Introduction
Urban development projects often demand construction in challenging soil and groundwater conditions, where conventional foundation and support methods alone may not be sufficient. Jet grouting, a versatile ground improvement technique, is increasingly integrated with deep foundation systems and excavation support structures to enhance stability, control groundwater, and improve bearing capacity. This integration provides cost-effective and technically robust solutions for high-rise buildings, underground structures, and metro systems.
Role of Jet Grouting in Foundation and Excavation Projects
Jet grouting is applied as secondary ground improvement to complement primary structural systems. Its functions include:
- Soil Strengthening: Creating soilcrete columns that improve load-bearing capacity.
- Permeability Control: Reducing groundwater inflow through cutoff walls or bottom plugs.
- Settlement Mitigation: Densifying weak soils beneath or adjacent to foundations.
- Excavation Stability: Forming barriers or reinforced blocks to resist lateral soil pressure.
Integration with Deep Foundations
- Pile Foundations
- Application: Jet grouting around or beneath piles enhances end-bearing capacity and reduces negative skin friction.
- Benefits:
- Improved pile group efficiency.
- Reduced settlement in soft or liquefiable soils.
- Increased lateral resistance when combined with bored piles.
- Example: In soft clay sites, jet grout columns installed beneath pile tips provide an artificial bearing stratum.
- Raft Foundations
- Application: Jet grouting beneath rafts (so-called “jet-grout rafts”) creates a stiffened layer that distributes loads uniformly.
- Benefits:
- Enhanced bearing capacity.
- Mitigation of differential settlement.
- Reduction in required raft thickness and reinforcement.
- Micropiles and Underpinning
- Application: Jet grouting combined with micropiles provides composite action, where piles carry concentrated loads while soilcrete distributes stresses.
- Benefits:
- Useful in retrofitting and upgrading existing foundations.
- Enables load transfer in historic or sensitive structures without significant vibration.
Integration with Excavation Support Systems
- Diaphragm and Secant Pile Walls
- Application: Jet grout columns can seal joints between panels or piles to prevent groundwater inflow.
- Benefits:
- Effective cutoff against water ingress.
- Increases lateral stiffness of retaining walls.
- Provides continuity in mixed ground conditions.
- Bottom Seals and Plugs
- Application: Jet grouting forms impermeable and high-strength horizontal plugs beneath excavations.
- Benefits:
- Prevents basal heave in soft clays.
- Controls groundwater inflow in deep shafts.
- Provides safe working conditions during construction of metro stations and basements.
- Ground Arching and Block Systems
- Application: Jet grout columns arranged in block or arch configurations act as temporary or permanent excavation supports.
- Benefits:
- Minimizes ground movements in urban tunneling.
- Creates load-bearing vaults above underground structures.
Design Considerations
- Column Layout: Depends on structural requirements (grid, block, wall, or plug arrangement).
- Column Diameter and Overlap: Designed to ensure continuity and watertightness.
- Strength Requirements: Soilcrete compressive strength typically 2–10 MPa depending on function (structural support vs. seepage cutoff).
- Groundwater Conditions: Additional measures (e.g., anti-washout admixtures) required in high-flow zones.
- Interaction with Structural Elements: Jet grout must be positioned to complement piles, rafts, or walls without inducing excessive stresses.
Case Applications
- Metro Station Excavation in Soft Clay (Asia)
- Jet grout bottom plugs combined with diaphragm walls enabled safe dry excavation below groundwater table.
- High-Rise Building Foundation (Europe)
- Jet grouting beneath raft foundation reduced settlements and enhanced overall bearing capacity.
- Historic Structure Underpinning (Italy)
- Jet grout columns integrated with micropiles stabilized the foundation without disturbing the structure above.
Advantages of Integration
- Technical: Improved soil-structure interaction, reduced deformations, and enhanced safety in deep excavations.
- Economic: Reduction in structural member sizes and material costs by improving ground performance.
- Environmental: Less reliance on dewatering, reduced vibrations compared to alternative methods.
Conclusion
The integration of jet grouting with deep foundations and excavation support systems provides a powerful geotechnical solution for modern construction challenges. By combining soilcrete reinforcement with structural elements, engineers achieve greater stability, improved load capacity, and effective groundwater control. With advancements in jet grouting technology, such hybrid systems will continue to play a crucial role in sustainable and resilient urban infrastructure development.
