Introduction
Permeation grouting is a ground improvement technique in which low-viscosity grouts (such as microfine cement, sodium silicate, or chemical grouts) are injected into porous soils to increase strength, reduce permeability, and improve stability. While short-term benefits are well documented, the durability and long-term performance of permeation grouted soils are critical for the safety and sustainability of geotechnical projects, especially in urban construction, tunneling, and foundation engineering.
Factors Affecting Long-Term Behavior
1. Grout Material Properties
- Cement-based grouts generally provide long-term strength and chemical stability but may undergo shrinkage and microcracking in aggressive environments.
- Chemical grouts (e.g., polyurethane, acrylamide, sodium silicate) offer excellent initial penetration but may degrade over decades due to chemical reactions or leaching.
2. Soil–Grout Interaction
- Bonding between grout and soil particles determines strength and permeability reduction.
- In coarse sands and gravels, cementitious grout forms durable stone-like matrices.
- In silty or clayey soils, effectiveness is lower, and long-term performance depends on grout penetration efficiency.
3. Environmental Exposure
- Aggressive groundwater containing sulfates, chlorides, or acids can cause grout degradation.
- Freeze–thaw cycles may induce cracking and loss of bond.
- Biological activity (e.g., bacterial degradation of organic grouts) may impact chemical grout durability.
4. Stress and Load Conditions
- Sustained loads, cyclic loading (traffic, rail vibrations), or seismic activity influence the microstructure of grouted soils.
- Long-term creep and settlement must be considered in design.
Observed Long-Term Performance
1. Strength Retention
- Cement-based permeation grouts typically retain 70–90% of their compressive strength over decades when protected from severe chemical attack.
- Chemical grouts may show gradual strength loss due to aging, shrinkage, or leaching.
2. Permeability Control
- Reduction in permeability is one of the most durable benefits, often persisting for decades, particularly with cementitious grouts.
- However, cracks induced by stress or shrinkage may gradually increase permeability.
3. Case Evidence
- Urban Tunnels (Shenzhen, China): Grouted soils around metro tunnels maintained stability for over 15 years, with minimal settlement recorded.
- Dam Foundations (Japan): Cement-based permeation grouting has shown consistent seepage reduction for over 30 years.
- Urban Excavations (Europe): Some chemical grouts showed partial loss of efficiency after 10–15 years, requiring supplementary injections.
Strategies to Enhance Durability
- Material Selection: Use sulfate-resistant cement or chemically stable grouts for aggressive environments.
- Hybrid Grouting: Combine cement-based and chemical grouts to balance penetration and long-term stability.
- Quality Control: Monitor injection pressure, grout take, and distribution to avoid voids and ensure complete permeation.
- Protective Measures: Incorporate drainage and barrier systems to minimize exposure to aggressive groundwater.
- Monitoring and Maintenance: Periodic settlement monitoring, permeability testing, and supplementary grouting when required.
Conclusion
The durability of permeation grouted soils depends on the interplay of grout type, soil properties, environmental exposure, and loading conditions. Cementitious grouts generally provide robust, long-lasting improvements, while chemical grouts excel in penetration but may require maintenance or re-injection for extended service life. With proper design, material selection, and monitoring, permeation grouting can provide reliable soil improvement for several decades, supporting safe and sustainable geotechnical infrastructure.
