Introduction
The pile fracture incident at a coastal city residential complex caused significant impacts on construction progress and substantial economic losses. This case study analyzes the causes, prevention measures, and treatment solutions for pile fractures, offering valuable insights for construction professionals.
1. Analysis of Pile Fracture Causes
Project Overview
The complex includes Buildings E# and F# (one basement level, 27 above-ground floors) with a total construction area of 33,759 m². During foundation excavation:
- Building E#: 37 out of 172 piles fractured (22% fracture rate)
- Building F#: 77 out of 141 piles fractured (55% fracture rate)
- Adjacent Buildings G# and H# also experienced minor pile fractures
Fractures showed consistent locations and concentrated distribution patterns.
Root Causes
1.1 Geological Conditions
- Former natural fishing pond site with 2.5m thick backfilled sand (water-retentive properties)
- Underlying thick layer (up to 7.6m) with high fluidity
- Fractures concentrated at /gravel layer interfaces
- Fluid caused squeezing and collapse during excavation
1.2 Insufficient Pile Driving Depth
- Design pile top elevation: -6.5m (-8.5m for elevator pits)
- Actual driving depth: 0-4m (mostly 0-3m) vs required 4.7m
- Particularly severe in Building F# (0-1.5m driving depth)
- Excavator movement in created lateral pressure on the piles
1.3 Improper Excavation Methods
- Overly steep slope excavation
- Temporary access road for tower crane installation caused secondary pile compression
- No site-specific excavation plan for challenging geological conditions
1.4 Weather Impacts
- Three typhoons during the excavation
- Heavy rainfall increased landslide risks
- Inadequate drainage measures
2. Prevention Measures for Prestressed Pipe Pile Fractures
2.1 Geological Considerations
- Conduct detailed, accurate geological surveys
- Implement soil replacement with quality sandy soil for backfill
2.2 Pile Construction Management
- Measure the original ground elevation for each pile location
- Calculate optimal pile length and driving depth (>4m for this project)
- Maintain consistent driving depths to create a uniform soil-pile system
- Proper pile driving sequence:
- From center outward (not inward)
- From the adjacent building side outward for dense pile areas
2.3 Proper Excavation Techniques
- Develop and validate excavation plans considering:
- Excavation sequence
- Slope gradient
- Support structures
- For E#/F# buildings: install concrete support piles first
- Equipment selection based on pile density (combine mechanical and manual excavation)
- Symmetrical excavation (no over-excavation or perimeter soil accumulation)
- For piles above design elevation:
- Manual excavation around piles
- Trim excess length before mechanical excavation
- Prevent machinery contact
Excavation Depth Guidelines:
- 软土基坑: ≤1m per layer
- Other conditions: ≤2m per layer
2.4 Water Management
- Implement well-point dewatering for groundwater
- Install cutoff walls (water-retaining piles)
- For rainfall, construct drainage ditches and sump pits
2.5 Monitoring and Emergency Response
- Monitor the adjacent building’s settlement and slope cracks
- Activate emergency plans when exceeding warning values
- Reinforcement measures:
- Steel sheet piles
- Timber piles
- Shotcrete slope protection
3. Pile Fracture Treatment
3.1 Steel Casing with Manual Digging Method
- Conduct low-strain integrity testing at fracture points
- For qualified piles: follow the national standard “Prestressed Concrete Pile” connection details
- For connections >1m: extend socket length to 500mm
- Pile core reinforcement:
- Install extended reinforcement cage (2m below fracture point)
- Main bars: Φ20 (HRB400)
- C35-C40 micro-expansion concrete
3.2 High-Pressure Jet Grouting for Soil Solidification
- Install triple-row jet grouting piles around fractures (leaving 2m working space)
- After achieving design strength:
- Lower ground level by 1.5m within the enclosed wall
- Install steel casing
- Manual excavation to 0.8m below the connection point
- Preserve original connection rebars
- Reconnect piles
Conclusion
This pile fracture incident serves as a costly lesson, highlighting the importance of meticulous construction management. Key takeaways:
- Contractors must:
- Establish experienced management teams
- Implement comprehensive risk controls
- Enforce strict quality and progress oversight
- Supervisors should:
- Provide project-oriented guidance
- Support construction teams effectively
By addressing these factors, projects can better achieve schedule, quality, cost, and safety objectives while creating added value.
