Determination of the attitude correction coefficient for dominant structural planes in surrounding rock classification and dynamic anchoring

Discontinuities directly affect the global and local stability of rock tunnels, and the spatial relationship between the orientation of dominant discontinuities and the tunnel axis is also adopted as one of the three major correction factors in the Standard for Engineering Classification of Rock Masses. However, because rock mass structures exhibit diverse spatial distribution characteristics and combination patterns, current Chinese industry specifications and standards provide relatively broad reference ranges for this factor, which leads to considerable subjectivity in classification results.To address this issue, this study developed a jointed rock mass model that retained only the controlling discontinuities based on multiscale DFN-DEM equivalent modeling. The model was used to systematically analyze the stability states of tunnels under different combination patterns of dominant discontinuities. The results revealed how the combined effects of the angle between discontinuity strike and tunnel axis, together with discontinuity dip angle, influence the global deformation and stress response of surrounding rock as well as the collapse of local block groups. On this basis, this study refined the value assignment criteria for the discontinuity orientation correction factor K₂ in the BQ method. Accordingly, this study proposes a targeted rock bolt support design method that considers different spatial distribution characteristics of discontinuities. By dynamically adjusting rock bolt parameters in key zones of the surrounding rock, the proposed method effectively anchors locally unstable block groups. The results provide theoretical guidance and engineering value for the refined classification of surrounding rock grades in jointed rock mass tunnels and for the optimization of targeted anchoring design for locally unstable blocks.