Compaction grouting is a highly effective ground improvement technique used to densify loose or weak soils and control settlement without excavating or disturbing overlying structures. By injecting stiff, low-mobility grout under pressure, this method displaces surrounding soil, increasing its density and stiffness. In recent decades, it has proven instrumental in both infrastructure and industrial projects, including under railways, highways, storage tanks, and sensitive facilities. This article presents the working principles of compaction grouting along with real-world case studies and practical best practices.
1.What is Compaction Grouting?
Compaction grouting—also called low-mobility grouting—involves the injection of a thick, mortar-like grout (usually a cement-sand or fly ash mix) into soil to physically displace and compact it. Unlike permeation or jet grouting, the grout does not permeate the soil matrix; instead, it forms discrete bulbs that densify the surrounding ground.
Key goals:
- Densification of loose granular soils,
- Mitigation of settlement (existing or anticipated),
- Foundation support for new or existing structures,
- Sinkhole remediation and void filling.
2.Process and Materials
Grouting Process
- Boreholes are drilled vertically or at an angle to target zones.
- Grout is injected from the bottom-up in stages (typically 0.3–1.5 m).
- Pressure and volume are monitored to control bulb formation.
- Multiple injection points may be required based on area and depth.
Grout Characteristics
- High-viscosity, low-slump (25–75 mm) mix.
- Common materials: Portland cement, sand, fly ash, water-reducing admixtures.
- Flow is minimal to prevent soil migration or hydrofracturing.
3.Case Studies
Case Study 1: Stabilization Beneath a Highway Embankment
Location: Eastern India
Problem: Embankment settlement up to 180 mm over 18 months due to loose alluvial sand.
Solution:
- Compaction grouting at depths of 3–8 m using a 300 mm grid.
- Grout injected at 0.5 m stages from the base upward.
- Average grout take: 2.8 m³ per point.
Result:
- Surface settlement halted.
- Embankment re-leveled using controlled lifting.
- Long-term monitoring showed <5 mm settlement over the next two years.
Case Study 2: Factory Floor Leveling in an Operational Industrial Plant
Location: Tamil Nadu
Problem: Uneven factory floor with 40 mm differential settlement affecting CNC equipment alignment.
Solution:
- Compaction grout delivered through angled boreholes beneath the slab.
- Precision lifting of floor achieved using real-time level sensors.
- Grouting work conducted during non-production hours to avoid disruption.
Result:
- Floor brought back to level with <2 mm deviation.
- Production resumed without requiring slab replacement or downtime.
Case Study 3: Sinkhole Remediation at a Power Substation
Location: Coastal Maharashtra
Problem: Karstic limestone led to subsidence beneath transformer pads.
Solution:
- Compaction grout used to fill voids and densify surrounding soil.
- Boreholes grouted down to 12 m depth, forming a 3D bulb network.
- Seismic tests confirmed increase in shear wave velocity post-treatment.
Result:
- Ground stabilized with no further subsidence reported.
- Equipment reinstalled without relocating the facility.
4.Benefits of Compaction Grouting
| Benefit | Explanation |
| Minimal Surface Disturbance | Ideal for developed or active sites (plants, roads, tunnels). |
| Control of Existing Settlement | Used to lift and relevel structures without excavation. |
| No Vibration or Excavation | Does not disturb sensitive equipment or foundations. |
| Targeted Ground Densification | Delivers strength where needed without affecting surroundings. |
| Void Filling | Effective in karstic zones and under slabs, tanks, culverts. |
5.Limitations and Considerations
| Limitation | Mitigation Strategy |
| Requires skilled operation | Operator training and close monitoring of injection parameters. |
| Difficult in dense or cohesive soils | Best suited to granular soils; may require pre-drilling. |
| Pressure-induced heave | Monitor and limit injection pressure to avoid surface damage. |
| Not suitable for permeation objectives | Use chemical or cement grouts if seepage control is needed. |
Instrumentation and response monitoring are essential for successful application.
6.Best Practices for Successful Compaction Grouting
- Pre-grouting investigation: CPTs, borehole logs, and geophysical surveys to identify target zones.
- Grout mix design testing: Confirm pumpability and expansion characteristics.
- Bottom-up staging: Ensures full zone coverage and minimizes blowouts.
- Real-time monitoring: Pressure, volume, and heave sensors to prevent over-injection.
- Post-treatment testing: Conduct soil density and shear strength checks.
Conclusion
Compaction grouting is a proven solution for stabilizing and releveling infrastructure and industrial foundations affected by weak or loose soils. Its adaptability and low-impact nature make it a preferred method in urban, industrial, and operational settings, where precision, safety, and minimal disruption are critical.
As more aging structures require rehabilitation and new facilities are built on marginal ground, compaction grouting continues to be an indispensable technique—bridging geotechnical reliability with construction flexibility.
