Problem description

The external waterloads on active model boundaries and/or structures are generated by the Input program prior to the actual (flow) calculation. In general, the calculation kernel copies these external waterloads and transfers them to the Output program after the Finite Element calculation (Note: the calculation kernel only calculates the pore stresses inside the active soil elements). However, due to an issue with the 2D and 3D calculation kernel the external waterloads may be incorrectly overwritten in the case of a flow calculation possibly causing wrong results.

A typical situation where this may occur is indicated below for a 3D situation: a vertical (cantilevered) wall loaded by a water level difference. After the (flow) calculation the external waterloads are incorrect causing wrong results.

Solution

This issue has been fixed in PLAXIS 3D 2013.01.
For PLAXIS 2D, this issue is resolved for PLAXIS 2D AE. Make sure to apply interfaces along the wall to allow the groundwater flow to generate different water pressures on either side of the structure.

Carefully inspect your Output results in case you are running a steady state or transient flow calculation in combination with external waterloads. Possible options are:

• inspect the phreatic level. To switch on the phreatic level, check the item in Geometry > Phreatic level;
• visualize the external water loads in the results plot. External waterloads are shown in blue arrows, see also the images above;
• explicitly check the external waterloads on the different nodes in your model via the menu option Project > Water load information.

If you detect something is wrong in your model you may:

• in some cases use a load to compensate or simulate the wrong or missing external waterloads;
• in other cases a project specific workaround may have to be selected.

If you are unsure if something is wrong in your model and/or what workaround to select please contact our support department.