Introduction
Jet grouting is a high-pressure ground improvement technique capable of transforming in-situ soil into a cemented, strengthened mass. It is renowned for its versatility in a wide range of soil types and urban environments where access, precision, and performance are critical. Used for excavation support, liquefaction mitigation, seepage control, and foundation enhancement, jet grouting is a key technology in modern geotechnical engineering.
What is Jet Grouting?
Jet grouting involves the injection of a cementitious grout into the ground at very high pressures (typically 300–600 bar) through small-diameter nozzles located at the end of a drill rod. The high-velocity jet erodes the surrounding soil and mixes it in place with grout, forming a soil-cement column or mass with improved mechanical properties.
Jet Grouting Systems
Jet grouting is typically classified into three types based on the number and function of the injection jets:
1.Single Fluid System
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- Grout only
- Used in soft soils like silts or clay where minimal erosion is needed
2.Double Fluid System
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- Grout + air
- Air jet assists in expanding the treatment diameter
3.Triple Fluid System
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- Grout + air + water
- Used for granular or dense soils requiring aggressive erosion and mixing
Key Applications
- Excavation Support: Constructing impermeable soilcrete walls around deep excavations.
- Underpinning: Stabilizing and strengthening existing foundations without excavation.
- Liquefaction Mitigation: Increasing shear strength and stiffness in loose sands.
- Cutoff Walls: Forming impermeable barriers to prevent groundwater flow near dams, tunnels, and shafts.
- Tunnel Support: Pre-reinforcing weak soils ahead of tunnel boring operations.
Advantages of Jet Grouting
- Soil Independence: Works in nearly all soil types, from silts to gravels and some soft rock.
- Flexible Geometry: Can create columns, panels, or block masses tailored to site needs.
- Minimal Surface Disruption: Suitable for congested urban environments.
- Precise Control: Diameter, strength, and depth of treatment can be customized.
- Rapid Strength Gain: Soilcrete typically reaches design strength within 7–28 days.
Design and Execution
1.Site Investigation
- Soil classification, permeability, and strength parameters are essential.
- Trial grouting is often conducted to calibrate erosion rates and mixing efficiency.
2.Column Configuration
- Typical diameters range from 0.6 m to 2.0 m.
- Treatment depth can reach over 30 meters.
3.Grout Mix
- Portland cement-based, often with additives for set time and flowability.
- Water-cement ratios from 0.5 to 1.5 depending on soil and application.
4.Monitoring and Quality Control
- Real-time monitoring of pressure, flow rate, rotation speed, and lift rate.
- Core sampling and unconfined compressive strength (UCS) testing for verification.
Case Studies
1.Underground Station Shaft – Milan, Italy
Challenge: Constructing a 20-meter-deep shaft in sandy soil with a high water table.
Solution: Jet grouting was used to create a water-tight soilcrete wall and bottom plug.
Outcome: Allowed dry excavation without dewatering. No observable settlement in nearby buildings.
2.Foundation Underpinning for Heritage Building – Istanbul, Turkey
Challenge: Structural settlement in a 19th-century masonry structure built on variable fill.
Solution: Jet grout columns were installed beneath footings without excavation.
Outcome: Building stabilized with less than 1 mm of post-treatment movement. Preservation efforts continued safely.
Limitations
- Not effective in highly cemented soils or massive rock.
- Requires specialized equipment and experienced personnel.
- Costlier than some alternative methods, though often justified by performance and precision.
Conclusion
Jet grouting is one of the most adaptable and powerful ground improvement techniques available today. Its ability to stabilize, reinforce, and seal a broad range of soils makes it especially valuable in dense urban settings and complex geotechnical scenarios. When properly designed and executed, jet grouting delivers high-performance, durable, and precise results across a wide spectrum of geotechnical engineering challenges.
