Hole forming method for cast-in-situ bored pile

The invention relates to the technical field of bridge engineering, and discloses a hole forming method for a cast-in-situ bored pile. For a covering layer, a rotary drilling rig is assembled with a rotary drilling bucket for first drilling, and the construction efficiency is high; after entering rock, the rotary drilling rig is first assembled with a roller cone cylinder drill for secondary drilling, then a cutting pick cylinder drill is changed for third drilling, roller cone cylinder drills with different sizes are changed for step-by-step reaming, and at the stage, the problems of slow footage drilling, drill jamming, drill rod fracture and the like caused by insufficient torque after the rotary drilling rig enters the rock can be avoided; and after the reaming is in place, a percussion drill is changed to trim the hole shape of a primary pile hole, finally a mud circulating system is utilized to clear the formed pile hole, and it is ensured that the drilling slag at the bottom ofthe pile hole is thorough