Overview
Of the Gemini System
At the last rockbolt that mining engineers have been waiting for - a fully threaded mechanical anchor bolt that provides a solution to the risks associated with fully column grouting. This elegant rockbolt consists of a cold rolled fully threaded hollow section made up of twin halves fitted with an expansion shell on the one end. At the other end a free running nut, seat load indicator and bearing plate are attached. A short grouting tube with a conical gasket completes the assembly.
Advantages of the Gemini System
- Assured full column grouting
- Immediately active support
- Systemically the best support
- More robust bolt - no need for cumbersome breather tubes
- Easy & assured post-grouting makes it high-speed development friendly
- Deformed on the outside for better grout to steel bonding
- Lowest Total Cost of Ownership - can easily be adapted to a single pass system with lacing facility
Applications
- As a full column grouted mechanical anchor in all development ends
- Where dedicated crews can do grouting at a later stage, i.e. high speed development
- As a one pass system with lacing facility
- In-stope use
| SPECIFICATIONS |
| Lengths |
Available in standard lengths from 0,6m to 3,0m in increments of 0,3m. Non standard lengths are available on request. |
| Available Sizes |
All threads are formed by a cold-rolled process available in left-hand format. |
| Nominal Diameter |
Major Diameter |
Pitch |
14,5mm
20,0mm |
16,5mm
21,8mm |
5mm
6mm |
| Mechanical properties |
Nominal diameter |
Ultimate tensile strength Mpa (min.) |
Ultimate tensile load KN |
Elongation at fracture & (min.) |
14,5
20,0 |
600
600 |
100
180-200 |
6-8
6-8 |
Preparation
- Select an expansion shell with a diameter of not more than 5mm smaller than that of the hole.
- Slip off the plastic sleeve and ensure that at least 5mm of thread is protruding at the top end of the expander plug.
- When not using a spring-loaded expansion shell, expand the shell by threading it further onto the bolt, until the leaves fit snugly into the hole
Remove plastic
Assembly
- Ensure that the nut is free-running with at least 3 threads of the bolt protruding at the bottom end.
- The spherical side of the seat must face the bearing plate, while the flat side faces the bolt.
- The hollow side of the bearing plate should fit against the rock.
- The narrow end of the grout gasket must enter the hole first.
- Check that the filter tube protrudes from the narrow end by about 20mm. Ensure the filter pipe is threaded through the hole in the bearing plate.
Correct assembly
Installation
- Insert the assembly into a clean hole. Push the expansion unit to the back of the hole and force the conical gasket as far as possible into the mouth of the hole.
- Tension the bolt by using an impact wrench, rock drill or other suitable manual device. Correct tensioning has been achieved when the load-indicator has collapsed.
- The Gemini is now active and safe, allowing grouting to be undertaken immediately or at a later stage, if so required.
Load indicator collapsed
Grouting
- Pump a suitable grout through the short filter tube at a steady rate.
- As the grout rises up the drill hole, trapped air is displaced through the hollow section of the bolt.
- Reduce pressure once the grout starts to squirt from the hollow section
- Remove the pump and immediately seal off the filter tube.
Tie off grouting tube
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