Abstract: To explore the suitable construction methods for tunnels subjected to unsymmetrical loads and asymmetrically optimize supporting structures, a case study is conducted on Fulong tunnel on Jiumian expressway. According to the field monitoring results of asymmetric surrounding convergence and surface settlement, a threedimensional mountainous model is established to perform comparative analysis on different construction methods and deformation of support structure and asymmetric design optimization for primary support thickness, anchor rod length, and inclination. The results show the following. (1) The onsite monitoring shows that both the surface settlement and the surrounding convergence are significantly asymmetric. As the distance from the tunnel center increases, the surface settlement reduction on the deepburied side is slower than that on the shallowburied side. The upper arch waist of the deepburied side has the largest convergence value and large fluctuations, while the lower arch waist of the shallowburied side has a slower convergence rate. (2) The center diaphragm method is more suitable for unsymmetricallyloaded tunnel, which can effectively control the displacement of the soil and supporting structure, the anchor rod stress, the primary support compressive stress, and the distribution of the plastic zone. (3) The thickness of the primary support on the shallowburied side is reduced by 2 cm, and that on the deepburied side is increased by 2 cm in asymmetric design optimization of primary support, which can control the tensile stress of the secondary lining within a small value. (4) The length of the anchor rod on the shallowburied side is reduced by 0.5 m, and that on the deepburied side is increased by 0.5 m in asymmetric design optimization of anchor rod, which can uniform the anchor rod stress and reduce the plastic zone on right upper arch shoulder and the left lower arch foot. The primary support stress on the right upper arch shoulder and left lower arch foot unsymmetrically distributes, the situation can be improved by tilting the anchor rod at the right upper arch shoulder towards the deepburied side.

Key words: unsymmetrical loading tunnel, construction method; asymmetric design optimization, numerical analysis, field monitoring