Method for large-section underground excavation underpass of existing subway station

The invention discloses a method for large-section underground excavation and underneath pass of an existing subway station, and relates to the technical field of subway design, and the method comprises the following steps: S1, unloading the soil covering load of a top plate of the existing station; s2, excavating and supporting small pilot tunnels below the middle columns of the existing station in the spaced blocks; s3, after supporting is completed, a temporary supporting system is constructed at the position of a base in the excavated small pilot tunnel, and the temporary supporting system is supported between the base of the small pilot tunnel and the top of the existing station; s4, excavating and supporting the remaining pilot tunnels in the spaced blocks; s5, constructing a secondary lining structure of spaced blocks; s6, the steps S2-S5 are repeated, the remaining blocks are excavated and supported, and lining structures of the remaining blocks are constructed; and S7, after the lining structure is c