Improving the Hoek-Brown criterion based on the disturbance factor and geological strength index quantification

A supplementary quantified approach for the GSI system is proposed by focusing on improving the GSI and the rock mass disturbance factor (D). The surface condition rating (SCR), the structure plane condition factor (Jc), the rock mass basic quality index (BQ), and the rock mass structure rating (SR) are used in the proposed method. An improved formula for the disturbance factor (D) using the BQ is established. With this method, the GSI value is a set of possible numbers within given intervals rather than a constant value. The relationship between the GSI and rock mass D reflects not only the disturbance degree of the rock mass from the wave velocity but also the difference in the disturbance degree from the strength, which increases the accuracy of the D value. In addition, because of the value of the standard differences among the SCR, Jc, BQ and SR, the GSI region may be considerably wider due to quantification factors with larger differences. Thus, the method of measuring the interval value can maximize error reductions, and intermediate interval values are recommended for use.