High-speed railway bridge variable-pile-diameter pile foundation construction method under spoil disposal site condition

The invention discloses a construction method for a variable-pile-diameter pile foundation of a high-speed railway bridge. According to a design scheme, a total station is used for measuring, lofting and marking, the depth of a waste slag layer is explored, the elevation of a hole opening is measured, and a drilling machine is installed; a first drill bit drills holes in the waste slag layer; after drilling of the waste slag layer is completed, a permanent pile casing is buried in the waste slag layer, and a second drill bit is used for drilling to the designed pile bottom elevation along the center line of the permanent pile casing; and hole cleaning: hoisting the reinforcement cage, and pouring concrete after secondary hole cleaning. According to the construction method, the pile diameter of the pile foundation is enlarged in the slag discarding layer range, full-pile-casing construction is adopted, the outer side of a permanent pile casing is coated with a resistance reducing material to reduce the lowerin