Extendable Drill Bit Assembly for Reliable Underreaming
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Solution Overview
Problem
Conventional down-the-hole under reaming systems face limitations such as high operational costs and reliability issues due to the need for constant contact with the borehole to maintain the extended configuration, leading to undersized holes in challenging ground conditions like sand or voids.
Innovation Solution
A percussive down-the-hole drill hammer assembly with an extendable drill bit system, where drilling lug segments are moved from an initial retracted configuration to an extended configuration upon full engagement with a pilot drill bit, allowing for efficient enlargement of the cutting face diameter without constant borehole contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If lug based systems use radially extendable lugs that require constant contact with the borehole to remain extended, then the cutting face diameter can be enlarged, but the system becomes unreliable in challenging ground conditions like sand or voids where back pressure is insufficient
Solution Approach 1:
The drilling lugs are designed to dynamically extend and retract based on operational conditions. During the hammering phase, lugs extend radially outward to enlarge the hole diameter. During the extraction phase, lugs retract radially inward to allow passage through the casing. This dynamic transformation allows the system to adapt its geometry to different operational requirements without compromising reliability in challenging ground conditions.
Solution Approach 2:
The drilling system is divided into modular components: a pilot bit that drills the initial hole, extendable drilling lugs that can be deployed independently around the pilot bit, and a casing for extraction. The drilling lugs are segmented and can be extended or retracted independently, allowing the system to maintain reliability in varying ground conditions while achieving the required hole enlargement.
2Area of moving object
If hinged wing systems rotate the wing outward by clockwise torque requiring contact with the borehole, then the kerf for casing clearance can be created, but the system fails when borehole contact is lost, leaving an undersized hole
Solution Approach 1:
The hinged wings are designed to dynamically change their position from a retracted state (during pilot hole drilling) to an extended state (during kerf cutting). The wings can be forced outward by clockwise torque when borehole contact is available, but can also be held in position by the hinge mechanism itself, providing reliability even when continuous borehole contact is lost. This dynamic adaptability resolves the contradiction between creating sufficient kerf width and maintaining reliability.
3Reliability
If concentric systems use a lost crown or ring bit to create a kerf, then the casing can be sealed from contamination, but the system becomes costly due to the ring bit being discarded and the high number of piles required
Solution Approach 1:
The pilot bit and drilling lugs are designed to be temporary, discardable components that perform their function (drilling the pilot hole and creating the kerf) and then are removed or discarded. The permanent, valuable casing remains in place to provide long-term sealing and structural support. This approach recovers the permanent infrastructure (casing) while allowing temporary components to be discarded, reducing long-term operational costs compared to systems where expensive components must be repeatedly installed and removed.
Solution Approach 2:
The drilling system separates the temporary drilling functions (pilot bit, drilling lugs) from the permanent infrastructure (casing). This segmentation allows the temporary components to be optimized for drilling performance and discarded after use, while the permanent casing is optimized for long-term sealing and structural requirements, reducing overall operational costs.
Data Source
AI summary
A down-the-hole drill hammer assembly includes a casing, a drill stem, a drilling lug segment and a pilot drill bit is provided. The drill stem is housed within the casing and includes an abutment surface. The drilling lug segment is slidably engaged with a distal end of the drill stem and movable between an initial configuration and an extended configuration. The drilling lug segment includes a proximal end engageable with the abutment surface of the drilling lug segment. The drill stem is movable between first and second positions within the pilot drill bit. In moving to the second position, the drill stem slidingly engages the drilling lug segment and moves the drilling lug segment to the extended configuration.