Expanding Rock Bolt Anchoring in Weak Strata
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Solution Overview
Problem
Existing rock bolts struggle to effectively anchor in weak or unstable rock strata, particularly in areas consolidated with low-strength cement paste, due to difficulties in achieving sufficient frictional engagement and resin bonding, leading to poor anchorage and increased risk of bolt egress.
Innovation Solution
A rock bolt design featuring an elongate tube with a displaceable wall section and an expander mechanism that displaces the wall section outwardly to embed into the surrounding strata, providing enhanced anchorage through gouging and embedding, rather than relying solely on frictional engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If friction-based rock bolts are used to anchor in weak strata, then installation is simpler, but anchorage strength is insufficient
Solution Approach 1:
The rock bolt incorporates a dynamic expander mechanism that transitions from a compact installed state to an expanded state, allowing the bolt to adapt to varying hole diameters and achieve sufficient frictional engagement even in weak strata where traditional fixed-diameter bolts would fail
Solution Approach 2:
The expander mechanism changes the dimensional parameters of the bolt during installation, increasing its external diameter from the installed size to an expanded size that provides adequate frictional engagement with the hole wall, thereby achieving sufficient anchorage strength
2Strength
If expanding rock bolts are used to increase frictional engagement, then anchorage strength improves, but hole drilling accuracy requirements increase
Solution Approach 1:
The expander mechanism provides dynamic adjustment capability, allowing the bolt to expand to the required diameter regardless of the initial hole size, thereby reducing the precision requirements for hole drilling while still achieving sufficient frictional engagement
Solution Approach 2:
The expander mechanism is pre-loaded in a compact state within the bolt body, ready to expand when installed in the hole. This preliminary preparation allows the bolt to achieve the necessary engagement diameter without requiring the hole to be pre-drilled to precise dimensions
3Productivity
If percussion insertion is used to drive rock bolt into hole, then installation speed increases, but hole wall damage increases
Solution Approach 1:
The expander mechanism is designed to expand gradually and controllably during or after insertion, distributing the expanding forces over time and space rather than applying them all at once during percussion driving, thereby reducing damage to the hole wall while maintaining installation efficiency
Solution Approach 2:
The bolt is pre-formed with the expander mechanism in a compact, low-stress state that can be easily inserted into the hole without causing damage. The expansion action is prepared to occur after insertion or during controlled expansion, avoiding the need to expand during the damaging percussion insertion process
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 design effectively anchors the rock bolt in weak strata by embedding the displaceable wall sections into the rock, enhancing resistance to longitudinal movement and improving overall stability and support, even in low-strength rock conditions.
Implementation Method 1
fixing the bolt within the hole by frictional engagement with the wall of the hole
Implementation Method 2
the expander mechanism being actuatable to displace the displaceable wall section to rotate about the hinge end to shift the anchor end outwardly from the tube
Data Source
AI summary
A rock bolt includes a tube having a leading end and a trailing end. An expander mechanism is disposed within the tube near the leading end. An elongate bar is disposed within the tube and is connected at a first end with the expander mechanism and at a second end with an anchor arrangement positioned at the trailing end of the tube. The elongate bar is arranged to actuate the expander mechanism and remain connected between the expander mechanism and the anchor arrangement while the expander mechanism is actuated. The tube has a displaceable wall section at the leading end, which has a hinge end proximal the leading end connecting the displaceable wall section to the tube. The expander mechanism can be actuated to displace the displaceable wall section to rotate about the hinge end to shift the anchor end outwardly from the tube.