Disc drilling, also known as rotary drilling, is a common drilling method used in construction, mining, and environmental exploration. It involves using a rotating disc or roller with cutting teeth to penetrate and break up soil and rock. Compared to other drilling methods like percussion and cable tool drilling, disc drilling is generally faster and more efficient. However, there are some safety concerns associated with disc drills that need to be considered. In this article, we will look at how disc drills work, their advantages and disadvantages, safety hazards, and best practices for safe disc drill operation.
How Does a Disc Drill Work?
A disc drill consists of a rotating disc or roller covered with hardened steel teeth or tungsten carbide inserts. The disc is mounted on a hydraulic motor which rotates the disc at speeds ranging from 300 to 1200 RPM. The weight of the drill is applied behind the disc using hydraulic cylinders and the downward pressure forces the rotating disc to penetrate the surface. As the teeth on the disc encounter the material being drilled, they chip and scrape away pieces of it. The cutting action is continuous as new portions of the disc come in contact with the bottom of the hole.
Fluid is pumped down the center of the drill pipe and exits at the disc face. This fluid, usually water or drilling mud, helps to cool the disc, flush away cuttings, and stabilize the hole. The fluid and cuttings rise back up the annular space around the drill pipe and are collected. Larger rigs may utilize a dust collection system to contain cuttings and dust generated during drilling.
Advantages of Disc Drilling
Some key advantages of disc drills over other drilling methods include:
– High penetration rates – Disc drills can drill through hard materials much faster than cable tool or percussion methods. Penetration rates of up to 300 feet per hour can be achieved.
– Continuous operation – The rotation of the disc allows for continuous drilling without the need to constantly trip in and out of the hole. This results in faster overall drilling.
– Directional control – The rotation of the disc improves directional control compared to percussion methods. The angle of the hole can be better maintained.
– Less deviation – Holes drilled with a disc drill tend to be straighter with less deviation than those drilled with cable tools.
– No Jarring – The smooth, rotational action reduces vibration, noise, and jarring compared to impact drilling methods. This is safer and less disturbing to surrounding structures.
– Versatility – Disc rigs can be used for both core and full-hole drilling and can be applied across a wide range of geological conditions.
Disadvantages of Disc Drilling
Some disadvantages and limitations of disc drills include:
– High equipment costs – Disc drilling rigs represent a much higher capital investment than cable tool or percussion rigs.
– Larger footprint – Disc drills have a larger operational footprint and require more setup space than more compact percussion rigs.
– Less suitable for hard rock – In very hard rock conditions, disc penetration rates may not be significantly faster than cable tool drilling.
– More maintenance – The hydraulic systems and disc components require frequent inspection and maintenance.
– Core retrieval limitations – When used for core drilling, intact core recovery may be limited compared to diamond core drilling.
– Hole size limitations – Disc drilling is typically limited to smaller diameter holes, usually less than 16 inches. Larger holes require impractically large discs.
Disc Drill Safety Hazards
While disc drilling provides major productivity advantages, the operation of these powerful rigs does present some important safety considerations. Some of the potential hazards include:
Rotating Equipment
The high-speed rotation of the disc, drive components, and drill string presents risks of entanglement and being caught by moving parts. Fingers, hands, loose clothing, or tools can easily get caught in the spinning components. Proper precautions are essential around the rig.
Ejected Materials
The fast drilling action can eject rock fragments, dust, and debris from the hole with considerable force. This can injure eyes and bodies if workers are not adequately shielded.
Buried Utilities
Damage and contact with buried electric, gas, water, or sewer lines can occur if locations are not properly identified before drilling. This can lead to injury and disruption of vital services.
Downhole Equipment Failures
If a disc or drill string gets lodged downhole during drilling, attempts to recover it can lead to breakage and sudden, uncontrolled movements at the surface.
Drill Control
Loss of control while operating the rig controls can result in equipment damage and worker injuries. This hazard is amplified when working on uneven or unstable ground.
Noise
Disc drills generate very high noise levels, requiring proper hearing protection to prevent permanent hearing damage with prolonged exposure.
Dust
Drilling can produce large quantities of dust containing respirable silica. This requires dust suppression and PPE to prevent respiratory health issues.
Disc Drill Safety Best Practices
To mitigate disc drilling hazards, certain safety precautions and work practices should always be followed:
Equipment Inspection & Maintenance
Routine inspection and preventive maintenance of the rig and its components is critical. This includes checking the disc, drill stem, hydraulics, lubrication levels, controls, and safety devices. A maintenance log should be kept.
Work Site Preparation
The work area should be cleared of obstructions and assessed for buried utilities and underground voids. Overhead lines must also be noted. Uneven surfaces present tripping hazards.
Guarding
All moving components like the disc, drive shaft, and pulleys must be guarded to prevent contact. Guards must be kept in place during operation. The work platform should have railings.
PPE
Workers must wear eye and face protection, hard hats, steel toe boots, hearing protection, and other applicable PPE. Dust masks should be used when appropriate.
Proper Rig Setup
The rig should be leveled and stabilized on footing pads or cribbing. Guy wires or anchors may be required. The work platform must provide safe access to drilling components.
Drill Control & Monitoring
Only trained operators should control the rig. The disc engagement and drill feed should have slow, controlled activation. Two workers should monitor the rig during drilling.
Downhole Monitoring
Downhole conditions should be continually assessed by monitoring the return flow rate, color, and monitoring the drill stem torque and advancement.
Securing the Site
The work zone around the rig should be isolated using barriers and marked with warning signs. Spotters should control vehicle traffic around the rig.
Dust & Noise Control
Dust suppression using water or collectors should be used. Hearing protection must be enforced. Rotating the work crew can limit noise exposure.
Proper Drill Stem Handling
Drill pipe should be properly secured in place during assembly, disassembly, and when stored in the pipe racks. Use material handling equipment when necessary.
Conclusion
Disc drilling provides an effective means of quickly penetrating through soil and rock. However, the responsible operation of these powerful rigs requires emphasis on safety. With proper precautions like worker training, safe setup, equipment maintenance, and safe work practices, disc drilling hazards can be mitigated. While the high-torque disc and drilling operation present risks if mishandled, following the safety best practices outlined above can allow disc drills to be used productively with minimal risks to workers. With oversight and attention to safety detail, disc drill operations can maintain both good productivity and safety.
| Disc Drill Advantages | Disc Drill Disadvantages |
|---|---|
| High penetration rates | High equipment costs |
| Continuous operation | Larger footprint |
| Directional control | Less suitable for hard rock |
| Less deviation | More maintenance |
| No jarring | Core retrieval limitations |
| Versatility | Hole size limitations |
| Disc Drill Safety Hazards |
|---|
| Rotating equipment |
| Ejected materials |
| Buried utilities |
| Downhole equipment failures |
| Drill control |
| Noise |
| Dust |
| Disc Drill Safety Best Practices |
|---|
| Equipment inspection & maintenance |
| Work site preparation |
| Guarding |
| PPE |
| Proper rig setup |
| Drill control & monitoring |
| Downhole monitoring |
| Securing the site |
| Dust & noise control |
| Proper drill stem handling |