More details about rotary drilling tools

In our article “How many kinds of drilling tools for rotary drilling are there?”, we introduced the types of drilling tools and how they work. In this article, let’s know their structure and applications.

Drilling Bucket

Based on the bottom structure, the drilling bucket can be divided into following types:

- Soil layer double bottom double opening drill bucket

Suitable for silt, fine sand, silt, silty clay, clay, some types of soil soft rock, such as fully, strongly weathered and weathered mudstone, argillaceous sandstone, etc.

- Soil layer single bottom double opening drill bucket

This bucket has a similar function to a double-bottom sand fishing drill bucket. The advantage is that it has a side soil inlet and does not require back-drilling to close the bucket door, making it more efficient in drilling soil layers. The disadvantage is that it is lightweight. When used in some hard soil layers, especially when used with friction rods, it may slip and fail to penetrate, seriously affecting drilling efficiency. Suitable for sticky or pebbly loose soil.

- Rock double bottom double opening drill bucket

Suitable for pebbles, gravel layers, moderately weathered soil-like soft rock, such as weathered argillaceous sandstone, argillaceous conglomerate and harder rocks with higher degree of weathering, such as fully and strongly weathered granite, etc. When drilling hard rock, it is often necessary to use barrel drills and spiral drill bits.

- Rock double bottom single opening drill bucket

Compared with the double-bottom double-door drilling tool, it has a larger single-side soil inlet, which is more conducive to drilling in some formations, such as pebble formations with a particle size of less than 200mm. However, due to the asymmetric structure of the single door, there are higher requirements for design or production, otherwise the phenomenon of partial holes will easily occur. This drill bit is recommended for drilling pebble formations with small pile diameter ≤1.2m.

Based on the shape, the drilling bucket can be divided into Cone and Straight.

Based on the unlocking method, the drilling bucket can be divided into Automatic and Manual.

Core Barrel

Based on the drill teeth used, the core barrel can be divided into bullet teeth core barrel and roller teeth core barrel.

- Bullet teeth core barrel is suitable for circumferential cutting of moderately weathered sandstone with obvious layering (high probability of coring) and hard rock formations. In denser soil layers or some soft rock formations, when friction-type drill pipes cause slippage, you can try using a barrel drill.

- roller teeth core barrel is suitable for medium and light wind rock formations, hard rock formations, and ultra-hard bedrock formations.

Besides, there is the other double layer barrel drill:

It is suitable for drilling pebbles and boulders with a particle size of 200 to 500 mm. The double-layer barrel drill adopts a new drilling idea of "squeezing". That is, crushed and pebbles of different sizes are squeezed in the cylinder and brought out of the hole. During design, the diameter of the outer cylinder is designed based on the diameter of the pile hole, and the diameter of the inner cylinder is designed based on the average particle size of the pebbles. The inner cylinder is taller than the outer cylinder. In terms of drilling efficiency and drill tooth loss, it is obviously better than other drilling tools.

Drilling Auger

Based on the bottom structure, the drilling bucket can be divided into following types:

- Soil layer single head single screw straight auger

There is a lot of stagnant soil at the entrance and good guidance. Suitable for clay soil.

- Soil layer double-headed single screw straight auger

Lots of soil and good guidance. Suitable for frozen soil or pebbles with good cementability.

- Soil layer double-headed screw straight auger

Smooth drilling and good guidance. Suitable for clay with low water content or pebbles with good cementability.

- Rock single cone single spiral

Large soil inlet makes unloading soil convenient. Suitable for hard frozen soil, shale, large diameter pebbles.

- Rock biconical single spiral

Good guidance and good soil unloading. Suitable for hard frozen soil, large diameter pebbles or weathered bedrock.

- Rock double cone double spiral

Good guidance. Suitable for hard frozen soil, large diameter pebbles or weathered bedrock.

Centrifugal Bucket

The structure of the bottom cleaning drill is basically the same as that of the drill bucket, except that there are no teeth on the bottom plate and are replaced by scrapers.

The purpose of designing the split centrifugal drilling bucket was to solve the problem of difficulty in unloading slag in plastic formations with small holes. However, with the use of construction, it was found that the split drilling tool has a stronger drilling ability than the double bottom drilling tool. Therefore, the split drilling tool is not only used for construction. Open-body drilling tools can be used in plastic strata with small pile diameters, dense gravel layers, low-strength sedimentary rocks, fully/strongly weathered rock formations, etc., with pile diameters ranging from 0.6m to 1.5m.

Belling Bucket

Reaming piles can effectively increase the bearing capacity of pile foundations, so belling bucket came into being. Mechanical reaming bits are one of the more common types of reaming bits. They apply axial pressure downward through the drill pipe to expand the reaming fins and rotate the reaming wall through torque to meet the reaming design requirements.