Reasons and Prevention of Offset Hole Phenomenon of Rotary Drilling Rig

In the construction specification of rotary drilling rig, the allowable deviation of verticality is 1% degree, and the maximum allowable deviation range is about 1.7 meters for a pile length of 100 meters, and about 0.85 meters for a pile length of 50 meters. At present, many hole inspection equipment for pile driving engineering has adopted ultrasonic tester, which is very accurate for the inspection of pile length, pile diameter and verticality. If it exceeds the specification range, it will affect the quality of the hole and affect the construction progress.

1. Partial hole phenomenon:

1. Sharp partial hole: The sharp partial hole is generally caused by geology. Due to the weathering degree of the rock layer and the uneven distribution of the rock, the drill bucket is suddenly stuck when the main roll is lowered to a certain position in the hole, or the drill pipe suddenly deviates to a certain position. side, indicating a sudden deviation of a certain position in the hole.

2. Slow deviation: when the main roll is lowered, with the extension of the hole depth, the first section of drill pipe leans to the side of the casing and deviates from the center. It means that the hole is slowly deviated in one direction, and the closer the hole is, the more deviation.

3. Irregular deviation: With the lowering of the drill pipe, the first section of the drill pipe shakes left and right, or the irregular spiral deviation phenomenon in the hole can be directly observed when the dry hole is drilled. Rock formation, longitudinal deviation due to uneven force when the drill bucket is drilling.

2. Reasons for partial holes:

1. Geology: Geology is the main reason for partial holes. If the geology is all loess layers and clay layers, there will be no deviation in the holes. Most of them are caused by geological changes, and uneven distribution of weathered rocks and rocks, resulting in drilling during drilling. It is caused by the uneven force of the bucket.

2. Drill bucket: The main function of the drill bucket is cutting and drilling, but it also has the function of guiding and preventing deviation. The pilot tip in the center of the drill bucket has a positioning function, and at the same time, the pilot tip can change the drilling sequence, whether the number and angle of the drill teeth are consistent, and whether the heights of the side knives or guard strips on both sides of the drill body are consistent. The left and right forces are evenly applied to prevent deviation.

3. Operation: When there are rocks, boulders, pebbles, and weathered rock formations in the hole, it is necessary to control the floating and pressurizing methods. If drilling quickly, it will cause sharp deviation of the hole.

3. How to prevent:

1. Understand the geology: During the inspection of the project, through the geological report, core sampling, geographical environment, etc., to understand the geological situation in detail.

2. Drill bucket: Through actual verification, the auger bucket can prevent deviation better than the double bottom salvage bucket. The reason is that the drilling resistance of the auger bucket is small, and the pilot drilling method can effectively prevent the partial hole.

3. Optimize the drill bucket: optimize the drill bucket as much as possible, so that the drill bucket can reduce the drilling resistance, especially the center pilot tip has a positioning function, which can effectively prevent partial holes.

4. Steering drill bucket: A 2-meter-long protective tube that matches the hole diameter can be welded on the top of the auger bucket or double-bottom drill bucket, and guided drilling by lengthening the drill bucket can effectively prevent partial holes.

5. Operation: Controlling float, pressurization, rotation speed, and drilling speed can effectively reduce deviation.

6. Drilling method: Judging the current geological conditions by vibration and load, and changing the drilling method: such as cutting drilling, crushing drilling, toggle drilling and grinding drilling, by changing the drilling method, Can effectively prevent partial hole.