Soil layers defined by boreholes

When the model width is determined by the soil layers and these soil layers are generated by boreholes, the horizontal model dimensions are defined by the Model Contour in the Project properties (available via the File Menu):

Figure 1. Model contour in PLAXIS 2D AE’s Project Properties

When changing the values for the horizontal dimensions, the soil layer generation will take these horizontal coordinates as limits. For PLAXIS 2D this will be x_min and x_max, and for PLAXIS 3D this will be x_min, x_max, y_min and y_max.

Soil layers in structures mode

If the soil layers in the program are defined by not using the borehole, e.g. Polygons in PLAXIS 2D and Volumes in PLAXIS 3D, this model contour does not define the overall model width. To change the model width, you will need to modify these Polygons (2D) and Volumes (3D).

PLAXIS 2D

To do this in PLAXIS 2D (2D AE.02, and later):

1. double click on a Soil Polygon that needs to be changed
2. The corner points (HelperPoints) are now highlighted by larger black dots
3. These HelperPoints can be moved by dragging them with the mouse
4. Alternatively, in the Selection explorer at the top left, you can now see a list of HelperPoints. These HelperPoints can be modified to change the Polygon’s shape.

Figure 2. Highlighted Helper points of a Polygon (right) and HelperPoints in the Selection explorer (left)

PLAXIS 3D

In PLAXIS 3D, such a volume cannot be modified. A new volume needs to be created in PLAXIS 3D in order to change the model’s width based on volumes.

One approach to extend the width of the 3D model, is by adding the extension as separate volumes:

• Decompose the volume into surfaces (right click the volume and choose Decompose into surfaces)
• Locate the side you want to extend, and click on it
• Now extrude it in the direction you want the model to expand
• The surfaces created in the first step can be removed again. Note that the last created group will contain these surfaces.

This needs to be repeated for each volume that form the boundary.

For reducing the size of the model, .i.e. removing part of the volumes:

1. Draw a surface on the location of the newly intended vertical model boundary
2. Select the volume and the just created surface, press right mouse button and select intersect and recluster.
3. The original volume is now split: delete the surface created in step one as well as the unwanted volume that is now outside the desired model.

Repeat the steps above for each model boundary.