Abstract: During the excavation of extremely soft coal roadways, advanced support techniques are commonly employed to ensure construction safety. To investigate the stability of the excavation face under such advanced support conditions, this study develops a combined failure model comprising an inclined prismatic body and a logarithmic spiral surface. This model is developed based on the Hoek-Brown failure criterion and accounts for the effects of advanced support mechanisms. By integrating the upper-bound limit analysis method, strength reduction approach, and geometric equivalence techniques, an objective function for stability safety factor applicable to non-circular roadway faces is derived. A computational program is then implemented to evaluate the stability safety factor, and the results are compared with those from existing studies to validate the rationality and applicability of the proposed method. Furthermore, the influence of various factors on excavation face stability is systematically analyzed. The findings reveal that the proposed method provides a more accurate representation of the nonlinear failure behavior of surrounding rock across different stress zones. Among the influencing parameters, the internal friction angle of the surrounding rock exerts the most significant effect on enhancing excavation face stability. Additionally, increasing the cross-sectional area of advanced pipes and reducing their ring spacing both contribute to improved face stability. The installation of face bolts proves to be a critical support measure for maintaining excavation face stability. Notably, different geometric equivalence methods yield substantially varied results in computing the stability safety factor for non-circular roadway faces.

Key words: Hoek-Brown criterion, upper-bound limit analysis method, stability safety factor, excavation face stability