1. Pipe Blockage in CFG Pile Construction
Pipe blockage is a common issue in the long auger pipe pumping CFG pile construction process. It directly affects construction efficiency, increases labor intensity, and leads to material waste. If not resolved promptly, the mixed CFG pile material may lose moisture or harden, raising the risk of re-blockage and causing significant construction difficulties.
Causes and Solutions:
- Improper Mix Ratio & Poor Workability
- Ensure proper proportions of fine aggregate and fly ash.
- Recommended fly ash content: 60-80 kg/m³.
- Poor Mixing Quality
- The mixture must flow smoothly through rigid pipes, high-strength flexible pipes, bends, and variable-diameter pipes into the drill rod core.
- Optimal slump range: 16-20 cm.
- Equipment Defects
- Ensure smooth pipe connections, especially between bends and high-strength flexible pipes.
- Check gaskets for damage.
- Operator Error
- Proper training to prevent mishandling.
2. Cross-Hole (Pile Interference) in Saturated Fine Sand & Silt Layers
Cross-hole occurs when freshly poured pile material flows into adjacent boreholes. For example:
- After completing Pile #1 (30-40 min per pile), drilling Pile #2 may cause Pile #1‘s unset mixture to flow into Pile #2‘s hole, leading to sudden settlement (sometimes up to 2 meters).
- When pumping mixture into Pile #2, pressure may force material back into Pile #1, restoring its design elevation.
Preventive Measures:
- Increase Pile Spacing – Reduces shear disturbance from pile-driving equipment.
- Optimize Drill Bit Design – Improves drilling speed.
- Reduce Construction Rows – Switch from multiple rows to 1-2 rows to minimize disturbance.
- Skip Piling (Jump Driving) – Alternate pile sequences, but ensure timely removal of excavated soil to avoid delays.
3. Broken Pile: Causes and Repair Methods
After pile construction, cracks or fractures may appear due to:
- Rapid drill lifting (trapped air causes fractures).
- Insufficient mixing time (poor workability leads to honeycombing).
- External damage (e.g., excavation machinery impacting piles).
Solutions:
Shallow Broken Piles
- Remove the damaged section and reconstruct using the same mix to match design specifications.
Large-Scale Damage from Excavation
- Collaborate with design, supervision, and construction teams to assess.
- Conduct single-pile composite foundation load tests to compare intact vs. broken piles.
- If bearing capacity meets requirements, → No repair needed.
- If not, → Redesign required.
Preventive Measures
- Ensure high-quality shallow pile construction.
- Use manual excavation within 1 meter above the pile head elevation to avoid mechanical damage.
Pile Head Repair
- If the pile top is below design elevation, use higher-strength pea gravel concrete to restore height.
- Protect the surrounding soil during repair.
Key Takeaways for CFG Pile Construction
✔ Optimize mix design (fly ash, slump control).
✔ Ensure equipment integrity (pipe connections, gaskets).
✔ Prevent cross-hole (increase spacing, skip piling).
✔ Avoid broken piles (controlled drilling, manual excavation near pile heads).
By addressing these issues proactively, construction efficiency and pile quality can be significantly improved.
