Geotechnical drilling is a crucial part of soil and rock investigation for construction projects such as buildings, bridges, dams, and roads. One of the most important components in this process is the drill bit, which serves as the cutting tool that penetrates soil and rock layers.
Choosing the right type of geotechnical drilling bit is essential to ensure drilling efficiency, safety, and the accuracy of the collected data. Below, we classify the most common types of drilling bits used in geotechnical exploration, grouped by their functions and materials.
Drill Bits Based on Function
Drag Bit
Description:
Drag bits are designed with sharp steel blades shaped like wings, allowing them to scrape soft material as they rotate.
Applications:
Suitable for clay, sand, silt, and very soft rock.
Best used at high rotation speeds with low pressure.
Advantages:
Low cost.
Easy to replace and operate.
Saw Tooth / Jagged Tooth Drill Bit
Description:
The Saw Tooth (or Jagged Tooth) drill bit features serrated teeth at its cutting edge, resembling a saw blade. These teeth make the bit more aggressive in cutting through tough formations.
Applications:
Hard igneous rocks such as basalt and granite.
Interbedded formations with alternating hard-soft layers.
Abrasive formations that quickly dull standard bits.
Commonly used in geotechnical, mining, and oil & gas drilling.
Advantages:
Faster penetration in hard or mixed formations.
More wear-resistant in abrasive conditions.
Effective at creating micro-fractures for efficient rock breaking.
Disadvantages:
Less stable, prone to vibration and hole deviation.
Produces rougher boreholes compared to smoother bits.
Shorter lifespan if used in soft formations.
Higher cost due to specialized design.
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Tricone Bit
Description:
This bit consists of three independently rotating cones, each equipped with steel teeth or tungsten carbide inserts.
Applications:
Medium to hard formations such as sandstone, shale, and limestone.
Available in both milled-tooth and insert types.
Advantages:
Versatile across a wide range of rock conditions.
Durable and reliable for long drilling operations.
Core Bit
Description:
Core bits are designed to collect cylindrical samples (cores) of soil or rock for laboratory analysis. They may be made from diamond, PDC, or tungsten carbide.
Applications:
Widely used in exploration drilling and geotechnical investigations.
Advantages:
Provides direct geological samples.
Enables accurate strength and structural analysis.
Drill Bits Based on Material
Diamond Bit
Description:
Diamond bits are manufactured using industrial diamond particles bonded to the bit head with a metal matrix.
Applications:
Hard rock formations such as granite, basalt, and metamorphic rocks.
Commonly used in core drilling to obtain intact samples.
Advantages:
High drilling precision.
Long service life when used on suitable formations.
PDC Bit (Polycrystalline Diamond Compact)
Description:
PDC bits use synthetic diamond cutters (PDC cutters) attached to the bit body.
Applications:
Effective for medium to hard formations like shale and soft igneous rocks.
Ideal for high-speed, low-pressure drilling.
Advantages:
High productivity.
Longer lifespan compared to drag bits.
Tungsten Carbide Bit
Description:
Made from a blend of hard metals, tungsten carbide bits are often used in tricone or core bit designs.
Applications:
Medium-hard and abrasive rock formations.
Suitable for heterogeneous geological layers.
Advantages:
Strong and durable.
More affordable compared to diamond bits.
In geotechnical drilling, selecting the right drill bit for the geological conditions is essential to ensure efficient drilling, safe operations, and high-quality data. Factors such as soil and rock type, depth, drilling objectives, and operational costs must all be considered when choosing a bit.
With the correct selection, geotechnical projects can be completed faster, safer, and more cost-effectively. The accuracy of the samples and data collected ultimately depends on using the right geotechnical drilling bit for the job.