The Galongla tunnel of Zhamo Highway in Tibet was constructed under complex geological conditions and influenced by geological structure. Joint and cracks of stratum in the tunnel portal are developed extremely. The main characteristics of surrounding rock are low strength and bad self-stability which have great influence on the safety of tunnel construction. Through numerical simulation

the stability of surrounding rock and supporting structure is studied by using whole section method

bench method and CD method to excavate in broken stratum. The three-bench method appropriating for broken rock mass characteristic of Galongla tunnel is proposed. On this basis

the stability of surrounding rock during excavation process using three-bench method is studied by 3D numerical simulation; and the stress and deformation condition of surrounding rock and lining during excavation process are also researched. The results provide a theoretical basis and practical experience for this tunnel and similar engineering construction