Rock Bolt Wedge Expansion for Low-Friction Installation
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Solution Overview
Problem
Existing rock bolts face challenges such as high friction during installation, buckling of the outer body, and inability to pre-tension the formation, especially with longer bolts and weaker installation equipment.
Innovation Solution
A rock bolt design featuring a central rod with a threaded leading portion and a tubular outer body, including first and second wedge means that allow the outer body to be pulled into the formation via the central rod, reducing friction and enabling pre-tensioning by expanding the outer body radially.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the bolt is driven into the formation by repeatedly impacting the outer body, then the bolt is forced into the formation, but the outer body may buckle and/or the trailing end of the bolt be damaged, especially for bolts longer than three meters
Solution Approach 1:
The patent inverts the conventional driving approach by applying impact force to the leading end of the outer body rather than the trailing end. The driving device impacts the leading end, which transmits force through the central rod to the expansion mechanism, causing the outer body to expand and engage the formation from the leading end. This inversion prevents buckling and trailing end damage while enabling installation of longer bolts.
2Adaptability or versatility
If handheld air legs are used to hammer in the bolts, then installation can be performed with portable equipment, but the equipment does not have enough power to hammer in the bolts efficiently
Solution Approach 1:
The patent extracts the expansion function from the driving process. By separating the expansion mechanism (wedges and outer body expansion) from the driving action, the system allows the central rod to be driven into the formation first using portable equipment, then expanded separately. This extraction enables the use of weaker handheld air legs for driving while maintaining effective bolt installation and expansion.
3Strength
If the outer body/split tube is present in mechanically anchored rock bolts with anchoring wedges, then the bolt can be expanded and anchored, but the outer body prevents the rock plate from moving closer to the leading end portion of the rock bolt, preventing pre-tensioning
Solution Approach 1:
The patent segments the bolt structure into distinct functional zones: the outer body with wedges for anchoring, and the central rod for tensioning. The outer body is designed to expand and anchor at specific locations, while the central rod can be independently tensioned. This segmentation allows the rock plate to move closer to the leading end portion as the central rod is tensioned, enabling pre-tensioning of the formation while maintaining anchoring capability.
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
This design reduces the force required for installation, prevents buckling, allows use of weaker equipment, and enables effective pre-tensioning of the formation, enhancing the installation process.
Implementation Method 1
a first wedge means (8) attached to the leading portion (3) of the central rod (2), and a second wedge means (9) attached to the leading portion (6) of the outer body (5) between the first wedge means (8) and the trailing portion (7) of the outer body (5). Also, the first wedge means (8) and the second wedge means (9) are configured such that the first wedge means (8) is able to force the second wedge means (9) radially outwards about the longitudinal axis (10) of the rock bolt (1) upon movement of the first wedge means (8) in a direction towards the trailing portion (4) of the central rod (2) to thereby radially expand the outer body (5).
Implementation Method 2
The leading portion of the outer body (5) is provided with one or more ledge means (11). Also, the central rod (2) is provided with a drive means (12) configured to drive the ledge means (11) upon movement of the drive means (12) in a driving direction (13) of the rock bolt (1) to thereby force the outer body (5) in the driving direction (13) via the ledge means (11).
Data Source
AI summary
A rock bolt includes a central rod, a tubular outer body provided around the central rod, and an expansion mechanism arranged for radially expanding the leading portion of the outer body. The rock bolt is arranged such that the outer body at installation is pulled into a bore of a formation from the leading portion of the outer body using a driving force applied via the central rod.