3DEC is commonly used to model rock masses close to the earth’s surface. In these situations, the in-situ vertical stress at each point can be calculated from the weight of overlying material. The horizontal stresses often are assumed to be some proportion of the vertical.
3DEC provides a command, insitu topo, to calculate these initial stresses for each zone. However, this calculation used to be so slow that is was not of practical use. With the latest update of 3DEC (Version 5.00.168 or above), this function has been sped up dramatically to make it useful once again.
The figure below shows vertical stress calculated using the insitu topo command for a model with almost 800,000 zones. The calculation takes a couple of minutes, depending on the speed of your computer. You can see the higher stresses under the mountains and the lower stresses under the valleys. The red circle indicates a geological unit with low density. The zones under this unit therefore have reduced stresses.
The insitu topo command also calculates the stresses on joints as shown in the figure.