Rapid construction method for large-diameter pile foundation in deepwater karst area

The invention relates to the field of pile foundation construction, in particular to a rapid construction method for a large-diameter pile foundation in a deepwater karst area. A rotary excavating drill bit assembly is composed of a first drill bit body, a second drill bit body and a rotary connecting piece, the first drill bit body is fixedly connected to the lower end of a steel casing, and the second drill bit body is fixedly connected with the rotary connecting piece; the first drill bit body is of a cylindrical structure with a cutting edge at the end, the second drill bit body is arranged in the first drill bit body, a sliding rail and a lifting sliding block arranged on the sliding rail in a sliding mode are arranged on the rotary drilling rig, the rotary connecting piece is rotationally connected to the lifting sliding block, and a linkage assembly is arranged between the first drill bit body and the second drill bit body. The first drill bit body and the second drill bit body can synchronously rotate