Multi-layer viaduct erecting construction method

The invention discloses a construction method for erecting a multi-layer viaduct. Used equipment comprises a beam lifter, a bridge erecting machine, an upper-layer beam transporting vehicle, a lower-layer beam transporting vehicle and a lower guide beam. The portal girder lifter lifts a bridge to the girder transporting vehicle, the girder transporting vehicle transports the bridge to the vicinity of the bridge girder erection machine, the girder transporting vehicle is matched with the guide girder to transport the bridge to a specified girder lifting position, and then the bridge girder erection machine lifts the bridge and places the bridge to a specified position. The bottom-layer bridges are firstly mounted, and then the upper-layer bridges are mounted one by one. The construction method comprises a bottom-layer bridge erecting procedure, an upper-layer bridge erecting procedure and a hole passing procedure of the bridge erecting machine, and the three procedures are circularly operated. The procurement