Estimation of the geological strength index based on synthetic rock mass model

Reliable assessment of the Geological Strength Index (GSI) is essential for estimating the strength and deformation of rock masses. This study proposes a more objective and data-driven model for GSI estimation. To achieve this, a method that combines the Hoek-Brown (HB) failure criterion and the 3DEC-based synthetic rock mass (SRM), namely the HB-SRM method, is proposed to quantify the effects of rock mass structures and joint surface condition parameters on GSI values. Based on the analysis of the numerical results, a quantitative GSI model in terms of the volumetric joint count ( J v ) and the joint friction angle ( φ ) is proposed and validated. It is found that the values of GSI increase non-linearly with the decrease of J v and increase of φ ; therefore, GSI contours are nonlinear and exhibit variable spacing. In addition, the reliability of the proposed GSI model is further tested through back-analysis of in-situ rock mass deformation tests conducted in exploration tunnels at the dam site. Results show that the proposed model provides a conservative estimate of GSI, which is advantageous for ensuring safe and reliable engineering design. Finally, this study primarily focuses on blocky rock masses; however, the proposed HB-SRM method together with the use of J v and φ can also be used for developing quantitative GSI charts for various rock types.