Tunnel formwork is a kind of combined type formwork, which combines the formwork of cast-in-place wall and the formwork of cast-in-place floor on the basis of the construction of large formwork, so as to support the formwork once, tie the steel bar once, and pour the wall and formwork into shape once at the same time. Because of the extra shape of this formwork is like a rectangular tunnel, it is called tunnel formwork.