Advances in Hydraulic and Water-Powered DTH Drilling Technology.

1. Advantages of Hydraulic Rock Drills

   ① High Hydraulic Pressure: Typically ranging from 10 to 25 MPa, with a trend toward higher limits. This is several to dozens of times higher than pneumatic pressure.

   ② High Output Power: Generally between 5 to 20 kW. Some models, such as the COP4050 by ATLAS and the HL2000 by TAMROCK, reach 40 kW, while the HL4000 achieves up to 70 kW.

   ③ Fast Drilling Speed: Usually achieves a drilling rate of 1–3 m/min.

   ④ High Efficiency: The efficiency of hydraulic rock drills themselves can reach 50%, and hydraulic pumps are more efficient than air compressors. Consequently, the overall energy utilization is significantly higher than that of pneumatic rock drill systems.

2. Disadvantages of Hydraulic Rock Drills

   ① Energy Transmission Loss: Since the rock drill is located at the top of the drill rod, energy transmission losses increase with greater hole depth, resulting in decreased drilling speed.

   ② High Drill Rod Wear: As the power of hydraulic rock drills increases, the stress on the drill rod also increases, leading to higher damage rates. Although technologies like Atlas Copco's casing drilling help reduce stress, they increase costs and fail to completely solve the problem, thereby limiting the drill's output power. For example, while the COP4050's power is rated at 40 kW, only 30 kW is used for deep-hole drilling to minimize stress on the equipment.

   ③Borehole Deviation: Drill rods endure both impact forces and torque, leading to bending and deformation, which reduces borehole accuracy.

3. Advantages of Down-the-Hole (DTH) Drills

   ① No Energy Transmission Loss: The hammer directly impacts the drill bit, eliminating the need for impact energy transfer via the drill rod, ensuring consistent drilling speed regardless of depth.

   ② Straight Boreholes: The drill rod has high rigidity, is not subjected to impact forces, and transmits only torque with minimal axial pressure. This prevents bending and deformation, ensuring straight and smooth boreholes. Dth Drills perform better in fractured formations, inclined strata, or variable rock hardness.

   ③ Efficient Debris Removal: The power medium doubles as a flushing medium, thoroughly cleaning the borehole and avoiding over-drilling.

   ④ Low Noise: Since impact occurs at the borehole bottom, noise is significantly lower than top-hammer drills.

   ⑤ Broad Applicability: Except for very soft formations, DTH drills operate optimally in all rock types, surpassing top-hammer rock drills in achievable borehole diameter and depth.

   Given these advantages, DTH drilling is widely regarded as the best choice, with 90% of British quarries adopting this method.

4. Disadvantages of Pneumatic DTH Drills

   ① Low Pressure and Power: The primary drawback of pneumatic DTH drills is their low air pressure and output power, leading to slower drilling speeds. While advancements have raised air pressure to 2.5 MPa, this is still far below the hydraulic pressure of rock drills. Moreover, high-pressure air compressors are expensive, require high-power drives, produce more noise, and lose efficiency significantly in high-altitude areas.

   ② Low Energy Utilization Efficiency: Pneumatic DTH drills consume three times more energy per meter drilled than hydraulic rock drills.

5. Applications of Hydraulic DTH Hammers

   To integrate the advantages of hydraulic rock drills (high pressure and efficiency) and DTH drills (straight boreholes), Germany's Hausherr developed the “Rapid Hydraulic DTH Drill” in the early 1990s. Both its rotation and impact mechanisms are hydraulically driven. The hammer features two oil lines for supply and return. Rapid drills are available in three diameters: 90 mm, 115 mm, and 150 mm, suitable for boreholes with diameters of 100–125 mm, 127–156 mm, and 168–230 mm, respectively.

   A comparative test between the Rapid and Hausherr's HBM80S pneumatic DTH drill showed that, for identical borehole diameters (125 mm) and depths (36 m), the Rapid exhibited significant economic advantages with lower engine power, fuel consumption, and lubrication oil consumption ratios of 0.46, 0.46, and 0.47, respectively.

6. Applications of Hydraulic Water-Powered Hammers

   Sweden's LKAB and its subsidiary G-Drill developed the “Wassara Water-Powered dth hammer” in the late 1980s. Using filtered mine water as the medium, it operates at a pressure of 18–20 MPa and flow rates of 200–300 L/min. With average drilling speeds of 850 mm/min, it outperforms pneumatic hammers (typically 320 mm/min).

   The Wassara hammer has demonstrated exceptional performance, such as reducing borehole deviation by half and increasing productivity by 86% in LKAB mines. Applications include subway grouting in New York and geothermal drilling in Switzerland, where it completed a 599.8 m borehole in 5 days, compared to 3 weeks with traditional rotary drills.

7. Comparison: Hydraulic Water-Powered vs. Hydraulic Fluid-Driven Hammers

   Water-Powered Hammers: Utilize static water pressure, achieving higher efficiency and drilling speeds, suitable for mining applications.

   Fluid-Driven Hammers: Use dynamic water pressure and are generally limited to geological drilling with lower pressures (0.5–4 MPa) and efficiency (<30%).

8. Conclusion

   Hydraulic and water-powered DTH hammers combine the advantages of top-hammer hydraulic drills and pneumatic DTH hammers, offering low energy consumption, fast drilling speeds, and straight boreholes. The unified medium for power and flushing makes water-powered hammers more promising for future development.