There are two options to model a massive tapered pile easily:

1. Using the cone

This shape of a tapered pile can be achieved by making use of the "cone" command.

1.1 Cone command

cone <base radius r_b> <height h> [<top radius r_t>] <point> <directionvector>

with

• radius r_b = Dtop /2 (Dtop is diameter at the top of the pile)
• coneheight h is height of the total cone structure
• optional radius r_t at the (truncated) top
• point is the center point for the cone’s base
• direction vector tells in which direction the cone should be pointing. For a vertical tapered pile this should be (0 0 -1)
• Note: the cone command only creates the volume.

1.2 Soil structure interaction

When one wants to model soil-structure interaction, interfaces should be added:

• Select the cone's volume;
• Use the right mouse button (RMB), and select Decompose into surfaces to make surfaces on the outside of the cone;
• And now apply outside (positive) interfaces to the three surfaces.

1.3 Pile activation

This concludes the geometry creation. To activate the pile for the calculation, make sure to change the soil material inside the pile volume into the pile’s material in the appropriate phase including activation of the interfaces.

2. Import from CAD

Of course it is always possible to model the geometry in a third party CAD program and then import this geometry in PLAXIS 3D. See How do I import a geometry in PLAXIS 3D? for more tips on importing

After importing, make sure to add interfaces to properly model soil-structure interaction.