Strength Factor

The Strength Factor option will plot contours of strength factor around the excavation(s).

The strength factor is calculated by dividing the rock strength (based on your failure criteria) by the induced stress at every point in the mesh. All three principal stresses have an influence on the strength factor (Sigma 1, Sigma 3 and Sigma Z), so the strength factor in RS2 can be considered 3-dimensional.

In the case of Elastic materials, the strength factor can be less than unity, since overstressing is allowed. In the case of Plastic materials, the strength factor is always greater than or equal to unity. The strength factor is not recommended to be used for plastic materials especially with residual strength as highly plastic regions can generate cases that Strength Factor is less than unity. It is a tool meant to estimate possible areas of high yielding when first conducting the analysis with elastic materials or to reinforce observations when using plastic materials. It is more reliable to look at where elements are yielding and how this affects deformation.

The following document gives the equations used to calculate Strength Factor in RS2, and also the calculation of the Number of Load Steps on strength factor: Strength Factor Equations.

In RS2 2019, only materials with:

• Mohr-Coulomb
• Generalized Hoek-Brown
• Hoek-Brown
• Drucker-Prager
• Cam-Clay
• Modified Cam-Clay
• Discrete Function

As the strength type are supported. Anisotropic and Slide material models are not supported.

Tension

When Tension is indicated in the strength factor contours, this means that Sigma 3 is less than the calculated negative stress (Tension) cutoff for the failure criterion in use.