Construction method and auxiliary device for cutting steel pipe pile under riverbed

The invention discloses a construction method and an auxiliary device for cutting a steel pipe pile under a riverbed, and relates to the technical field of underwater engineering construction.The construction method comprises the steps that the outer diameter of the steel pipe pile to be cut and the height from the water surface to the riverbed are measured; a sleeve is manufactured, the sleeve comprises an annular steel pipe section on the upper half portion and a conical steel pipe section on the lower half portion, and an open hole used for sleeving the steel pipe pile is formed in the bottom of the conical steel pipe section; the length of the annular steel pipe section is larger than the height from the water surface to the riverbed, and the gap between the radius of the annular steel pipe section and the radius of the steel pipe pile is not smaller than 0.6 m. And a to-be-cut steel pipe pile is sleeved with the bottom opening of the sleeve from top to bottom, so that the conical steel pipe section is cu