Analysis of Slippage in Mud Layers during Rotary Drilling
2013-07-08
505
0人评论
1. Bucket Bottom Closure
When using a friction bar rotary drilling rig to drill into the mud layer of a water pile, pay attention to the drilling depth per bucket. If the single-bucket drilling depth is too deep, the drilling bucket is already full of soil. The soil cut by continued drilling has nowhere to accommodate and accumulates at the slag inlet of the drilling bucket and in front of the bucket teeth. When the accumulated soil reaches a certain amount, a large block of soil forms in front of the bucket teeth, equal in height to the bucket teeth and integrated with them. At this time, the bucket teeth have lost their cutting function. Under the lubrication of mud or water, the drilling bucket cannot continue drilling. Therefore, when reversing to close the bucket bottom, there is no resistance at the bucket bottom, so the bucket bottom will rotate together with the drilling bucket and cannot be closed.
2. Slag Falling Out
After reversing, the main winch is lifted. When the drilling bucket is lifted in mud or water, due to the certain resistance of the mud or water, this resistance generates a downward force on the slag inside the drilling bucket. Because the drilling barrel of the bucket is conical, excessive rotary drilling speed causes the slag inside the bucket to be insufficiently compacted, and rapid lifting of the main winch, etc., cause the slag in the bucket to fall out. Therefore, it is not that the slag will fall out every time the bucket bottom is not closed…
3. Slippage Phenomenon
At this time, the fallen slag has lost the original integrity of solid soil. Therefore, after the second drilling, the tooth tips directly insert into the slag, and the bottom plate of the drilling bucket directly presses on the slag. As the drilling bucket rotates and drills, the uneven and gaps of the fallen slag are completely compacted. When the slag cannot be compressed further, the plane of the bottom plate is supported by the slag, and the bucket teeth repeatedly rotate in the already scratched grooves. At this time, three layers are formed: the first layer is the repeatedly rotating drilling bucket, the second layer is the fallen slag, i.e., the interlayer, and the third layer is the uncut solid soil. Since the diameter of the drilling bucket matches the hole, and the drill rod rotates without resistance → no reaction force → no friction → no applied pressure, the bottom plate and the fallen slag, under the lubrication of water or mud, exhibit slippage.
4. Preventing Slippage
The slippage phenomenon can be overcome. First, combine with the single-bucket drilling depth on the display. Although the drilling resistance in the mud layer is small, as the slag inside the drilling bucket increases, resistance is generated at the slag inlet, thereby increasing the drilling resistance. The sound of the planetary reducer on the power head changes with the resistance, so listening to the sound of the power head can judge the drilling amount. When the drilling resistance increases, the rotation speed of the power head also decreases, so the drilling amount can also be judged by the drill rod rotation speed. If the geological changes are not significant, the drilling time and depth per bucket should be kept within a certain range. The single-bucket drilling depth in the mud layer should be within 0.5 to 0.6 meters. When reversing to close the bucket bottom, try to do so when there is load during drilling. At this time, the bucket bottom has a certain resistance, thereby preventing the bucket bottom from rotating together with the drilling barrel.
5. Handling Slippage
[1] Even if slippage occurs, it can be handled. After the second drilling, first determine the thickness of the fallen slag through the data on the display, and then check the softness and hardness of the fallen geology. If a lot of soil has fallen and it is hard clay, replace with a drilling bucket slightly smaller than the pile diameter to solve the slippage. Because there is a larger gap between the small-diameter drilling bucket and the hole wall, the fallen soil is squeezed to the side through the gap between the drilling bucket and the hole wall under the weight of the drill rod and drilling bucket and the applied pressure. The small-diameter drilling bucket can drill normally when it contacts the solid soil. After the small bucket is lifted, the virtual soil squeezed to the side falls into the small-diameter hole. The slag that does not fall into the small hole is squeezed into the small hole by the large-diameter drilling bucket during the second drilling, so that the large-diameter drilling bucket can drill normally.
[2] If the fallen slag is soft mud with good compressibility, there is no need to change the drilling bucket. Repeatedly operate the pressure and the power head to reverse and forward rotate. Because there is a gap between the power head and the drill rod, and also between each section of the drill rod, although drilling slips at this time, the weight of the drill rod and drilling bucket itself has resistance. Therefore, quickly reversing and forward rotating the drill rod can generate impact force through the gaps. The impact force encounters the weight of the drill rod and drilling bucket itself and generates resistance. With resistance, there is reaction force; with reaction force, there is friction. At this time, the applied pressure can be instantly transmitted to the virtual soil of the interlayer to compress the fallen slag, allowing the slag to be squeezed up through the gap between the drilling bucket and the hole wall, and part of it to enter the drilling bucket, until the bucket teeth contact the solid soil and normal drilling is achieved. Remember, when reversing and forward rotating, apply pressure first to transmit the applied pressure instantly.
评论 （0）