Pile foundation construction method for sectioning pile casing as required in vertical string-shaped karst cave area

The invention discloses a pile foundation construction method for sectioning a pile casing according to needs in a vertical string-shaped karst cave area, which is suitable for the technical field of bridge building pile foundation construction and comprises the steps of construction preparation, in-place of a percussion drill pile machine, burying of a trepanning pile casing, sectioning follow-up construction of an inner pile casing protection net according to needs, manufacturing and mounting of a reinforcement cage and pouring of underwater concrete. The method specifically comprises the following steps that the type of a karst cave is identified, follow-up of the inner pile casing and the protection net is conducted, a plurality of inner pile casings are arranged in a segmented mode as needed according to the type of the corresponding karst cave below a main pier pile foundation, a protection net cylinder is connected between every two inner pile casings in a lap joint mode, and the construction difficult