Views: 0 Author: Mick Chan Publish Time: 2025-10-27 Origin: Site
As the core equipment in modern pile foundation engineering, the construction efficiency and borehole quality of rotary drilling rigs directly depend on the operator's precise control of key parameters. Among these, rotation speed and torque are the two soul parameters. They are not fixed but must be flexibly adjusted according to the "temper" of the stratigraphic geological conditions. Understanding the principles behind this is the key to achieving efficient, high-quality, and safe construction.
Rotation Speed: Refers to the rotational speed of the drill pipe, usually measured in revolutions per minute (rpm). It is primarily responsible for cutting and fracturing soil and rock, and guiding the cuttings into the drill bucket. The level of rotation speed directly affects drilling efficiency and tool wear.
Torque: Refers to the torsional moment generated when the drill pipe rotates, usually measured in kilonewton-meters (kN·m). It is primarily responsible for overcoming resistance, driving the drill bit to cut and fracture the formation, and serves as the fundamental guarantee for providing powerful force, especially in hard or complex strata.
Simply put, torque is the "strength," determining whether it can drill; rotation speed is the "pace," determining how fast it drills. The two must be perfectly coordinated to achieve maximum effectiveness.
Different strata have distinct characteristics, and the "approach" of the rotary drilling rig must change accordingly.
1. Soft Soil Layers (Clay, Silt, Fill, etc.)
Geological Characteristics: Low resistance, good self-stability, prone to adhering to the inside of the drill bucket.
Rotation Speed and Torque Adjustment Strategy:
High Speed, Low Torque. Such formations are easy to cut and do not require excessive "strength." Higher rotation speeds (e.g., 20-30 rpm) should be used to achieve rapid drilling and improve efficiency.
Key Point: In cohesive soil layers, excessively high speed can easily cause "bit balling" (where the drill bucket gets clogged with mud, making discharge difficult). In this case, appropriately reduce the speed and choose open-type drill buckets or friction-type drill pipes to facilitate soil discharge.
2. Sand Layers, Gravel Layers (Loose to Medium Dense)
Geological Characteristics: Loose structure, prone to collapse and fluid loss, unstable resistance during drilling, significant vibration.
Rotation Speed and Torque Adjustment Strategy:
Medium-Low Speed, Medium-High Torque. To prevent high speed from aggravating wall disturbance and collapse, the rotation speed should be appropriately reduced (e.g., 10-20 rpm) to maintain stable drilling. Meanwhile, to cope with local obstacles like gravel, stable and sufficient torque is needed to ensure smooth cutting and penetration.
Key Operation: Must be combined with mud wall protection, and use drill buckets with baffles to prevent sand and gravel from falling. Operation must be smooth, avoiding sudden loading or lifting of the drill.
3. Highly Weathered, Moderately Weathered Rock Layers
Geological Characteristics: High rock strength, but partially fractured, requiring strong cutting and fracturing capabilities.
Rotation Speed and Torque Adjustment Strategy:
Low Speed, High Torque. This is a typical "brute force" working condition. Torque must be adjusted to a high level to ensure sufficient power to break the rock. The rotation speed should be reduced (e.g., 5-15 rpm) to minimize severe impact between the drill teeth and the rock, protect the drilling tools, and prevent "slipping" and borehole deviation.
Tool Selection: Must use rock drilling buckets (e.g., pick-type bits, roller cone bits), utilizing high torque for effective grinding and fracturing.
4. Hard Bedrock, Slightly Weathered Rock Layers
Geological Characteristics: Excellent rock integrity, extremely high strength, huge drilling resistance.
Rotation Speed and Torque Adjustment Strategy:
Lowest Speed, Maximum Torque. At this point, the rotary drilling rig should focus on maximum torque output, with the speed reduced to the minimum range allowed by the equipment (e.g., 3-8 rpm), performing a "slow and steady" grinding process. Excessively high speed will not improve efficiency but will instead rapidly wear down the drill teeth and even damage the drill pipe.
Pressure Control: Requires appropriate down pressure (using a Kelly bar) to achieve dual rock breaking through "torque + pressure".
"Listen and Observe": Experienced operators judge formation changes by listening to the engine sound, watching the instrument panel (torque, pressure readings), and feeling the vibration of the entire machine. A sudden increase in the torque meter reading indicates encountering a hard layer; severe shaking of the machine may indicate boulders or gravel layers.
"Stable First, Then Fast, Dynamic Adjustment": When lowering the drill, start with low speed and torque for probing, then increase speed and force according to the situation after entering a stable formation. Throughout the entire drilling process, parameters change dynamically and are never set once and for all.
The Drilling Tool is the Executor: The adjustment of speed and torque must match the type of drill bucket. Using a bucket designed for cutting clay to drill rock is futile no matter how high the parameters are.
Protecting the Equipment is the Bottom Line: Avoid applying huge torque suddenly at high speeds. This kind of "ramming" operation can easily cause irreversible damage to key components such as the power head and drill pipe.
Conclusion
The operation of rotary drilling rigs is an art combining science and experience. Adjusting rotation speed and torque is essentially a precise response to the unknown world underground. Only by deeply understanding formation characteristics, thoroughly mastering equipment performance, and continuously summarizing practical experience can one achieve "man-machine integration," allowing the rotary drilling rig to perform with ease and high efficiency on different geological stages. Remember, there are no immutable "golden parameters," only "construction wisdom" that adapts to the situation.
