Abstract: Based on the advantages and disadvantages of the cover excavation method, secondary lining arch cover method and double side-drift method, the double-layer initial support arch cover method is a fast construction technology for mined large-span tunnels, which is suitable for the upper-soft and lower-hard composite strata and integrates the design concept of "bridge arch" structure. Taking the typical upper-soft and lower-hard composite strata in Qingdao area as the engineering geological background, and based on the comprehensive investigation, statistics and summary of the distribution patterns and characteristics of the geotechnical parameters of the deep rock and soil masses, it establishes a structural stability analysis model for arch-covered tunnels with arch section constructed by the CD method, using the "rock thickness-span ratio" at the arch foot as the control variable. The structural deformation patterns and the plastic zone distribution characteristics of the rock mass at the arch foot are analyzed, summarized under different combinations of arch foot bedrock lithology + overburden rock thickness, and the corresponding engineering support plans and control measures are put forward. It is recommended that priority should be given to placing the arch foot on the slightly weathered bedrock, while the depth of the arch foot embedded in the rock being no less than 4 m, which could not only reduce the burial depth of the arch top, control structural deformation and reduce construction risks but also save the cost of sidewall support and realize fast construction without bracing, achieving significant engineering and economic benefits.