The bucket rig is a form of the rotary drill rig. It uses mechanical or hydraulic drive to rotate a Kelly which is attached to the bucket. This type of rig will normally utilize a square friction type or round locking type Kelly with three or four telescoping sections which can extend to 100ft or more. Bucket rigs may be equipped to drill holes from 10 to 60 inches in diameter. Bucket drilling uses a cylindrical bucket with cutting blades or teeth mounted on a hinged bottom to repeatedly cut and lift sediments from the borehole.
To drill, the bucket is rotated to allow the bottom of the cutting teeth to fill the bucket. When the bucket is full, it is raised by cable. Flaps at the bottom of the bucket will close to keep the soils (spoils) inside the bucket. The bottom of the bucket, which is hinged, is opened to allow the soils to dump into the spoil pile. The bottom of the bucket is closed, the bucket is reinserted into the hole, and the process is repeated as necessary to achieve the proper borehole depth.
For drilling with the bucket rig, groundwater must be at least 8-10ft below existing grade or the drill rig needs to be ramped up to achieve 8-10ft of head, which in some cases may require a surface casing. Water or biodegradable drilling fluids such as Revert, Guar Gum, or other synthetic polymers are added as needed to keep the borehole open during the drilling process. This is in lieu of large mixing/separation pits or tanks typical of other methods of drilling (i.e. reverse rotary).
The combination of the drilling fluid and the side cutting teeth producing an oversized borehole along with the fact that the drill cuttings are removed via the drill bucket, produces a well that is not smeared with the annulus of the borehole or drilling fluid, with suspended solids that could "cake" or produce lower yielding water wells. This makes the bucket drilling method a viable option in a variety of soil conditions. Over the years it has been a proven method for installing dewatering systems in the stratified soils found in the Houston region as well as other soil conditions found throughout the country.