The borewell drilling procedure using a hammer drill, specifically the Down-the-Hole (DTH) hammer drilling method, is one of the most common techniques for drilling borewells, especially in hard rock areas. Here’s a step-by-step guide to the borewell drilling procedure using a hammer drill:
1. Site Selection and Survey
- Hydrogeological Survey: Before drilling begins, it’s essential to conduct a survey to identify the most suitable location for the borewell. A hydrogeologist or water diviner can help determine the best spot based on geological formations and the water table.
- Obtain Necessary Permits: In many areas, drilling borewells requires permission from local authorities. Ensure all necessary permits are in place before starting the drilling process.
2. Setting Up the Drilling Rig
- Position the Rig: The DTH drilling rig is brought to the site, usually mounted on a truck or trailer. The rig is positioned precisely at the identified drilling location.
- Stabilize the Rig: Stabilize the drilling rig by lowering its support legs or jacks to ensure it is level and secure for drilling.
3. Initial Drilling (Casing Pipe Installation)
- Shallow Drilling: Initially, drilling is done to create a shallow hole that can accommodate the casing pipe. This is important to protect the borehole from collapsing and to prevent loose soil from falling into the well.
- Casing Installation: A metal or PVC casing pipe is installed into the shallow hole to maintain the structure of the borehole. This pipe acts as a protective layer until solid rock is reached, at which point the casing is no longer needed.
4. DTH Hammer Drilling (Rock Drilling)
- Starting the DTH Hammer: Once the borehole reaches solid rock, the DTH hammer drill comes into play. The drill bit is attached to the end of the drill string, and compressed air is pumped through the drill pipes.
- Drilling Process: The DTH hammer uses a combination of rotational motion and percussive action to break through hard rock. The hammer mechanism delivers rapid blows to the drill bit, which crushes the rock while rotating at the same time.
- Compressed Air: High-pressure compressed air is used to operate the hammer. This air also serves to blow out rock cuttings and debris from the borehole, keeping it clean and ensuring efficient drilling.
- Drill Bit: The drill bit breaks the rock into small particles, which are flushed to the surface by the compressed air.
- Adding Drill Pipes: As the drilling progresses, more drill pipes are added to the drill string to reach deeper depths.
5. Monitoring the Drilling Progress
- Depth Measurement: The drilling operator monitors the depth of the borewell constantly. Depth markers on the drill pipes help determine how deep the well is progressing.
- Water Yield Testing: Once the water table is reached or if any water-bearing formation is encountered, the flow rate and quality of water are checked. The driller pauses to measure the water yield at various depths.
- Drilling Beyond the Water Table: In many cases, drilling is continued beyond the first encounter with water to tap into deeper and more abundant aquifers.
6. Flushing the Borehole
- Removing Debris: Throughout the drilling process, rock cuttings and debris are continuously flushed out of the borehole by the compressed air. Once drilling is complete, the borehole is thoroughly flushed to ensure all debris is removed.
- Clean Water Flow: The flushing process continues until clean water starts flowing from the borehole, indicating that no more drilling debris is present.
7. Final Casing Installation
- Additional Casing: If necessary, additional casing is installed deeper into the borewell to protect the walls of the borehole and prevent collapse. This casing typically stops at the water-bearing rock layers.
- Slotted Casing Pipes: In some cases, slotted or perforated pipes are used to allow water to enter the borehole from the surrounding aquifers while keeping out debris and sand.
8. Gravel Packing
- Gravel Packing Around the Casing: Gravel or coarse sand may be poured around the slotted casing pipe to prevent fine particles from entering the well. This gravel pack acts as a filter, allowing clean water to flow while blocking sand and silt.
9. Installation of Submersible Pump
- Pump Selection: Once the borewell is drilled and the casing is in place, a submersible pump is installed to lift water from the borewell. The depth of the pump is determined based on the water table level.
- Power Connection: The pump is connected to a power supply, and the control panel for the pump is set up.
10. Well Testing and Finalizing
- Test Pumping: After installation, the borewell is tested by running the pump to check the yield, flow rate, and quality of the water.
- Water Quality Testing: It is important to test the water quality to ensure it is suitable for drinking or irrigation purposes.
- Well Sealing: Once testing is complete, the top of the borewell is sealed to prevent surface contaminants from entering the well.
11. Well Maintenance
- Regular maintenance is necessary to ensure long-term water flow and quality. Periodic flushing and cleaning of the well and pump will help maintain performance.
Equipment Used in DTH Hammer Drilling
- DTH Hammer: A pneumatically powered hammer attached to the drill string. It delivers rapid impacts to the drill bit to crush hard rock.
- Drill Bit: The bit used at the bottom of the hammer to break through soil and rock.
- Air Compressor: A high-powered compressor that supplies air to operate the hammer and clean out the debris from the borehole.
- Drill Pipes: Hollow pipes that transmit compressed air and connect the hammer to the drilling rig.
- Casing Pipes: Metal or PVC pipes used to stabilize the borehole and prevent collapse.
Advantages of Using a Hammer Drill for Borewell Drilling
- Effective in Hard Rock: DTH hammer drills are highly effective in penetrating hard rock layers, which is crucial for borewell drilling in rocky terrains.
- Fast and Efficient: The percussive action of the hammer speeds up the drilling process, especially in solid rock formations.
- Clean Borehole: Compressed air efficiently removes debris from the borehole, reducing the risk of clogging and ensuring a smooth operation.
By following this procedure, the DTH hammer drilling method ensures effective and efficient borewell drilling, especially in areas with hard rock formations.