Air duct construction method using existing transverse channel at end of station as side pilot tunnel

The invention belongs to the technical field of tunnel construction, and particularly relates to an air duct construction method using an existing transverse channel at the end of a station as a side pilot tunnel, which comprises the following steps of: respectively constructing side piles in the side pilot tunnel and the transverse channel, constructing middle piles in a middle pilot tunnel, pouring transverse channel and side pilot tunnel pile top beams and primary supports in the pilot tunnels; after construction of side piles in the transverse channel is completed, plain soil and plain concrete are used for backfilling the existing transverse channel from bottom to top in a layered mode and are tamped, an arch waterproof layer is laid in a middle pilot tunnel, and a top longitudinal beam is constructed; the space between the top longitudinal beam and the middle pilot tunnel is backfilled with C20 plain concrete, and interlayer soil between the two pilot tunnels is reinforced through grouting; the existing