Common Treatment Methods for Broken Piles
1. In-Situ Pile Reconstruction
For broken piles detected during construction or via ultrasonic testing, the most thorough solution is complete removal and reconstruction of a new pile in the same location. This method offers excellent results but is complex, time-consuming, and costly. It is typically used based on project importance, geological conditions, and defect severity.
2. Pile Splicing
To ensure quality, concrete pouring is halted, and the conduit is withdrawn. The splicing process involves:
- Ultrasonic testing to identify the sound concrete section.
- Well-point dewatering, excavation, and a #20 plain concrete retaining wall reinforced with steel hoops.
- Manual chiseling to expose the intact section, followed by cast-in-place concrete pouring using drilled shaft methods.
3. Core Drilling Method
This challenging technique involves:
- Drilling an 80cm diameter shaft beyond the defective section while dewatering.
- Cleaning the shaft, placing a rebar cage, and pouring expansive concrete using drilled shaft methods.
Progress is slow, and water infiltration issues can lead to delays and increased costs.
4. Re-Driving and Supplementation
For driven piles with disconnected joints:
- Re-driving suspect piles to restore vertical load capacity.
- Adding full-length piles to compensate for insufficient bearing capacity and improve seismic resistance.
5. Rectification Method
For short, inclined but unbroken piles (e.g., due to excavation), hydraulic jacking can correct alignment.
6. Pile Cap Enlargement
Expanding the pile cap is necessary when:
- Pile misalignment exceeds design tolerances.
- Soil-pile interaction is required to share structural loads.
- Uneven settlement or seismic resistance improvements are needed by connecting isolated caps.
Preventive Measures for Broken Piles
1. Ensure Pile Tensile Strength
- Design verification: Account for frost heave forces in cold regions.
- Concrete quality: Minimum 350kg/m³ cement, with actual strength 10-15% higher than design.
- Reinforcement standards: Use tested steel and proper welding techniques.
2. Optimize Construction Planning
- Conduit preparation: Use 2m mid-sections and 4-6m base sections for smooth assembly. Limit disassembly time to <15 minutes.
- Concrete workability: Maintain 18-22cm slump, 0.5-3.0cm aggregate size (max 4.0cm), and >5h initial setting time (use retarders if needed).
- Conduit embedment depth: Keep between 1-6m to avoid mud intrusion or conduit fracture.
3. Prevent Water Infiltration
- Conduct pressure and tensile tests on conduits before use.
- Calculate the initial concrete volume to ensure proper embedment and continuous pouring.
4. Avoid Borehole Collapse
- Monitor water levels and retaining wall integrity.
- Maintain hydrostatic pressure and minimize vibrations near the borehole.
5. Over-Pouring and Splicing
- Pour 0.5-1m above design grade, then trim post-curing (retain 30cm for splicing).
- Clean exposed surfaces with water before splicing.
Conclusion
Broken piles in bridge drilled shafts can lead to severe consequences. Contractors must:
- Implement strict quality control and contingency plans.
- Follow scientific procedures and real-time monitoring.
- Engage expert reviews for accurate diagnosis and cost-effective solutions.
By enforcing material standards, welding protocols, and operational precision, pile fractures can be effectively prevented.
