. The calculation results itself are correct.
This issue is now resolved in PLAXIS 2DAE.00.
For older versions, the pore water stresses and the total stresses plot for interfaces when using an Undrained C material should be ignored by the user.