As construction advances into areas with increasingly complex subsurface conditions—loose fill, soft clays, and high groundwater tables—engineers require versatile, high-performance ground improvement solutions. Jet grouting has emerged as a premier technique for forming in-situ soil–cement columns that improve bearing capacity, stability, and seepage resistance for deep foundations. This article explores the principles of jet grouting, focusing on column formation mechanisms, quality control protocols, and real-world field performance.
1..What is Jet Grouting?
Jet grouting is a high-pressure grouting process that uses jets of grout, air, or water to break up and mix in-situ soil with a cementitious slurry. This creates a soilcrete column of predetermined diameter and strength.
Jet grouting is ideal when:
- Traditional piling is difficult due to variable soil layers,
- Space constraints limit access,
- There’s a need to treat soil beneath existing structures,
- High groundwater flow interferes with other ground improvement methods.
2.Column Formation Mechanisms
There are three primary systems used in jet grouting:
| System | Jet Configuration | Column Diameter Range |
| Single | Cement grout only | 0.3 – 1.0 m |
| Double | Grout + compressed air | 0.6 – 1.5 m |
| Triple | Grout + air + water | 0.8 – 2.5 m |
Key Formation Parameters
- Jet pressure: 400–600 bar for grout, 20–50 bar for air
- Nozzle size and rotation speed: Dictate the cutting radius
- Withdrawal rate: Determines uniformity of soilcrete
- Grout mix: Typically 0.5–1.5 water/cement ratio with additives
Columns can be installed vertically, inclined, or in panels, depending on application.
3.Applications in Deep Foundations
Jet grouting supports a range of deep foundation needs, including:
a) Load-Bearing Elements
- Forming isolated columns beneath spread footings or rafts in poor soil
- Increasing effective bearing capacity under towers, tanks, and silos
b) Excavation Support and Cutoff Walls
- Jet grout panels and curtains are used in deep excavations to form water-tight shoring systems
c) Seismic Retrofit
- Enhancing liquefaction resistance of loose granular soils
- Reinforcing slope toes and foundation bases
d) Underpinning Existing Structures
- Used where access is restricted, allowing columns to be formed without excavation
4.Quality Control in Jet Grouting
Jet grouting is highly sensitive to field parameters, so rigorous quality control is essential for success.
Pre-construction Testing
- Soil sampling and laboratory testing for jetability
- Field trial columns to confirm design diameter and strength
Execution Monitoring
- Real-time control of:
- Grout flow rate and pressure
- Nozzle rotation speed
- Lifting (withdrawal) rate
- Data logging for every column
Post-Construction Testing
- Core sampling of columns for unconfined compressive strength (UCS)
- Penetration testing (e.g., SPT, CPT) to assess improvement
- Ultrasonic or GPR scanning for integrity in large-diameter applications
Acceptance Criteria:
- UCS typically ranges from 1 to 5 MPa, depending on function
- Column continuity and diameter within ±10% of design
5.Field Performance: Case Studies
Case Study 1: Metro Station Underpinning
Location: Tier-1 city, India
Problem: Soft clay and old fill beneath future load-bearing walls
Solution:
- Installed triple-jet grout columns (1.2 m dia) to 15 m depth
- Overlapping columns formed continuous block beneath base slab
Result: - Achieved bearing capacity >400 kPa
- No differential settlement observed during or after construction
Case Study 2: Cutoff Wall for Deep Shaft
Location: Urban sewage tunnel project
Problem: High groundwater inflow in coarse sand and gravel
Solution:
- Jet grout panels formed a 2 m thick vertical curtain around 25 m deep shaft
- Double-jet system used for wider spread
Result: - Reduced seepage by 90%
- Shaft excavation completed safely without dewatering complications
Case Study 3: Liquefaction Mitigation for Oil Tank Farm
Location: Coastal refinery site
Problem: Liquefaction-prone sands beneath 30 m diameter tanks
Solution:
- Grid of jet grout columns (1 m dia, 12 m deep) beneath tank bases
- Columns spaced at 2.5 m centers in triangular pattern
Result: - Post-treatment CPT showed 3x increase in tip resistance
- Foundation performance validated through monitoring during minor seismic activity
6.Advantages of Jet Grouting
| Advantage | Explanation |
| Applicable in all soil types | Works in sand, silt, clay, gravel, and even weathered rock |
| Minimal surface disruption | Ideal in urban or restricted-access projects |
| Excellent seepage control | Soilcrete is low permeability (~10⁻⁸ m/s) |
| Custom geometry | Can form columns, panels, blocks, or arcs as needed |
| High strength and durability | UCS can be tailored through mix design and curing |
7.Limitations and Considerations
| Limitation | Mitigation Strategy |
| High equipment and material cost | Use only where other methods are not viable |
| Not suitable for highly permeable gravel zones | Reduce with pre-grouting or switch to double/triple jet systems |
| Spoil management | Requires safe disposal of spoil slurry |
| Column shape variability | Use test columns and proper monitoring to ensure consistency |
Conclusion
Jet grouting offers unmatched flexibility and effectiveness for deep foundation improvement, especially in complex or constrained sites. By creating robust soilcrete columns with excellent strength and permeability properties, it provides both structural support and hydraulic control. When designed carefully and executed with proper quality control, jet grouting delivers reliable long-term performance for even the most demanding projects.
As cities densify and critical infrastructure is built on challenging ground, jet grouting will remain a key innovation—blending power, precision, and adaptability in deep foundation engineering.
