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:
- Single-Fluid System (Single-Tube Method)
- Uses a single injection pipe to eject cement slurry.
- 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.
- 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:
- High-pressure jet cutting – Disrupts soil structure, forming cavities.
- Mixing & stirring – Combines soil and slurry into a new matrix.
- Lift replacement (Triple-Tube Method) – Compressed air removes cuttings, replaced by slurry.
- Filling & permeation – Slurry fills voids and solidifies.
- 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
- 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.
- 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.
