Concentric Drill Assembly for Granular Column Formation
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Solution Overview
Problem
Existing methods for forming granular columns in the ground, such as stone columns, face challenges like contamination, equipment cost, and inefficiency in soft and non-cohesive soils, particularly with high groundwater levels and collapsing ground conditions, which limit their applicability and quality control.
Innovation Solution
A drill assembly comprising a first tube drill and a second drill with a drill flight, configured concentrically, that forms granular columns primarily through vertical compaction without vibratory compaction, allowing for controlled aggregate feeding and withdrawal to create a granular column with desired characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hole is drilled first and then filled with stone aggregate using a cone shaped vibrator, then the granular column can be formed, but the method is not suitable for collapsing ground as the walls of the hole collapse which may prevent the column from being formed or contaminate the column
Solution Approach 1:
The patent employs a nested drill configuration where a second drill with drill flight is positioned inside a first drill tube. This nested structure allows the inner drill to advance through the ground while the outer tube contains the displaced material, preventing hole wall collapse and contamination of the granular column being formed.
2Object-affected harmful factors
If compressed air is used to reduce fines blowout, then the contamination problem can be reduced, but the equipment cost increases significantly
Solution Approach 1:
The patent extracts and removes fines and contaminated material through the drill flight structure during the drilling process itself, eliminating the need for additional compressed air systems or other expensive contamination control equipment that would be required by conventional methods.
3Productivity
If an impellor is used to distribute crushed stone radially, then the granular column can be formed faster with more predictable properties, but the method is not suitable for ground with high levels of non-cohesive materials such as sand
Solution Approach 1:
The patent employs a dynamic drill flight structure that can adapt its configuration based on ground conditions. The drill flight geometry and operational parameters can be adjusted to handle different soil types including non-cohesive materials like sand, while maintaining efficient aggregate distribution and column formation speed.
4Manufacturing precision
If the second drill includes a drill flight configured to feed aggregate, then the granular column can be formed with controlled aggregate placement, but the drill assembly becomes more complex
Solution Approach 1:
The patent combines multiple functions into the drill assembly: the first drill tube serves as both a drilling tool and a containment structure, while the second drill with its drill flight simultaneously advances the borehole and feeds aggregate material. This merging of functions achieves precise aggregate placement control without requiring separate, additional equipment systems.
Data Source
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AI summary
A drill assembly for forming in ground granular columns without the need for vibratory compaction, said drill assembly includes a first drill (10) and a second drill (11), where the first drill is a tube (7), and the second drill includes a drill flight (26), wherein said first and second drills are concentric, and the second drill (11) is configured to lie at least partially within the first drill (10); such that the drill assembly is configured to form the granular column with primarily vertical compaction; when the drill assembly arrives at the required depth, the second drill (11) is used to feed an aggregate to a lower terminal end of the drill assembly, thus forming the granular column as the drill assembly is withdrawn.