Quantification of the GSI and D values in the Hoek-Brown criterion using the rock quality designation (RQD) and discontinuity surface condition rating (SCR)

Quantitative determination of the important parameters in the Hoek-Brown (H-B) failure criterion, i.e., geological strength index (GSI) and disturbance factor (D), is essential for increasing the design reliability of rock engineering projects. Thus, the problems that this research addresses are (1) the need for a new quantification of GSI which can adhere to its original definition and (2) the need to quantify D. Specifically, a quantitative expression is established to allow GSI values to be estimated based on the rock quality designation (RQD) and surface condition rating (SCR) of the discontinuities in rock masses (SCR depends on the infilling, weathering, and roughness ratings of the discontinuities in the rock mass). A quantitative method for determining the value of D was subsequently developed based on the improved GSI estimates. A new improved H-B failure criterion for determining the mechanical parameters of the rock mass was thus generated based on the original H-B failure criterion and new improved GSI and D values. The improved H-B failure criterion was tested by applying it to the Chengchao Iron Mine in China. The mechanical parameters of the rock masses in the mine area were estimated using the improved H-B failure criterion (considering the results of rock mechanical laboratory tests and RQD and SCR values derived from a statistical analysis of drill cores and field investigations). The results of long-term in situ monitoring tests further verify the rationality of the deformation and strength parameters estimated using the improved H-B failure criterion. The improved method provides a new way of quickly estimating the mechanical parameters of rock masses when there are insufficient available test data.