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Gemini Bar®
Gemini Bar® is the elegant solution for full column grouted mechanical anchor bolts. It is a cold rolled, fully threaded bar made up of twin halves, resulting in a breather hole down its middle. An expansion shell is fitted to one end and at the other end a free running nut, seat, load indicator and bearing plate are attached. A short grouting tube with a gasket completes the assembly.
ADVANTAGES
- 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
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 (mm) | Major diameter (mm) | Pitch (mm) | ||
|---|---|---|---|---|
| 14,5 20,0 | 16,5 21,8 | 5 6 | ||
| Mechanical properties | Nominal diameter (mm) | Ultimate Tensilve Srength Mpa (min) | Ultimate Tensile Load KN | Elongation at Fracture % (min) |
| 14,5 20,0 | 600 600 | 100 180-200 | 6-8 6-8 | |
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
- In-stope use
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 pushing it further onto the bolt, until the leaves fit snugly into the hole.
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 filler tube protrudes from the narrow end by about 20mm. Ensure the filler tube is threaded through the hole in the bearing plate.
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 bar is now active and safe, allowing grouting to be undertaken immediately or at a later stage, if so required.
GROUTING
- Pump a suitable grout through the short filler 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 filler tube.
