Introduction to Sediment Challenges in Rotary Drilling Piles
Rotary drilling rigs offer high automation levels and strong adaptability, yet significant quality issues persist in pile construction due to varying equipment performance, operator skill levels, and site management capabilities, particularly when dealing with complex ground conditions. The absence of standardized construction specifications and systematic construction methods has led to widespread quality defects, with excessive bottom sediment accumulation emerging as one of the most common problems.
Excessive sediment thickness severely impacts pile foundation quality by:
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Restricting end-bearing capacity development
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Increasing settlement displacement
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Creating potential safety hazards for superstructures
Current pile foundation specifications establish clear requirements for sediment thickness:
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End-bearing piles: ≤50mm (JGJ94-2008)
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Friction piles: ≤100mm (JGJ94-2008)
Despite these standards, inadequate operator training, lax quality control, and complex geological conditions continue to cause sediment overage problems. This article analyzes sediment causes in Shenzhen rotary drilling projects and presents effective secondary hole cleaning methods with optimization strategies.
Causes and Control Measures for Pile Bottom Sediment
1. Hole Wall Collapse
Causes:
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Unstable surface soil layers
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Low slurry specific gravity with poor suspension capacity
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Rapid drill tool extraction creates suction
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Insufficient slurry level maintenance
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Wall contact during tool or rebar cage installation
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Prolonged post-drilling waiting time
Control Measures:
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Install an appropriately sized steel casing
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Increase slurry viscosity and specific gravity
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Control drilling parameters and extraction speed
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Maintain proper slurry levels
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Ensure vertical tool and cage installation
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Minimize construction intervals
2. Slurry Sedimentation
Causes:
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Substandard slurry parameters
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Excessive waiting time before concreting
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High sand content in the slurry
Control Measures:
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Optimize slurry formulation and monitoring
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Reduce construction intervals
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Implement slurry sedimentation tanks or separators
3. Drilling Residue
Causes:
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Worn or deformed drill tools
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Inefficient drill bit design
Control Measures:
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Select proper drilling tools
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Maintain tool components
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Optimize tooth arrangement
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Increase cleaning frequency
4. Cleaning Process Issues
Causes:
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Excessive suction is causing the wall to collapse
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Substandard slurry performance
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Inappropriate cleaning method selection
Control Measures:
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Control the pumping force
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Adjust slurry parameters
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Select the optimal secondary cleaning method
Secondary Hole Cleaning Technologies
1. Slurry Direct Circulation Cleaning
Process Principle:
Pumped slurry flows through the tremie pipe to the hole bottom, carrying sediment upward through the annulus. The slurry then returns to the sedimentation system for recycling.
Key Considerations:
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Select proper pump capacity (12-30KW 3PN pumps)
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Minimize pipeline resistance
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Regularly clean sedimentation systems
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Adjust the pipe position during operation
2. Cyclone-Assisted Direct Circulation
Process Principle:
This enhanced method incorporates slurry cyclones to pre-separate coarse particles before the slurry enters the hole, significantly improving efficiency. Our patented technology has been recognized as a municipal and provincial construction method.
Key Considerations:
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Monitor cyclone operation
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Adjust the discharge valve properly
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Maintain a dedicated slag discharge area
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Match the cyclone with the pump capacity
3. Pump Reverse Circulation
Process Principle:
Using sand pumps to create negative pressure in the tremie pipe, this method generates strong upward flow with excellent cleaning efficiency.
Key Considerations:
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Requires professional operation
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Control flow rate in unstable formations
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Maintain proper slurry levels
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Manage waste slurry properly
4. Air Lift Reverse Circulation
Process Principle:
Compressed air injected into the tremie creates density differences, generating powerful upward flow for efficient sediment removal.
Key Considerations:
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Requires careful equipment configuration
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Prevent collapse in unstable formations
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Maintain proper slurry levels
5. Submersible Pump with Slurry Purifier System
Process Principle:
This innovative system combines submersible pumps with advanced purification equipment for large-diameter/deep piles, achieving efficient sediment removal with reduced environmental impact.
Key Considerations:
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Proper equipment matching
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Ensure system sealing
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Conduct pre-operation checks
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Monitor slurry levels
6. Drilling Tool Cleaning (Slurry-Free Method)
Process Principle:
Specialized cleaning buckets remove sediment directly, relying on optimized slurry for wall stability without conventional circulation.
Case Study:
Guoxin Financial Tower project (Shenzhen) utilized this method for φ1800-2600mm piles reaching 41m depth into weathered granite (75MPa strength), achieving 2-3 piles/day for φ2000mm piles and 2-2.5 days/pile for φ2600mm piles.
Key Considerations:
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Maintain proper slurry parameters
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Use appropriate cleaning bucket designs
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Optimize slurry management
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Minimize construction intervals
Comparative Analysis of Cleaning Methods
| Method | Suitable Scope | Equipment Complexity | Efficiency | Slurry Consumption |
|---|---|---|---|---|
| Direct Circulation | φ≤1.5m, Depth≤40m | Low | Low | Medium |
| Cyclone Circulation | φ≤1.5m, Depth≤40m | Medium | Medium | Medium |
| Pump Reverse | φ≥1.5m, Depth≤80m | High | High | High |
| Air Lift Reverse | φ≥1.5m, Depth≥100m | High | High | High |
| Submersible System | Large/deep piles | High | High | Medium |
| Tool Cleaning | All conditions | Low | Highest | Lowest |
Optimization Strategy for Cleaning Process Selection
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Match method to project requirements: Consider pile dimensions, geological conditions, and equipment availability.
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Small/shallow piles: Direct circulation methods generally suffice.
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Large/deep piles: Reverse circulation methods (pump or air lift) deliver superior results.
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Advanced equipment: Slurry purification systems significantly enhance efficiency and reduce environmental impact.
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Tool cleaning advantages: This emerging method minimizes equipment needs and maximizes efficiency when properly executed. Successful applications in major Shenzhen projects demonstrate its potential.
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Adapt to local conditions: Given the variability in Shenzhen’s rotary drilling contractors’ capabilities, method selection should account for actual technical proficiency. When tool cleaning cannot meet specifications, conventional circulation methods must be supplemented.
By implementing these optimized sediment control strategies, rotary drilling pile construction can achieve higher quality standards while improving efficiency and cost-effectiveness.
