Follow-pipe drilling is divided into eccentric follow-pipe and concentric follow-pipe. The process principles of the two are different.

　　(1) Working principle of eccentric drill pipe.

　　During normal drilling, the eccentric drill is driven to drill by the vibration and impact of the impactor. When drilling, due to centrifugal force and friction, the eccentric deflects outward to achieve the purpose of expanding the hole diameter. Then, the casing is driven by the impact of the drill pipe stabilizer to follow up, and the rock powder generated during the drilling process is blown out from the hole through the key groove on the drill pipe stabilizer. After drilling, by reversing the direction, the eccentric is folded and the casing is lifted out, leaving the casing in the hole to protect the wall to form a hole. When the well depth is less than 40m and there are no large boulders in the formation, pipe eccentric drilling should be used.

　　(2) Working principle of concentric pipe drilling.

　　The center bit and the concentric sleeve sleeved outside the center bit are used to impact and crush the rock to form a hole, and the sleeve is brought into the hole by the reaming effect of the concentric sleeve. The concentric sleeve is provided with a keyway. After reaching the bedrock, the center bit reverses and exits through the concentric casing. The concentric follower tube can better solve the problems of stuck and drilled boulders caused by complex geological conditions during eccentric follower drilling, which is more conducive to construction operations and improves drilling efficiency. When the well depth exceeds 40 meters and there are many boulders in the formation, pipe concentric drilling should be used.

　　After following the pipe, drill to the designed hole depth with a conventional drill.