Abstract: The traditional construction method for a super large crosssection highway tunnel is characterized by a complex process and low efficiency. Accordingly, the active steel framerock wall combined support method is proposed for the largespan section of the bifurcated tunnel #2 of the Haicang Shugang channel on the Xiamen Lu′ao Road (the largest crosssection highway tunnel under construction in China) based on the idea of "replacing support by cable" and the characteristics of high strength of surrounding rocks. Next, the mechanical parameters of surrounding rocks are obtained by the rock triaxial compression test and the HoekBrown estimation method, and the rationality of the method is verified by numerical simulation. Meanwhile, the length of the prestressed anchor cable is determined to be 10 m and the prestress value is 1 000 kN. Finally, the construction mechanical characteristics are analyzed. The results show the flowing. (1) Deformation of the surrounding rocks mainly occurs before the rock wall excavation (#5); the main deformation is the vertical deformation, and the top heading excavation is the main cause for tunnel arch settlement and invert uplift. (2) Under the action of the prestressed anchor cable, the excavation of tunnel rock wall (#5) and removal of the middle partition wall has little impact on the surrounding rock deformation and primary support internal force. (3) The compressive stress at the primary supporting arch foot is concentrated, and the crown and invert are subjected to greater tensile stress. (4) Deformation of the rocks surrounding the tunnel and the primary support bearing capacity meet the safety requirements of highway tunnel construction, indicating that the construction method has certain reliability and safety.

Key words: highway tunnel, singlespan fivelane, large crosssection, construction method optimization, numerical calculation, rock triaxial compression test, construction mechanical characteristics, steel framerock wall combined support