How does the Geological Strength Index (GSI) relate to the expected advance rate of a TBM?

The Geological Strength Index (GSI) is a numerical index that estimates the reduction in rock mass strength for various geological conditions. It is directly related to the expected advance rate of a TBM: a higher GSI generally corresponds to a higher expected advance rate, while a lower GSI indicates a lower expected advance rate. The GSI considers factors like the intact rock strength and the characteristics of discontinuities (joints, fractures) within the rock mass, such as their spacing, condition, and pers....