Problem description

In some cases when using a PLAXIS 3D AE model with tunnels, it can happen that the external water pressures (water loads from a water body acting on a free surface) are not applied correctly on the tunnel circumference. This is important for when for instance modelling a grout pressure by using a user defined pore pressure.
This, of course, will not give the expected results of an analysis.

You can see this happening when inspecting a phase’s preview or its result, for which part of the geometry does not have external water loads applied at all.

 

Figure 1. Example of missing external water loads

Solution

This issues is resolved since PLAXIS 3D 2016.01

When the above happens in your model, it can be solved by splitting the existing polycurve of the tunnel into two parts. The following can be done, for example:

1. go to Structures mode and select to edit the specific tunnel
2. add a horizontal subsection line
3. intersect the horizontal line with the existing tunnel
4. delete the just created horizontal line (not needed in the geometry, we only need to create two sections here)
5. do not forget to Regenerate the tunnel!

Figure 2. Horizontal subsection line to intersect the existing tunnel