GSI calculator

GSI calculator allows you to calculate the associated parameters for Generalized Hoek-Brown criterion in Define Material Properties. You can define these parameters when Generalized Hoek Brown failure criterion is selected for strength parameters.

Two methods can be used to define the peak strength:

• GSI, mi, d
• mb, s, a

The following parameters as an input when GSI, mi, d, is selected to define the peak strength:

• Intact Compressive Strength
• Geological Strength Index
• Intact Rock constant
• Disturbance factor

are used to calculate:

• mb
• s
• a

you can click on suggestions tab to get a suggestion for each of the parameters.

GSI Picker:

Three options are available for Rock Type: Basic Observational 2000, General Quantitative 2013, and Heterogeneous Rock Mass 2013.

For further information about the Hoek-Brown classification parameters sigci, mi, GSI and D, please consult Hoek, Carranza-Torres, Corkum (2002). To view the paper click here.

Pick Mi value:

Once you have determined a value, select OK in the Pick Mi Value dialog. The value will be automatically loaded into the GSI calculator, and the calculation will automatically be carried out (i.e. output parameters and failure envelopes will be re-calculated using the selected input data). Note that changes in value applies to the selected material.

Distribution Factor (tunnels):

Distribution Factor (slopes):

You can also refer to Rock Mass Modulus for more information on each parameters for rock mass modulus calculation.

If you have selected (mb, s, a) as defined by type, then you will be prompted with inputs as shown below:

where the user defines the known mb, s, and a parameter into the dialog.