Bucket drilling is a rotary drilling method that uses a cylindrical bucket with cutting blades or teeth to excavate soil and rock, which is then lifted to the surface, emptied, and reinserted to drill deeper.
Bucket drilling, although not as popular as churn drilling, has important applications in placer deposit evaluation. Under ideal conditions, this technique is relatively fast and provides large samples. In this system, a standard rotary drill is equipped with a special “bucket” bit consisting of a 30- to 48-in-diam cylinder, 3 to 4 ft long.
The bit is driven down through the deposit, using the rotational force of the drill, until the cylinder is full. As the bit is withdrawn, a mechanism closes off the bottom of the bit retaining the sample. The process is then repeated until the desired depth is reached.
Bucket drills perform best in sands, soils, pebbles, and clays. Progress is slow, and sometimes impossible, in ground containing boulders, cemented gravel layers, and bedrock. The size of the bit tends to disperse drilling force over a large area, thereby reducing the effective penetration rate.
For this reason, the bucket drill quickly becomes inefficient in hard or compact material. Problems are also encountered in saturated ground, where water often washes away a portion of the sample as the bit is withdrawn.
Bucket drilling extracts a much larger sample than other drilling methods. Consequently, the influence of the bit on compaction and expansion of material is reduced.
