When having one or more circular tunnel shapes inside a larger circular tunnel with interfaces, PLAXIS 2D AE can have difficulties in finding what the correct side for the interface is.This can happen when e.g.,:
Figure 1. Tunnel geometry with possible incorrect interface
This issue can have the following consequences:
It is not always easy to check if this is happening in the model. If the material assignment in the interface is set to take the material from the adjacent cluster and the materials inside the tunnel and outside the tunnel are different, you can check in your model if this is happening: open the table with interface results, and look at the material dataset reference in the first column. This should refer to the defined material dataset, and not to the material dataset used in e.g. the inside of this arc.
This issue only happens for fully circular tunnels that consist of just one segment.
This issue is now solved since PLAXIS 2D 2015.00: now a circular tunnel will by default consist of two segments in stead of just one. This prevents this issue to occur. Note: for full circular shapes the above mentioned problem may still occur.
For PLAXIS 2D AE, this issue can be solved if instead of one segment the circular tunnel is designed with two segments. For existing models, a simple workaround would be to draw a line over the tunnel such that the entire tunnel will be split into two parts. When designing a new circular tunnel, define two arcs of 180 degrees each:
Now the model will have correct interfaces defined.
Figure 2. Workaround step 1: set the shape to Free
Figure 3. Workaround step 2 and 3: add a segment of 180 degrees and symmetrically close the tunnel
Figure 4. Workaround step 4: Add Properties to the segments