Drilling Assembly Single-Pass Rock Bolt Installation
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Solution Overview
Problem
Conventional rock bolt installation in rock bodies is time-consuming and inefficient, particularly for friction bolts, as they require a two-step process involving drilling and subsequent insertion, often resulting in the loss of drill bits and reduced bolt strength due to incompetent rock engagement.
Innovation Solution
A drilling assembly with a detachable drill bit and rock bolt sleeve featuring a thread engagement system allows for simultaneous drilling and rock bolt insertion in a single pass, where the drill bit is detachably joined to the drill string with a spigot and socket connection, and the sleeve is frictionally engaged and wedged into the rock body using a thread engagement formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a two-step process is used for rock bolt installation (drilling then insertion), then the rock bolt can be properly installed, but the installation time is excessive and productivity is low
Solution Approach 1:
The patent combines the drilling operation and rock bolt insertion into a single integrated process. The drill string with detachable drill bit drills the borehole while the rock bolt sleeve is simultaneously inserted through the drill string into the borehole. After drilling completes, the drill bit is detached and the rock bolt is fully installed in one continuous operation, eliminating the time loss between separate drilling and insertion steps.
2Ease of repair
If a detachable drill bit is used in one-step friction bolt installation, then the drill string can be retrieved, but the drill bit is lost in the borehole
Solution Approach 1:
The rock bolt sleeve is designed to nest over the drill string during the drilling operation. The sleeve has an internal diameter that accommodates the drill string, allowing it to be inserted through the drill string into the borehole. After drilling completes, the drill bit is detached from the drill string while the sleeve remains positioned in the borehole, effectively nesting the drill string within the sleeve during the process.
3Adaptability or versatility
If friction bolts are used in incompetent rock, then installation is possible, but the effective bolt strength is reduced due to insufficient frictional retention
Solution Approach 1:
The rock bolt system is segmented into two distinct anchoring mechanisms: a frictional anchor along the length of the sleeve and a mechanical point anchor at the downhole end. The sleeve's external surface provides frictional engagement with the borehole wall, while the downhole end features a mechanical anchor device that expands or engages with the rock body. This segmentation allows the bolt to function effectively in incompetent rock by combining distributed frictional support with concentrated mechanical anchoring at the critical downhole location.
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
Enables efficient and effective single-pass installation of rock bolts with improved bolt strength by ensuring the drill bit remains in place, even through incompetent rock, reducing installation time and maintaining bolt integrity.
Implementation Method 1
a drill bit arranged to be detachably joined to the downhole end of the drill string
Implementation Method 2
the rock bolt functions as a friction bolt having a point anchor at its downhole end
Implementation Method 3
the sleeve having a thread engaging formation at or near its downhole end arranged to cooperate with the external screw thread of the drill bit
Implementation Method 4
whereby the tapered external screw thread of the drill bit is engaged within the tapered internal screw thread of the sleeve to wedge the rock bolt and the drill bit against the rock body
Data Source
AI summary
A drilling assembly is disclosed for drilling a borehole in a rock body and inserting a rock bolt within the borehole in a single pass. The drilling assembly includes an elongated drill string having a downhole end. A drill bit is detachably joined to the downhole end of the drill string, with the drill bit having an external screw thread extending in an axial direction of the drill string. The drill string is surrounded by a rock bolt sleeve that has a thread engaging formation at or near its downhole end and that is arranged to cooperate with the external screw thread of the drill bit so that the drill bit is able to be screwed into the rock bolt sleeve.