Underground excavation station large-span air duct half-range cantilever jacking main body device and construction method thereof

The invention discloses an underground excavation station large-span air duct half-range cantilever jacking main body device and a construction method thereof. The device comprises a first connector section arch cover secondary lining, the outer surface of the first connector section arch cover secondary lining is sequentially covered with a steel frame and an outer-layer tunnel portal frame from inside to outside, the steel frame comprises a first inner-layer grating steel frame and a second inner-layer grating steel frame which are arranged side by side and are the same in structure, the outer-layer tunnel portal frame is located above the first inner-layer grating steel frame, and the width of the outer-layer tunnel portal frame is the same as that of the first inner-layer grating steel frame; a second connector section arch cover secondary lining is connected to an inlet of the first connector section arch cover secondary lining, the second connector section arch cover secondary lining is symmetrically co