Abstract:In response to the common problem of secondary lining cracking in double-arch tunnel without middle drift, how to improve its mechanical characteristics to ensure the safety of tunnel construction and operation is the focus of this study. Based on the arch section of a highway tunnel in the southwest mountainous area, numerical simulation method was adopted, the influence of support parameters such as the thickness of the initial support, the spacing of the steel frame, and the thickness of the secondary lining of the advanced tunnel on the displacement of surrounding rock, the mechanics characteristics of the initial support and the secondary lining of the advanced tunnel were deeply studied, and reasonable and optimized support parameters were proposed. The results show that as the thickness of the initial support increases or the spacing of the steel frame decreases, the displacement of the surrounding rock of the advanced tunnel and the principal stress of the secondary lining continue to decrease, and the principal stress of the initial support continues to increase. Among them, the maximum tensile stress of the secondary lining decreases significantly. When the thickness of the initial support is 0.28m or the spacing of the steel frame is 0.5m, the maximum tensile stress decreases by about 15% compared with the most unfavorable condition. As the thickness of the secondary lining increases, the displacement of surrounding rock, the principal stress of the initial support and the secondary lining of the advanced tunnel decrease significantly. Compared with the thickness of the secondary lining of 0.7 m and the thickness of the secondary lining of 0.5 m, the maximum tensile stress of the secondary lining is reduced by 23.8 %. Therefore, moderately increasing the thickness of the initial support or decreasing the spacing of the steel frame or increasing the thickness of the secondary lining can effectively improve the stress of the secondary lining. It is suggested that the thickness of the initial support of the advanced tunnel should be 0.28m, the spacing of the steel frame should be 0.5m, the corresponding steel frame type is I22b, and the thickness of the secondary lining should be 0.7m under the shallow buried state of V-class surrounding rock.