The Stress Computation Method determines how the 3-dimensional stress distribution due to loading is calculated.
The Stress Computation Method is specified under the General tab in the Project Settings dialog. Two options are available:
Boussinesq
2:1
Boussinesq Method
The Boussinesq method uses the theory of elasticity to calculate the vertical stress under a point load in a homogeneous, semi-infinite half space:
Where 
is the loading stress at any point and the meaning
of the other symbols are as shown in the following figure.
To compute the stresses under a distributed load, the Boussinesq solution is integrated over the area of the footing.
2:1 Method
The 2:1 method assumes that the zone of influence for an applied rectangular load has a slope of 2:1 as shown in the following figure.
The vertical loading stress at some depth is then calculated by:
For a non-rectangular footing, the stress is calculated by computing the area of the load at the surface. With increasing depth, the area over which the load is applied increases at a 2:1 ratio and the magnitude of the loading stress decreases correspondingly.
The 2:1 method is included mainly for purposes of comparison with existing calculations, however, its use is generally not recommended for 3-dimensional analysis, due to the simplistic assumption on which the method is based.
For further information on the stress calculations in Settle3D, see the Settle3D Theory Manual.