Introduction
Tube-à-Manchette (TAM) grouting has become a cornerstone in ground improvement, seepage control, and structural reinforcement for underground and geotechnical works. While its short-term performance in stabilizing soils and reducing permeability is well established, questions often arise regarding its durability and long-term effectiveness, especially in aggressive environments such as chemically aggressive soils, high groundwater pressures, saline conditions, or areas with cyclic loading.
This article examines the factors influencing the longevity of TAM grouting, mechanisms of degradation, and strategies to ensure sustainable performance.
1. Factors Influencing Durability of TAM Grouting
1.1 Environmental Aggressiveness
- Chemical Attack: Sulfates, chlorides, and acidic groundwater may deteriorate cement-based grout.
- Salinity: In coastal and marine environments, chloride ingress can compromise grout strength.
- Biological Activity: Microbial-induced corrosion can weaken grout in organic-rich soils.
1.2 Mechanical Stresses
- Cyclic Loads: From traffic or seismic activity can induce microcracks in hardened grout.
- Ground Movements: Settlement or heave may disrupt grout-soil bonding.
1.3 Grout Composition
- Use of ordinary Portland cement (OPC) may be less durable than modified mixes containing silica fume, fly ash, or slag.
- Chemical grouts (e.g., silicates, acrylates, polyurethane) vary in resistance depending on the aggressiveness of the environment.
2. Mechanisms of Long-Term Degradation
- Leaching: Groundwater flow can wash out soluble compounds, reducing grout density.
- Chemical Reactions: Sulfate attack can lead to expansive ettringite formation, causing cracking.
- Shrinkage and Cracking: Poorly designed grout mixes may shrink, creating seepage pathways.
- Bond Deterioration: Over time, soil-grout interfaces may weaken, especially in loose sands or soft clays.
3. Case Study Insights
3.1 Metro Tunnels in Aggressive Groundwater (Europe)
- TAM grout curtains around diaphragm walls were exposed to high-sulfate groundwater.
- After 15+ years, core sampling showed slight reduction in compressive strength but maintained impermeability.
- Use of sulfate-resistant cement proved critical.
3.2 Coastal Underground Car Parks (Asia)
- TAM grouting provided groundwater cutoff against saline intrusion.
- After 10 years, chemical analysis revealed chloride penetration, but performance remained satisfactory due to low-permeability grout mix.
3.3 Hydropower Caverns (South America)
- TAM grouting in fractured rock subjected to high-pressure seepage.
- Monitoring over two decades showed stable seepage control, demonstrating long-term grout-rock bonding effectiveness.
4. Strategies to Enhance Long-Term Effectiveness
4.1 Material Selection
- Use of sulfate-resistant cement or blended cements (with slag/fly ash).
- Incorporation of microfine cement for improved penetration and durability.
- For extreme environments, chemical grouts (polyurethane, silicate) may outperform cement-based options.
4.2 Quality Control During Execution
- Strict control of grouting pressures and volumes to avoid fractures and washouts.
- Real-time monitoring to verify grout spread and penetration.
4.3 Protective Design Measures
- Redundancy in design, e.g., multiple grout curtains for seepage control.
- Integration with cutoff walls, piles, or liners for composite action.
- Regular monitoring and maintenance through piezometers, permeability tests, and borehole inspections.
5. Long-Term Performance Outlook
- Well-designed TAM grouting systems can remain effective for decades, even under aggressive conditions.
- Performance depends heavily on initial mix design, execution quality, and environmental exposure.
- When properly implemented, TAM grouting ensures sustainable seepage control, soil stabilization, and structural safety in demanding geotechnical projects.
Conclusion
The durability and long-term effectiveness of TAM grouting in aggressive environments rely on a careful balance of grout material selection, site-specific design, and execution precision. While chemical and mechanical degradation mechanisms exist, evidence from global case studies shows that with sulfate-resistant or modified grout mixes, strict quality control, and periodic monitoring, TAM grouting can provide decades of reliable performance in harsh underground conditions.
