Introduction
Compaction grouting is a widely adopted ground improvement technique that involves the injection of a low-mobility, high-viscosity grout into loose or soft soils to densify the ground, fill voids, and enhance bearing capacity. It is particularly effective in sandy, silty, or collapsible soils, where conventional foundations may suffer from settlement or instability. Evaluating the performance of compaction grouting is critical to ensure that the treated soil meets the required engineering objectives and provides long-term stability.
Key Performance Indicators
1. Soil Densification
- Grouting creates discrete grout bulbs that displace and compact surrounding soil.
- Densification is typically measured by in-situ density tests such as Standard Penetration Test (SPT) or Cone Penetration Test (CPT) before and after grouting.
- In loose sands, improvement ratios of 20–50% increase in density are commonly observed.
2. Settlement Reduction
- Compaction grouting reduces potential settlement under applied loads.
- Plate load tests and settlement monitoring on treated zones quantify the reduction.
- Properly executed grouting can reduce settlement in soft clay and silt layers by 30–70%, depending on soil conditions and grout pattern.
3. Load-Bearing Capacity
- Treated soils exhibit increased bearing capacity, supporting heavier foundations without excessive settlement.
- Performance is assessed through static or dynamic load tests.
- For granular soils, bearing capacity may increase by 50–100%, improving foundation safety margins.
4. Lateral and Shear Resistance
- Compaction grouting enhances lateral resistance in loose soils, which is critical for retaining walls, embankments, and slope stabilization.
- Shear tests and monitoring of wall deflections or slope movements confirm improvements.
5. Permeability Control
- While primarily designed for densification, compaction grouting can reduce permeability locally, mitigating seepage in granular soils.
- Permeability tests post-grouting confirm the extent of water flow reduction.
Factors Influencing Performance
1. Soil Type and Condition
- Loose, cohesionless soils respond better to compaction grouting.
- Soft clays and silts may require staged injections to avoid heave.
2. Grout Properties
- Low-mobility, high-viscosity cementitious grout ensures bulb formation without excessive migration.
- Additives can improve strength, reduce shrinkage, and enhance durability.
3. Injection Design
- Hole spacing, injection depth, and sequencing must be optimized to achieve uniform soil improvement.
- Staged injections minimize surface heave and uneven compaction.
4. Monitoring and Quality Control
- Real-time monitoring of injection pressure, volume, and soil movement ensures successful performance.
- Post-grouting verification through density tests, load tests, and settlement measurements validates effectiveness.
Case Examples
Loose Sandy Soil
- Grouting beneath a shallow foundation increased SPT values from 10 to 18–20 blows/ft.
- Settlement under a design load decreased by 45%, confirming improved stiffness and bearing capacity.
Soft Silt Layer
- Staged injection created overlapping grout bulbs, densifying silt and preventing excessive heave.
- Plate load tests showed a 60% increase in ultimate bearing capacity.
Urban Pavement Remediation
- Voids beneath a road embankment were filled with compaction grout, restoring surface elevation.
- Post-grouting monitoring revealed minimal residual settlement, improving ride quality and longevity.
Conclusion
Compaction grouting is highly effective for improving loose and soft soils, enhancing density, reducing settlement, and increasing load-bearing capacity. Performance evaluation through in-situ testing, monitoring, and post-grouting verification ensures that the ground meets design requirements. Proper grout selection, injection design, and quality control are essential to achieve optimal results, making compaction grouting a reliable solution for challenging geotechnical conditions.
