Problem description

Interfaces in PLAXIS have an active setting for the deformation calculation (soil structure interaction) and an independent active setting for flow calculations (as an impermeable screen).

Figure 1. Interface setting in Selection Explorer

The default behaviour is that the interface will be deactivated for the deformation analysis, while the permeable state is activated.

The two settings are totally independent for the calculation, and so these two options can also be set indepently.
However, in the user interface, when activating the interface for the deformation part, in 99% of the cases this interface will probable need to be set to impermeable as well (for example when activating an excavation wall with interfaces, activating a tunnel lining with interfaces). For the user’s convenience, when activating the interface, it will also be set to impermeable (by deactivating the permeable checkbox).

Figure 2: Interface activation behaviour for soil-structure interaction setting

Note that when deactivating the interface, it will not be automatically set to permeable.

In PLAXIS 2D AE.00 and PLAXIS 2D AE.01 this actual interface setting for the permeability is however not easy to check in the graphical model: in the Water conditions mode the visualization of the interfaces is not reflecting the correct permeability state, but is showing a mixed state of the two settings (deformation and flow). This interface permeability state is also not shown in the Output program: only the deformation setting is visualized in Output.

Figure 3. Example of interfaces in water conditions mode for 2DAE.01:
both appear to have the same settings, but on the left the interfaces are
set to permeable and on the right to impermeable

Solution

This issue is now solved in PLAXIS 2D AE.02: when an interface is set to impermeable, this impermeable interface will be shown with an orange colour indication, see Figure 4.

Figure 4. Example of interfaces in water conditions mode in PLAXIS 2DAE.02:
impermeable interfaces are drawn in orange (left),
permeable interfaces are grey (right)