Rock masses are very complex. Is that a good reason to use something that is so simplistic (GSI) with a numerical range of only 5 to 90? And then combine this with non-empirical equations needing software to use due to extreme algebraic complexity. Applied to tackle the shear strength of rock masses in continuum models, the fact that shear strength is not actually cohesive plus frictional strength (linear or non-linear) but process-dependent (c THEN sigma n tan phi) makes these colourful analyses suspect.
I believe that those colourful analyses are responsive to market requirements within the industry. While technical challenges experienced by engineers are usually beyond the GSI or Mohr-Coulomb representativeness; simplistic solutions are usually the “go-to” recipe (standards?). It seems to me that the will of looking/moving into standardised procedures has become a rule. Simplistic solutions are also sought, because they are seen as time and money “savers”. Also, an approximation might be as suitable as a more precise solution. Despite Geotechnical engineering not being the perfect fit for standardisation practices it offers many benefits. Not a simple problem.
A relevant answer for sure. The problem is the misleading information that may be obtained: exaggerated 'plastic' zones in relation to reality (court case) and in relation to other codes/methods. Rock masses are usually anisotropic. We do rock masses an injustice, rock mechanics practice too,
by assuming 'picture' recognition is enough. We can use a D fudge-factor (any answer for deformation modulus desired) and then rely on software for impossiblly complex algebra, just to complete the illogic nature of this
'time and money saver'.
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