PDisp – Does Pdisp always calculate horizontal displacements to be in the direction away from a vertical normal load on a horizontal plane?
Consider the simple example of a rectangular load sitting at 0m elevation on a single layer of soil. (This example assumes that calculation of horizontal displacements has been specified in the Analysis Options input dialog.)
Contours of soil movement in the horizontal Y direction are shown below using a series of displacement grids at increasing depths below the load.
From the plots above it can be seen that, in this example, near the surface the soil displaces towards the centre of the load (the magnitude being greatest under the perimeter of the load) whereas at deeper levels the soil at or close to the perimeter of the load displaces away from the centre of the load (again the magnitude being greatest at the perimeter of the load).
Horizontal displacements are not therefore always away from the load. Pdisp shows that whether they are, and the extent to which they are, is influenced by the horizontal distance from the centre of the load, and the depth of the displacement location beneath the surface. Hence a utility lying both close to the load and close to the soil surface may be drawn horizontally towards the load.