Abstract: To further explore the structural force characteristics of support structures during excavation of Yangcheng tunnel of HaolebaojiJi′an railway in weathered red sandstone stratum, the safety of support structure is analyzed based on insitu monitoring results The results show the following. (1) The surrounding rock is seriously unsymmetrialloaded, which would lead to squeeze in tunnel. Therebench method and composite lining can guarantee the stability of tunnel structure. (2) The maximum compressive pressure between the primary support and the secondary lining is only 22.4% of that between the surrounding rock and the primary support. The load bore by primary support is larger than that bore by secondary lining, and the secondary lining is mainly used as a safety stock. (3) The maximum compressive stress of shotcrete is 41.3% of the ultimate strength, the maximum tensile stress is 88.0% of the ultimate tensile strength, and the maximum compressive stress of grid steel frame is 53.8% of the ultimate strength. The safety factor of the most unfavorable position of the secondary lining is 28.55, indicating that the properties of the primary support are not fully utilized. (4) The shotcrete and steel frame coordinate well, and the primary support should be well utilized to control the deformation of surrounding rock in practical engineering.

Key words: railway tunnel, fullyweathered red sandstone, primary support, secondary lining, structural safety, insite monitoring