- Areas of Expertise
- Construction Methods
- Machinery & Equipment
PASSIVE ANCHORAGE AND SHOTCRETE APPLICATION METHODS
1.0-) SCOPE OF WORK
Used in deep excavations to cover the drilling surface with nut bolt and shotcrete. The reason for the preference of this method is the the resistance it provides against vertical displacements within the structure.
2.0-) MACHINERY AND EQUIPMENT
- Drilling Rig designed for rotary plus percussive operation
- Rods + Down The Hole Hammer + Consistent Bit
- Continous Flight Auger + Consistent Bit
- Casings and bentonite mixing and pumping set
- Maxbit / Odex
- Air compressor
- Cement Injection Unit (pump + mixer + agitator)
- Pre-stressing Unit
- Water Pump
- Generator (If needed)
3.0-) DETAILS OF METHODS OF CONSTRUCTION
Following the applications specified in the project,
In nut bolt drilling applications rotary and/or percussive drilling is used. In rough surfaces, the drilling is achieved by using Down the Hole system. In plastic clayey soil conditions or on fills, Augers with clay bits are used. As in temporary pre-stressed anchor constructions, in filled surfaces or strata exposed to flowing groundwater, to prevent collapse, temporary casings are used. It is important to drive away the excavated earth and debris in this process because it affects drilling rate and quality.
The adhesion force between grout and tendon depends on mixture ratio of ingredient of the injection, type of preparation and method of injection. For hard and rocky soils, prestress strand is placed to the hole by manpower.Using the first HDPE pipe, the grout is injected into the hole and after two hours procedure is repeated by using the second pipe, which is a procedure fulfilled for safety. For clayey or fill soils, pre-grouting is accomplished by placing a pilot pipe before placing anchor strands. Fresh portland cement is used. The water in the mix should have the same quality as the concrete. The definitive property of the cement slurry is w/c ratio, the optimum being in between 0.42 and 0.45. Expander, retarder, accelerator, fluidifier etc.should at this stage be added to the mixture. Briefly, the prepared mixture at desired ratios are injected to the hole at high pressure. During injection, it is most important that the present water within the hole migrates.
3.3-) PRODUCTION OF SHOTCRETE
After the injection and soil nail drilling processes of the inclined(with the design tilt) pile, surface cleaning is done. Following this, with the data provided by the project, the mesh reinforcements setting stage is completed with complying to predefined concrete depth values.
The shotcrete with required fineness is obtained by mixing the concrete purchased from the ready-mixed concrete plant with the proper amount of sigunit dust(4% of cement weight per m3) in the shotcrete machine. The pressurized air from the compressor head meets the recently hydrated mix at the nozzle socket whereafter it is directed to the mirror surface(?). Initially, the injection should be 10 cm thick, just enough to cover the reinforcing elements. After the completion of welding of nut bolt plates more shotcrete is sprayed over the surface to reach the thickness specified in the project. For successful completion of this process, it is essential to fix the amount of sigunit dust, amount of hydration at the exit nozzle and operators distance to the mirror surface.
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