Correlation Coefficient

If you are performing a Probabilistic Analysis with RocSlope2, and you are using the Mohr-Coulomb strength criterion, you may define a correlation coefficient between Cohesion and Phi (friction angle), for each Joint Property, as described below.

It is known that Cohesion and Phi are related in a general way, such that materials with low friction angles tend to have high cohesion, and materials with low cohesion tend to have high friction angles. The Correlation Coefficient option allows you to define the correlation between these two variables.

By default, when the check box is not selected, Cohesion and Phi are treated as completely independent random variables.

The Correlation Coefficient option is only applicable under the following circumstances:

1. The Strength Model = Mohr-Coulomb.
2. The Random Variables = Parameters.
3. Both Cohesion and Phi are defined as Random Variables (i.e. assigned a statistical distribution).
   
4. The Correlate Cohesion and Phi checkbox is selected.

If all of these criteria are met, then you can enter a value of the correlation coefficient and have it be incorporated into the analysis.

A negative correlation coefficient is usually used to correlate cohesion and friction angle because the variables are inversely correlated (i.e. high friction angle usually implies low cohesion and vice versa).