Introduction
Rock fissure grouting is a common ground improvement technique used to seal cracks, reduce permeability, and improve stability in fractured rock masses. It is widely applied in dams, tunnels, foundations, and slopes. The effectiveness of grouting depends on the geological conditions, including fracture patterns, groundwater presence, and rock strength. This article evaluates the performance of rock fissure grouting under varying geological settings.
Factors Influencing Performance
- Fracture Aperture and Connectivity – Determines how far and effectively grout can penetrate.
- Groundwater Flow – High inflows may dilute or wash away grout, affecting results.
- Rock Strength and Weathering – Weak or weathered rocks absorb grout differently than intact rocks.
- Grout Properties – Viscosity, setting time, and durability must match geological conditions.
Performance in Different Geological Conditions
1. Massive, Slightly Fractured Rock
- Behavior: Limited joints with moderate apertures.
- Performance: Very effective, as grout easily fills major discontinuities.
- Best Materials: Cement-based or microfine cement grouts.
2. Moderately Fractured Rock
- Behavior: Combination of large fractures and small cracks.
- Performance: Good, if staged grouting is applied (first for large fissures, then for finer cracks).
- Best Approach: Hybrid strategy using cement and microfine or chemical grouts.
3. Highly Fractured or Weathered Rock
- Behavior: Numerous interconnected micro-cracks and high permeability.
- Performance: Moderate, as cement grouts may not penetrate well; requires low-viscosity materials.
- Best Materials: Microfine cement or chemical grouts for better penetration.
4. Karstic or Cavernous Rock
- Behavior: Large voids and irregular cavities.
- Performance: Challenging; requires high grout volumes and repeated injections.
- Best Approach: Stage grouting with bulk cement mixes for large voids.
5. Fault Zones and Shear Zones
- Behavior: Filled with soft gouge, highly unstable.
- Performance: Difficult; grout may be carried away or fail to bond.
- Best Approach: Use of stabilizing chemical grouts, combined with mechanical supports.
6. Aggressive Groundwater Conditions
- Behavior: Sulfate-rich or acidic environments may damage grout.
- Performance: Depends on material durability.
- Best Materials: Sulfate-resistant cement or chemically stable grouts.
Evaluation Methods
- Packer (Lugeon) Tests: Measure permeability before and after grouting.
- Grout Take Records: Track grout volumes and pressure to assess penetration.
- Water Inflow Monitoring: Check reduction in seepage rates.
- Core Sampling: Confirms grout filling in fractures.
Conclusion
The performance of rock fissure grouting is highly dependent on geological conditions.
- Best results occur in massive to moderately fractured rocks with controlled groundwater flow.
- Weathered, karstic, and faulted zones require more advanced materials and staged techniques.
- Careful material selection, pressure control, and monitoring are essential for achieving durable and effective results.
Rock fissure grouting remains a versatile and reliable method, but success lies in tailoring the approach to the specific geological environment.
