Expandable Rock Bolt Anchor With Hardened Gripper
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Solution Overview
Problem
Existing rock bolts struggle to achieve a secure anchored connection in hard or very hard rock strata, particularly when the hole is filled with cement grout, which can act as a lubricant reducing frictional engagement between the anchor and the hole surface.
Innovation Solution
The development of an expandable anchor with at least one gripper that expands outwardly from an insertion condition to an anchor condition, featuring a body part made of hard material and a gripper portion made of an even harder material, such as cemented tungsten carbide, which penetrates or breaks into the facing wall of the hole to establish a secure grip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an expandable anchor is used to engage the facing surface of a drilled hole in hard rock strata, then the anchoring strength is improved, but the anchor cannot penetrate or grip the hard rock surface effectively
Solution Approach 1:
The anchor employs a differentiated structure where the body part is made of hard material and the gripper portion is made of an even harder material (such as cemented tungsten carbide). This local quality differentiation allows the gripper portion to penetrate or break into the hard rock facing surface while the body part provides structural support and expansion capability.
Solution Approach 2:
The anchor is constructed as a composite structure combining two different materials with different hardness properties. The body part uses hard material for overall strength, while the gripper portion uses exceptionally hard material (cemented tungsten carbide) specifically for penetrating and gripping the hard rock surface, creating a material composite that addresses both requirements.
2Stability of the object's composition
If cement grout is pumped into the hole before rock bolt insertion, then the hole is filled for support, but the grout acts as a lubricant reducing frictional engagement between the anchor and hole surface
Solution Approach 1:
The anchor is designed to be inserted into the grout-filled hole in the insertion condition with reduced diameter, allowing it to pass through the grout without significant frictional resistance. The grout provides preliminary support to the hole while the anchor penetrates through it to reach the facing surface for engagement.
Solution Approach 2:
The anchor engagement process is segmented into two distinct phases: first, the anchor travels through the grout in the insertion condition with minimal friction; second, the anchor expands to the anchor condition to engage the facing surface. This segmentation allows the grout to provide support without preventing anchor installation.
3Ease of operation
If the anchor diameter in the insertion condition is made slightly less than the hole diameter, then the anchor can travel into the hole without significant frictional resistance, but the anchor cannot grip the facing surface effectively
Solution Approach 1:
The anchor is designed with dynamic expandability, transitioning from the insertion condition with reduced diameter for easy insertion to the anchor condition with expanded diameter for effective gripping. This dynamic transformation allows the anchor to adapt its dimensions based on the operational phase, achieving both easy insertion and strong grip.
Solution Approach 2:
The anchor combines two functional states in a single device: the insertion condition for frictionless travel through grout and the anchor condition for gripping the facing surface. The expansion mechanism merges these two seemingly contradictory requirements into one adaptable structure that provides both ease of insertion and effective anchoring.
4Length of moving object
If rock bolts with length greater than 3m are used in underground mining, then the support range is extended, but the available room precludes the use of longer rock bolts
Solution Approach 1:
The rock bolt employs a flexible cable instead of a rigid rod or bar, allowing the cable to be unrolled from a cable reel to achieve any required length. This flexibility enables installation in confined underground mining spaces where longer bolts would otherwise not fit, while still providing extended support range when needed.
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 solution enables immediate and secure anchoring of rock bolts in hard rock strata, allowing for instant support of the rock strata before grout curing, and securing the cable within the hole, thereby facilitating safer and more efficient mining operations.
Implementation Method 1
the gripper portion having an outer facing gripping surface that projects beyond the body part in the direction of outward expansion of the gripper
Implementation Method 2
the anchor is expandable between a hole insertion condition and a hole anchor condition, the anchor having: at least one gripper that is expandable outwardly from the insertion condition of the anchor to the anchor condition of the anchor
Implementation Method 3
the gripper portion being formed of a material having a greater hardness than the body part
Data Source
Figure 1
Figure 2~4
Figure 5~6
AI summary
An anchor 12 for a rock bolt 10. The anchor 12 being connectable to a cable or rod 14 and being expandable between a hole insertion condition and a hole anchor condition. The anchor 12 has at least one gripper 32 that is expandable outwardly from the insertion condition of the anchor 12 to the anchor condition of the anchor 12 for gripping the facing surface of a hole in which the anchor 12 is installed. The gripper 32 comprises a body part 60 and a gripper portion 62, the body part 60 being formed from a hard material and the gripper portion 62 being formed of a material having a greater hardness than the body part 60. The gripper portion 62 has an outer facing gripping surface 66 that projects beyond the body part 60 in the direction of outward expansion of the gripper 32.