Abstract: To study the stability of surrounding rock and support parameter optimization under fullface mechanization of highspeed railway tunnels, accurate and credible numerical calculation parameters are obtained through routine rock triaxial tests based on the Liuyuan tunnel of the HuanggangHuangmei highspeed railway. Under engineering conditions, the strength reduction method is used to numerically calculate the safety factor, which is used as an evaluation index for the stability of surrounding rock. Additionally, the crown settlement and sidewall convergence displacements are taken as quantitative indicators to evaluate the stability of the surrounding rock. Further, the optimization of the supporting parameters of the supporting project is performed, and the reasonable primary supporting parameters suitable for the supporting project are obtained. Finally, the stability of the surrounding rock with the optimized support parameters is verified using onsite monitoring data. The following results are obtained. (1) The fullface mechanized excavation of the doubletrack highspeed railway tunnel has a good selfstabilizing ability, and the crown settlement and sidewall convergence are sensitive to the change in reduction coefficient. (2) The crown settlement and sidewall convergence can be used as evaluation indicators to obtain the optimal support parameters suitable for supporting projects. (3) The onsite monitoring data verify the rationality of the optimized support parameters.

Key words: railway tunnel, strength reduction method, surrounding rock stability, support optimization, onsite monitoring, fullface mechanical excavation