Rock Bolt Expander Mechanism for Dynamic Anchorage
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Solution Overview
Problem
Existing rock bolts do not effectively increase anchorage capacity during rock displacement, as the expander mechanism fails to expand under loading, leading to reduced grip in weaker rock formations, where the bolt may crush and be easily pulled out.
Innovation Solution
A rock bolt design featuring an elongate tube with an expander mechanism that includes first and second expander elements, where the second expander element shifts radially outward during actuation, providing additional grip by engaging the rock surface, enhancing anchorage capacity, especially in weaker rock bodies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the expander mechanism is activated once the rock bolt is inserted, then the rock bolt provides anchorage within the rock body, but the expanded mechanism will not increase expansion under loading during rock displacement
Solution Approach 1:
The expander mechanism transitions from a static expanded state to a dynamic state that can further expand under loading. The second expander element is designed to shift radially outward when axial load is applied during rock displacement, allowing the anchorage capacity to adapt and increase in response to operational conditions.
Solution Approach 2:
The physical state of the expander mechanism changes from a fixed expanded configuration to a configuration that can alter its expansion parameters under load. The second expander element's radial position changes from an initial expanded state to a further expanded state when subjected to axial forces during rock displacement, modifying the anchorage characteristics.
2Ease of manufacture
If the rock bolt is anchored in weaker rock, then installation is feasible, but the expanded tube may crush the rock at the engagement interface making the rock bolt more easily pulled out
Solution Approach 1:
The expander mechanism is divided into two separate expander elements that perform different functions. The first expander element provides initial expansion and frictional engagement suitable for weaker rock, while the second expander element provides additional radial engagement that prevents pull-out under loading conditions.
Solution Approach 2:
Different parts of the expander mechanism have different engagement characteristics with the rock. The first expander element creates a friction-based engagement suitable for softer rock formations, while the second expander element creates a mechanical interlock that resists pull-out forces, with each element optimized for its specific function.
3Device complexity
If a single expander element is used, then the device complexity is reduced, but the anchorage capacity and dynamic performance are insufficient
Solution Approach 1:
Two expander elements are merged into a single integrated expander mechanism that operates sequentially. The first expander element expands initially to provide frictional engagement, then under axial loading, the second expander element shifts radially to provide additional anchorage, combining both functions in one mechanism.
Solution Approach 2:
The second expander element is positioned within the tube structure and can shift radially outward from a retracted position to an engaged position. The nested configuration allows the second expander element to be stored within the tube during insertion, then deployed when needed without significantly increasing the overall diameter of the rock bolt.
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 rock bolt achieves increased anchorage capacity and retention in rock bodies by maintaining frictional engagement with the tube and additional engagement of the second expander element, consistently achieving industry-desirable pull-out loads and improved dynamic capacity.
Implementation Method 1
maintaining frictional engagement with the tube and additional engagement of the second expander element
Data Source
Figure 1~3
Figure 4~7
AI summary
A rock bolt 10 comprising: an elongate, generally circular tube 12, the tube 12 having a leading end 14 and a trailing end 16, an expander mechanism 17 disposed within the tube 12 in the region of the leading end 14, an elongate tendon 22 disposed longitudinally within the tube 12 and in connection at or towards a first end of the tendon 22 with the expander mechanism 17 and in connection at or towards a second and opposite end of the tendon 22 with an anchor arrangement 43 positioned at the trailing end 16 of the tube 12, the tendon 22 being actuatable to actuate the expander mechanism 17 and to remain connected between the expander mechanism 17 and the anchor arrangement 43 while the expander mechanism 17 is actuated, wherein the tube 12 has an opening 26 in the region of the leading end 14 and the expander mechanism 17 includes first and second cooperating expander elements 18, 20, in which the first expander element 18 is attached to an end of the tendon 22 for movement axially within the tube 12 towards the anchor arrangement 43 upon actuation of the expander mechanism 17 and the second expander element 20 is restrained relative to the tube opening 26, the second expander element 20 being shifted radially through the tube opening 26 as the first expander element 18 is shifted axially within the tube 12 towards the anchor arrangement 43.