Geological strength index-slope: an adaptation of the geological strength index system for use in the rock slope stability assessment

T he Geological Strength Index (GSI) system is the basis of parameters used in the Hoek-Brown failure criterion for rock mass strength esti-mation. T he author tested this system and here suggests a modified GSI called Geological Strength Index-slope (GSIslope). T he modified system combines two different existing approaches: the GSI system and Slope Mass Rating (SMR). T he purpose of GSIslope is to allow engineering geologists to quickly evaluate the stability of natural and excavated slopes or open-pit mining in the field. GSIslope is computed by subtracting a constant value of 10 and the multiplication of adjustment factors for discontinuity orientation and slope (F1, F2, and F3, based on the parallelism of discontinuity and slope, discontinuity dip angle, and the difference between the inclination angle of discontinuity and slope) from GSI, and adding field groundwater rating to it. Modified curves are also proposed in this work to determine the accurate ratings of the adjustment factors. T he results of this work are compared to the values obtained from equations of continuous-SMR and SMR-value itself for both the adjustment factors and GSIslope values. T he comparison showed that the proposed curves and GSIslope equation are valid and easy to use for estimating the adjustment factors' ratings and GSIslope value.