Ground Anchor Construction Method
This method defines the selection of machinery, equipment, materials, preparation, installation, and prestressing procedures necessary for the construction of temporary and permanent prestressed ground anchors with capacities between 10–100 tons.
All works shall comply with DIN 4125 Ground Anchorages.
1. Site Preparation
The work area must be kept level, compact, and dry for efficient machine operation. Heavy equipment (drilling rigs, cranes, mixers, pumps) must be able to operate without sinking more than 10 cm. Proper drainage must be maintained, and groundwater or drilling slurry must be removed continuously.
2. Soil Information
Execution methods follow the geotechnical reports.
3. Environmental Information
Underground and surface obstacles (steel, concrete, utilities) must be identified officially and removed by the employer.
4. Anchor Layout & Tolerances
Anchor locations are set out by site management. Verticality and inclination tolerances must comply with the project. Adjacent drilling must not be performed within 1.5 m for at least 24 hours.
5. Components of Prestressed Anchors
• Anchor Head: Transfers prestress force to the retaining system.
• Free Tendon Length: Carries the prestress force elastically.
• Bond (Root) Length: Transfers the force to stable soil through cement-grout adhesion.
6. Anchor Production
• Excavation is carried out in stages according to soil conditions.
• Drill holes to the specified diameter, inclination, and length.
• Place tendon bundle without contamination.
• Pressure grout the bond zone to ensure adhesion strength.
• Construct waling beam (steel or RC).
• Apply prestressing.
7. Drilling Methods
Depending on soil/rock conditions:
– Auger drilling
– Rock bit
– Top hammer
– Down-the-hole hammer
– ODEX
– Casing systems
Root zone enlargement may be performed in clayey soils to improve bond strength.
8. Tendon Fabrication & Installation
• High-strength low-relaxation 7-wire strands (0.5", 0.6" or 0.7") are used.
• Free length is sheathed in HDPE to prevent bonding.
• Bond length uses spacers and centralizers.
• Permanent anchors receive corrosion protection (grease-filled plastic sheaths, spiral tubes).
• Tendons are placed with proper alignment and tied to prevent twisting.
9. Grouting
• Water/cement ratio ≈ 0.45
• Grout is mixed 3–5 minutes and injected at 1–3 bar until clean grout comes out of the hole.
• If leakage occurs, secondary “re-grouting” is performed after 2–4 hours.
• Accelerators may be used in early stressing situations.
10. Prestressing
• Prestressing may begin 6 days after grouting (earlier if additives used).
• Anchors must be stressed in a skipped sequence.
Testing Loads:
– Temporary anchors: up to 1.15 × Working Load
– Permanent anchors: up to 1.25 × Working Load
Hold times and displacement readings follow DIN 4125.
11. Reinforced Concrete Works
Excavation is controlled by survey team. Waling beams and anchor plates are installed with proper formwork, compaction, and vibration.
12. Materials
• Cement: min. 28-day strength ≥ 325 kg/cm²
• Water: Clean and sediment-free
13. Machinery
• Drilling rig suitable for project depth
• Grout injection set (mixer + tank + pump)
14. Measurements & Reporting
Reports include:
Anchor location, number, type, drilling method, inclination, length, grout ratio, soil layers, prestress records, load-displacement readings, and lock-off load.
15. Quality Control
All works follow project QC procedures (YY.09) and material acceptance criteria (T06).