In PLAXIS 2D or 3D, a thick slab can be modelled in two ways:
When using plates to model a thick slab, note that plates are structural elements used to typically model thin structures in the ground with a significant flexural rigidity (bending stiffness).
There are, however, cases when a plate needs to represent a thick concrete slab embedded in the ground. In such cases, the thickness of the plate, which is essentially a surface in PLAXIS 3D and line in PLAXIS 2D, overlaps partially with the soil, depending on the plate’s thickness.
When the plate is representing a slab embedded in the ground, the true volume of the plate is already occupied by soil elements, and the actual weight of the plate, w, is, therefore, the difference between the weight of the plate and the soil occupying its true volume.