Rotary Drill Bits for Drilling Rigs

Rotary drilling rigs are one of the most commonly used machines in modern pile construction. Due to the varying geological conditions of each site, selecting the appropriate drill bit becomes a critical factor during pile driving. Here, we discuss how to choose the right rotary drill bit after assessing the site’s geological characteristics.

Different Types of Drill Bits

Double-Bottom Sand Bucket for Soil Layers: Suitable for mud, fine sand, silt, silty clay, clay, and some soft rock formations, such as fully or moderately weathered mudstone or siltstone. This is one of the most widely used drill bits in the industry.

Embedded Rock Double-Bottom Sand Bucket: Ideal for layers containing gravel or cobble, and for moderately weathered soft rock, such as siltstone with embedded gravel. It can also handle fully or highly weathered harder rocks, like granite. When drilling hard rock, it is often used in combination with barrel bits and spiral drill bits.

Barrel Drill Bit: Best suited for distinctly layered, moderately weathered sandstone, where core retrieval is likely, and for ring-cutting in hard rock layers. In high-density soil or soft rock formations where friction rods cause slippage, barrel bits may help.

Embedded Rock Spiral Drill Bit: Useful for breaking up boulders or hard rock within the borehole. For formations with cohesive soil or medium-dense gravel where double-bottom sand buckets cannot penetrate, spiral drill bits may be attempted.

Double-Layer Barrel Drill: Designed for drilling gravel or cobble layers with particle sizes between 200-500 mm. This bit uses a unique "compression" drilling method, compacting rocks inside the barrel before removing them. It has been widely adopted in domestic projects, with improved drilling efficiency and reduced wear on drill teeth.

Single-Bottom Sand Bucket for Soil Layers: Similar in function to the double-bottom sand bucket but has a side soil intake, eliminating the need to close the bucket door while reverse-drilling. It provides higher drilling efficiency in soil layers but may struggle with hard soil layers, especially when used with friction rods, where it might slip and fail to advance.

Soil Spiral Drill Bit: Suitable for small pile diameters and cohesive clay layers. Its maximum height can reach 4 meters, allowing for significant single-pass penetration and minimizing the common issues with debris removal in similar projects.

Single-Door Double-Bottom Bucket: Generally for bits with a diameter ≤ 1.2 m. Compared to double-door buckets, it has a larger single-sided intake, making it more effective for certain formations, like cobble layers under 200 mm. The asymmetrical design of the single-door bucket requires careful design to avoid borehole deviation. This bit is recommended for drilling cobble layers with small pile diameters ≤ 1.2 m.

Types of Drill Teeth and Their Applications

Drill teeth are the components of the rotary drilling system that make direct contact with the material, and their type, angle, and spacing are critical for drilling efficiency. High-quality drill teeth should be crack-free, durable, wear-resistant, and easy to install and remove.

There are four common types of drill teeth:

1. Bucket Teeth: Suitable for soil drilling, with sharp edges for fast cutting. Not suitable for gravel, rock, or other hard formations.

2. Bauer Teeth: Thicker and more robust than bucket teeth, making them harder to break. Suitable for large-diameter soil buckets and medium-small gravel or soft rock formations.

3. Pick Teeth: Designed for rock drilling, with a wear-resistant alloy tip that applies higher pressure to break up rock.

4. Tricone Teeth: Ideal for extremely hard rock, using a rolling mechanism to crush the rock. Its self-rotating design reduces vibrations during drilling, and multiple alloy cutting edges extend its service life.

   
   

These are the main types of rotary drill bits and drill teeth used in various geological conditions for pile construction. Understanding the geological characteristics of the construction site is essential to select the most appropriate drill bit for efficient and successful drilling.