Introduction
Fractured rock formations often present challenges such as excessive groundwater inflow, reduced stability, and increased permeability, especially in tunneling, dam foundations, and underground excavations. Two widely adopted techniques to address these issues are rock fissure grouting and permeation grouting. While both methods aim to strengthen the rock mass and control seepage, their mechanisms, applications, and performance differ. This article provides a comparative study of the two methods, highlighting their design considerations, advantages, and limitations.
Rock Fissure Grouting
Rock fissure grouting is a targeted method that injects grout into natural discontinuities, such as joints, cracks, and fissures in the rock mass.
- Mechanism: Grout fills and seals discrete fissures, blocking water flow and improving rock strength.
- Materials: Cement-based grouts for wider fissures; microfine cement or chemical grouts for narrow cracks.
- Applications: Dam foundations, slope stabilization, and tunnels with significant water ingress through major fractures.
- Advantages:
- Directly seals large and open fissures.
- Provides structural reinforcement and bonding.
- Long-term durability when cementitious grouts are used.
- Limitations:
- Less effective for micro-cracks and very tight fracture networks.
- Requires precise drilling and mapping of fissures.
- Higher grout volumes and costs when fracture systems are extensive.
Permeation Grouting
Permeation grouting is designed to inject low-viscosity grout into small, interconnected voids and pores within the rock mass, without altering its structure.
- Mechanism: Grout permeates through micro-cracks and pores, reducing permeability and improving stiffness.
- Materials: Microfine cement and chemical grouts (silicates, polyurethane, acrylates) are commonly used.
- Applications: Weathered or fractured rock masses with fine cracks, underground structures requiring seepage control, and urban excavation sites.
- Advantages:
- Provides uniform treatment in micro-fissured zones.
- Effective in reducing overall permeability.
- Requires lower injection pressures, minimizing the risk of hydrofracturing.
- Limitations:
- Ineffective in sealing large, open voids.
- Chemical grouts may raise environmental and durability concerns.
- Requires strict quality control and monitoring.
Comparative Analysis
| Aspect | Rock Fissure Grouting | Permeation Grouting |
| Target Zone | Large fissures, joints, and cracks | Micro-cracks, porous or weathered zones |
| Grout Material | Cement, microfine cement, chemicals | Microfine cement, chemical grouts |
| Injection Pressure | Moderate to high, risk of hydrofracture if uncontrolled | Low, avoids creating new fractures |
| Applications | Dams, tunnels, slope stabilization | Urban foundations, underground works, seepage control |
| Advantages | Strong structural improvement, durable sealing | Uniform permeability reduction, effective for fine cracks |
| Limitations | Misses micro-cracks, higher costs in dense fracture systems | Cannot fill large voids, durability concerns with chemicals |
Conclusion
Both rock fissure grouting and permeation grouting are effective ground improvement methods for fractured rock, but their success depends on the nature of the rock mass and project requirements.
- Rock fissure grouting is best suited for large, open fractures and water channels, providing structural reinforcement.
- Permeation grouting is more effective in fine crack networks and weathered zones, reducing permeability uniformly.
In many complex projects, a combined approach—using fissure grouting for large cracks followed by permeation grouting for residual micro-cracks—offers the most reliable solution for long-term stability and seepage control.
