High-Pressure Jet Grouting: Techniques, Process, and Quality Control

Introduction to High-Pressure Jet Grouting

High-pressure jet grouting is an advanced ground improvement technique that strengthens soil or creates waterproof barriers. The process involves drilling a grouting pipe with a nozzle to a predetermined depth, then ejecting a high-pressure (20–40 MPa) fluid (cement slurry, water, or air) to cut, disturb, and mix with the soil. As the drill rod is gradually lifted, the slurry solidifies into a cylindrical column (jet grouted pile), enhancing soil stability or preventing water seepage.

Jet Grouting Methods

Depending on the injection technique, jet grouting can be classified into three methods:

1. Single-Fluid System (Single-Tube Method)
   • Uses a single injection pipe to eject cement slurry.
2. Double-Fluid System (Dual-Tube Method)
   • Simultaneously injects high-pressure cement slurry and compressed air.
   • The combined action of slurry and air significantly increases soil disruption, forming a larger consolidated column.
3. Triple-Fluid System (Triple-Tube Method)
   • Utilizes separate pipes for water, air, and cement slurry.
   • High-pressure water and air cut the soil, creating voids, while low-pressure slurry fills the gaps.
   • Produces columns up to 2m in diameter.

Factors Affecting Jet Grouting Efficiency

The consolidation radius depends on:

• Directly proportional factors: Injection pressure (P), nozzle diameter (d).
• Inversely proportional factors: Lifting speed (S), soil shear strength (τ), slurry density (B).

Column strength is determined by cement content and soil properties.

Jet Grouting Mechanism

The process involves five key actions:

1. High-pressure jet cutting – Disrupts soil structure, forming cavities.
2. Mixing & stirring – Combines soil and slurry into a new matrix.
3. Lift replacement (Triple-Tube Method) – Compressed air removes cuttings, replaced by slurry.
4. Filling & permeation – Slurry fills voids and solidifies.
5. Compaction – Residual pressure densifies the surrounding soil.

Construction Process & Key Steps

1. Pre-Construction Preparation

• Conduct supplementary geological surveys.
• Ensure high-quality cement (e.g., Type 425 Portland) and clean water (pH 5–10).
• Perform lab mix design tests (water-cement ratio: 1.0–1.5) with additives (e.g., lignin, gypsum).
• Conduct trial piles to refine parameters (lifting speed, rotation speed, pressure).
• Clear and level the site, set up drainage and slurry pits.
• Mark pile locations with stakes.

2. Construction Procedure

• Drill positioning: Align and level the rig (verticality tolerance ≤1–1.5%).
• Slurry preparation: Mix cement, water, and additives; filter through 0.8mm screens.
• Drilling (Triple-Tube): Drill to design depth (150mm pre-bore).
• Pipe insertion (Single/Double-Tube): Use vibration or jetting to embed the pipe.
• Lifting & mixing: Apply design pressure (20–40 MPa), rotate, and lift at a controlled rate.
• Pile head treatment: Slow lifting near the top (1m below) to ensure quality.
• Gravelly soil adjustment: Repeat jetting if necessary.
• Equipment cleaning: Flush pipes after each pile.
• Backfilling: Address shrinkage cracks with 1.0 water-cement ratio slurry.

3. Recommended Parameters

Method	Slurry Pressure	Air Pressure	Water Pressure	Lifting Speed	Rotation Speed
Single-Tube	20–40 MPa	–	–	0.2–0.25 m/min	20 rpm
Double-Tube	20–40 MPa	0.7–0.8 MPa	–	As tested	As tested
Triple-Tube	0.2–0.8 MPa	0.5–0.8 MPa	30–50 MPa	As tested	As tested

Quality Control Measures

1. Key Requirements
   • Ensure trial piles validate parameters.
   • Limit slurry loss (<20% of injected volume).
   • Maintain continuous rotation/lifting (10–20cm overlap at joints).
   • Use fresh cement; filter slurry to prevent nozzle clogging.
2. Troubleshooting
   • Low slurry return: Increase density, add sand/clay, or use sealing balls.
   • Excessive slurry return: Raise pressure, reduce nozzle size, or accelerate lifting.
   • Surface voids: Secondary grouting with expansive mixes (e.g., cement + water + aluminum powder).

Safety & Environmental Considerations

• Safety:
  • Inspect high-pressure equipment regularly.
  • Maintain ≥60cm clearance from active nozzles.
  • Handle chemicals with care (eye protection required).
• Environmental:
  • Cover cement/lime during storage/transport.
  • Implement dust suppression and noise control.
  • Properly dispose of waste slurry.

Conclusion

High-pressure jet grouting is a versatile solution for soil stabilization and waterproofing. By optimizing parameters and adhering to strict quality controls, engineers can achieve durable, high-performance ground improvements. For specialized applications, consult a geotechnical expert to tailor the approach to site-specific conditions.