Use the Constant field stress option to define a constant stress field prior to excavation (i.e. one which does not vary with position or depth). Constant field stress is typically used for excavations which are relatively deep (i.e. not close to the ground surface).
In the Field Stress dialog, the following parameters are used to define a Constant field stress.
Sigma 1
Sigma 1 is the MAJOR IN-PLANE principal field stress.
Sigma 3
Sigma 3 is the MINOR IN-PLANE principal field stress.
Sigma Z
Sigma Z is the OUT-OF-PLANE field stress.
Angle
The Angle is measured between the positive x-axis and the direction of Sigma 1. The Angle is measured in degrees, and the counter-clockwise direction is defined as positive.
Note: remember that the Stress Block indicates the relative magnitude and direction of the In-Plane principal field stresses. If the Stress Block looks wrong then try entering the field stress data again, keeping in mind the definition of Angle. The display of the Stress Block can be toggled on or off in the View menu.
Custom Field Stress
Customized field stress may be defined for individual materials in a model, by selecting the Advanced button, and defining custom field stress as required. See the Custom Field Stress topic for details.
Axisymmetric Constant Field Stress
If you are modeling an Axisymmetric problem (this is set in the Project Settings dialog), then the Field Stress dialog will ask you for:
Horizontal Stress
Vertical Stress
(rather than Sigma 1, Sigma 3, Sigma Z and Angle).
It is important to note that Vertical and Horizontal refer to the setup of your problem in Phase2, and not necessarily the true orientation of your excavation. The Vertical stress is the stress in the axial direction (i.e. the axis of rotational symmetry), and the Horizontal stress is the field stress perpendicular to the axis of symmetry. The terms Vertical and Horizontal are used, because in Phase2, an axisymmetric model must always be defined such that the axial direction is oriented with the y-axis of the coordinate system.
Out-of-plane (or circumferential) field stress exists, but is automatically set equal to the Horizontal (or radial) stress, and cannot be independently varied by the user.
See the Phase2 Tutorials for a tutorial on Axisymmetric modeling.