Study on Applicability of Double Layer Superimposed Primary Support Arch Cover Method for Large-Span Station in Upper Soft and Lower Hard Stratum

The Qingniwaqiao Station from Dalian’s 5th Metro Line in China has exhibited extremely complicated stratum structure, named as the upper soft lower hard (US-LH) stratum. In accordance with the characteristics of the stratum in which the station is located, the special structure form of double layer superimposed primary support arch cover method is presented. Numerical simulations and field monitoring are carried out to study the construction process. Subsequently, the double-layer primary lining, anchor and steel pipe pile are compared and analyzed respectively. The results show that the double-layer primary lining increases the safety reserve when the initial support is removed, and it can beneficially inhibit the deformation of the arch structure resulting in smaller ground surface subsidence. Anchor and steel pipe pile enhance the bearing capacity of rock mass on both sides of the station. The method has advantages in ground surface subsidence control and supporting structure safety. It is safe and feasible to create a large-span subway station using double layer superimposed primary support arch cover method in US-LH relative stratum.