Determination of Rock Mass Parameters for the RHT Model Based on the Hoek–Brown Criterion

When tunnels are excavated in rock masses using the drill-and-blast method, determining the extent of blast-induced damage is a significant concern for engineers in terms of safety and cost. This study establishes a quantitative method to calculate the geological strength index and disturbance factor of a rock mass based on P-wave velocity. A case study was conducted to estimate the strength and deformation modulus of a rock mass in an excavation-damaged zone (EDZ) using the modified Hoek–Brown criterion. The results showed that blasting has a considerable weakening effect on the surrounding rock mass, resulting in reductions in compressive and tensile strengths of > 70% and > 90%, respectively. The Riedel–Hiermaier–Thoma (RHT) model in LS-DYNA software was then used to assess the rock mass damage induced by millisecond delay blasting. In this simulation, rock mass parameters estimated by the modified Hoek–Brown criterion were selected to calibrate the RHT model parameters. In addition, an in situ tunnel blasting experiment was used to verify the calibrated parameters of the RHT model. The modeled extent of the EDZ was 1.6 m, and this showed good agreement with field test results. Therefore, this study provides an effective approach to evaluate blast-induced damage during rock mass excavation.