If you are using the Generalized Hoek-Brown criterion as the strength type for a material, the Parameter Calculator dialog can provide valuable assistance, to help you determine the mb, s, a parameters of the Generalized Hoek-Brown criterion for your material. To use the Parameter Calculator dialog:

In the Define Material Properties dialog, set the Strength Type = Generalized Hoek-Brown.

Set the Define Strength Using option to mb, s, a, and select the GSI calculator button .

This will display the Parameter Calculator dialog, which allows you to calculate the parameters mb, s and a, from values of intact rock constant mi, GSI (Geological Strength Index), and Disturbance Factor, D, according to the equations of the Generalized Hoek-Brown criterion.

Enter values of GSI, mi, and D in the Parameter Calculator dialog, and the corresponding values of mb, s and a will automatically be displayed in the dialog.

NOTE: you can use the Pick buttons to assist you in determining appropriate values of GSI, mi and D, see below for details.

Select OK to return to the Material Properties dialog, and the calculated values of mb, s and a will automatically be loaded as the strength parameters for the material.

This is very useful because the parameters GSI, mi and D are usually the known quantities for a rock mass, whereas mb, s and a are often not directly available.

Pick GSI, mi, D, Intact UCS

Within the Parameter Calculator dialog, you may access interactive tables and charts for:

the estimation of mi based on rock type

the estimation of GSI based on rock structure and surface conditions

the estimation of Disturbance Factor based on excavation type and techniques

the estimation of Intact Uniaxial Compressive Strength (UCS) based on field estimates

Select the Pick button for the parameter that you wish to estimate, and you will see a table or chart which allows you to select an appropriate value for the parameter, for your material.

Direct Entry of GSI, mi and D

As of Slide version 8 the parameters GSI, mi and D can be entered directly in the Define Material Properties dialog by setting the Define Strength Using option to GSI, mi, D. In this case it is not necessary to use the Parameter Calculator dialog.