Microtunneling Drill String Latch and Reamer Torque Control
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Solution Overview
Problem
Existing microtunneling methods face challenges in accurately directing drill heads, leading to unnecessary spoil removal and inefficiencies due to the mismatch between the pilot hole diameter and the reamer's cutting head diameter, and the inefficient removal of spoil through vacuum arrangements.
Innovation Solution
A drill string with adjustable latch connections and a reamer assembly that includes a gearbox to increase torque, a cylindrical housing to protect the gearbox, and a spoil removal system that directs spoil through the borehole rather than the drill string, along with cooling mechanisms to enhance efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a drill head is used to drill a hole through the ground, then a micro tunnel can be produced, but it is difficult to accurately direct the drill head leading to deviations from the preferred line and unnecessary spoil removal
Solution Approach 1:
The drilling process is divided into two distinct stages: first drilling a small diameter pilot hole with a drill head, then enlarging it with a reamer assembly. This segmentation allows the pilot hole to serve as an accurate guide path, preventing deviations and unnecessary spoil removal while the reamer efficiently enlarges the hole along the established trajectory.
Solution Approach 2:
A pilot hole is drilled first as a preliminary action to establish the desired path and trajectory before the reamer assembly enlarges the hole. This preliminary drilling action creates a guide path that ensures subsequent reaming occurs precisely along the preferred line, eliminating the need for continuous directional control during the enlarging process.
2Volume of moving object
If a reamer assembly is used to enlarge the pilot hole, then the tunnel diameter can be increased, but the drill string torque is insufficient to rotate the reamer cutting head effectively at the larger diameter
Solution Approach 1:
A gearbox is introduced as an intermediary mechanism between the drill string and the reamer cutting head. The gearbox receives rotational input from the drill string and transmits it to the reamer cutting head with increased torque, enabling the reamer to effectively cut at the larger diameter despite the limited torque available from the drill string alone.
Solution Approach 2:
The direct mechanical connection between the drill string and reamer is replaced with a gear-based mechanical system. The gearbox provides mechanical advantage through gear ratios, substituting a simple direct-drive system with a more complex but torque-multiplying gear mechanism that enables effective reaming at larger diameters.
3Productivity
If spoil is removed through the pilot hole using a vacuum arrangement, then spoil can be extracted, but the cutting head churns spoil rather than cutting into the working face due to diameter mismatch
Solution Approach 1:
The spoil removal function is extracted from the drill string and pilot hole system and assigned to a separate dedicated spoil removal conduit. This allows the reamer cutting head to focus entirely on cutting into the working face at the correct diameter, while the separately positioned spoil removal conduit efficiently extracts spoil without interfering with the cutting process.
Solution Approach 2:
A separate spoil removal conduit acts as an intermediary system for spoil extraction, positioned separately from the drill string and pilot hole. This intermediary conduit provides a dedicated path for spoil removal that does not conflict with the reamer's cutting operation, eliminating the churnage problem caused by the diameter mismatch between the pilot hole and reamer cutting head.
4Ease of operation
If the drill string is under tension to draw the reamer assembly back through the pilot hole, then the reamer can be pulled through, but the latch connection between string segments experiences pressure that may jam normal operation
Solution Approach 1:
The latch connection is designed with adjustable tolerance that can accommodate the dynamic pressures experienced during reamer retrieval. The latch mechanism can adapt its clearance and engagement characteristics in response to the tensile loads and pressure conditions, preventing jamming while maintaining secure connection during both drilling and retrieval operations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution reduces spoil removal inefficiencies by allowing precise alignment and increased torque, improving the drilling process efficiency and spoil extraction, while maintaining gearbox durability and reducing energy consumption.
Implementation Method 1
The torque supplied by the drill rod to the reamer cutting head will be the same as that supplied to the drill head
Implementation Method 2
The spoil will generally be removed also through the pilot hole, often using a vacuum arrangement
Data Source
AI summary
This invention relates to a drill string (32) for use with micro tunnelling apparatus (1) having a cutter (21) at a distal end of the drill string (32) and external drive mechanism (2) at a proximal end of the drill string (32). The drill string (32) being formed by a plurality of connected string segments (13), each string segment (13) with a drive shaft (33) aligned along the central axis for rotation there about and an elongate casing (34) that houses the drive shaft (33). The front end of one string segment (13) is adapted to connect with the back end of another string segment (13) to form the drill string (32) by way of a latch connection, the latch connection being adjustable so as to vary the tolerance between said front end of one string segment (13) and said back end of another string segment (13) while connected.