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Slurry Wall Bored Pile Construction: Process, Methods, and Quality Control

Introduction to Slurry Wall Bored Piles

Slurry wall bored piles utilize drilling mud to stabilize borehole walls during mechanical drilling. This method circulates slurry to suspend and remove cuttings, making it suitable for both water-bearing and dry soil layers.

Key Construction Equipment

  • Submersible drilling rigs
  • Impact drilling rigs
  • Grab drills

Construction Process Flow

  1. Pile positioning survey
  2. Installation of casing pipe
  3. Drilling rig setup
  4. Slurry preparation
  5. Mechanical drilling (submersible/impact rig)
  6. Slurry circulation for cuttings removal
  7. Hole cleaning
  8. Reinforcement cage installation
  9. Underwater concrete pouring

I. Casing Installation and Slurry Preparation

1. Casing Pipe Installation

  • Excavate surface soil at pile location
  • Install 2m high steel casing (4-8mm thickness) with 200mm larger diameter than drill bit
  • Includes 1-2 overflow holes at top
  • Functions: Position fixing, hole protection, water pressure maintenance, and drill guidance

2. Slurry Preparation

  • Use 1.1-1.5 specific gravity slurry to:
    • Seal pore spaces in borehole walls
    • Maintain hydrostatic pressure
    • Stabilize borehole walls
    • Suspend and transport cuttings

II. Drilling Methods

1. Submersible Drilling Rig

Equipment Components:

  • Waterproof motor and drill bit assembly
  • Casing pipe
  • Mud circulation system

Working Principle:

  • Sealed drill unit operates underwater/inslurry
  • Two cuttings removal methods:

a) Direct Circulation:

  • High-pressure slurry pumps cuttings upward through overflow

b) Reverse Circulation:

  • Submersible pump directly extracts cuttings

2. Impact Drilling

Equipment Features:

  • Uses cross-shaped impact hammer (3-4t)
  • Free-fall mechanism fractures rock/soil

Construction Tips:

  • Initial 0.4-0.8m stroke with dense impacts
  • Gradually increase to 1.5-2.0m stroke
  • Maintain slurry density monitoring

III. Hole Cleaning (Desanding)

  • Inspect hole dimensions with detectors
  • Cleaning methods:
    • Air lift (0.5MPa pressure) for stable holes
    • Slurry circulation for unstable formations
  • Target slurry density: 1.15-1.25

IV. Underwater Concrete Pouring

  • Use higher-grade concrete (one class above design)
  • Tremie pipe method essentials:
    • Initial concrete volume sufficient for 0.8m embedment
    • Continuous pouring without interruption
    • Maintain positive pressure head

V. Common Quality Issues & Solutions

1. Necking

Causes:

  • Rapid extraction in soft soils
  • Insufficient concrete pressure

Solutions:

  • Maintain high concrete level in pipe
  • Control extraction speed (≤1m/min)
  • Use redrilling technique

2. Broken Piles

Prevention:

  • Minimum 4D pile spacing
  • Jump sequencing construction

3. Soft Toe Defects

Countermeasures:

  • Initial slow extraction with re-driving
  • Quality casing-seal interfaces

4. Excessive Concrete Use

Indicates:

  • Underground cavities
  • Soil expansion in soft strata

Response:

  • Conduct test piles in soft ground
  • Consider alternative pile types

Construction Best Practices

  • Strict slurry density control
  • Continuous concrete pouring
  • Real-time drilling parameter monitoring
  • Post-construction integrity testing

This comprehensive guide covers slurry wall bored pile construction from equipment selection to quality troubleshooting, ensuring reliable deep foundation implementation for various ground conditions.

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