Plot > Stress > τoct   Octahedral Shear Stress

  Plot > Stress > σmean   Mean Stress

Contours the octahedral shear stress

τoct = ¹/3 [ (σ1 - σ2)² + (σ2 - σ3)² +(σ3 - σ1)² ]½

and mean stress

σmean = ¹/3 (σ1 + σ2 + σ3)

These components can be accessed via the Stress Components toolbar as follows:

This toolbar can be changed to a vertical orientation by dragging is against either the right or left hand edge of the main window.

It can be changed back to a horizontal orientation by dragging is against either the top or bottom edge of the main window.

Selecting the button on the Contours toolbar activates the Stress Components toolbar.

In elastic analysis the octahedral shear stress is normally used with the mean stress and the Drucker-Prager strength criterion

Plot > Strength Factors > Strength Parameters

to estimate the amount of damage due to over-stressing. Since none of the parameters have any orientation sensitivity, this criterion is representative for homogeneous rock mass stability.

By contrast, in non-linear analysis the stresses can never exceed the strength unless some creep is used. In this latter case, viscous creep can allow stress states above the failure criterion, thus indicating a lack of static equilibrium. Hence for non-linear analysis one normally directly considers the amount of non-linear strain or the strain rate predicted by the model

Mohr-Coulomb in 3D FF blocks.

Over-stressing can be presented in several forms including:

Plot > Strength Factors > SF-C   Strength/Stress

Plot > Strength Factors > dToct   Excess Stress

Plot > Strength Factors > dS1   Excess Stress

Plot > Strength Factors > dTmax   Excess Stress

The contour range is set using

Plot > Range

Any of these components can be added to the contouring toolbar if desired

Tools > Configure Contouring Toolbar > Stress

The user may find it handy to add the

More Stress Components

button to the contouring toolbar for quick access to all stress components.