zone initialize-stresses command


zone initialize-stresses keyword <range>

Primary keywords:

direction-x    overburden    total    ratio

Initialize zone stresses based on the density of the zones above them and gravity.

For all zones in the range, the total column of zone densities above them (opposite the direction of gravity) is accumulated into a stress. The ratio keyword is used to determine both horizontal stresses, and defaults to 1.0. This zone stress state is then initialized to this value.

Note that this works even if gravity is not vertical - in which case the vertical and horizontal stresses are the principal components aligned with gravity and perpendicular to gravity, respectively.

Note that in FLAC3D, compressive stresses are negative.


On rare occasions zone can be distorted enough to cause its centroid to lie outside of the actual zone volume, at least using the assumptions this algorithm makes about non-planar faces. If that zone is also on the model surface, then zone centroid can actually be outside of the model. In this case the initial zone stress will be incorrect.

This command should be used after assigning a constitutive model, setting the gravity and material densities.

The available keywords are:

direction-x v

If two parameters are given for the ratio keyword, then this keyword can be used to specify the local \(x\)-direction the system should use. The \(y\)-direction is determined automatically using the \(x\)-direction and the direction of gravity to create an orthonormal system. The \(x'\)-direction may be adjusted to make it normal to the direction of gravity. By default the \(x\)-direction is (1,0,0).

overburden f

Specifies an overburden stress added to the calculation, assuming the vertical boundary of the model does not represent the surface. This value defaults to 0.0. Remember that compressive stresses are negative, so this value will typically be negative.


By default the vertical to horizontal stress ratio is applied to effective stress. Use this keyword to make it apply to total stress. This has no effect unless a non-zero pore-pressure field has been created.

ratio f <fy >

Determines the horizontal to vertical stress ratio. Both horizontal stresses are set to the vertical stresses times this value. If the optional second parameter fy is given, then a different ratio is used in the local x and y directions. Note that the direction-x keyword is used in this case to distinguish these local directions.