Thin Spray-on Liners (TSL) represent a revolutionary approach to underground support in mining and tunneling. These innovative products offer a lightweight, fast-applying alternative to traditional support methods, providing both safety and efficiency benefits in underground operations.
Definition and Characteristics of TSL
Thin Spray-on Liners are polymer-based products that are sprayed onto rock surfaces to form a thin (typically 3-5mm thick) but strong supportive membrane. Key characteristics include:
Rapid Setting: Most TSLs set within minutes to hours, allowing for quick return to work areas.
High Tensile Strength: Despite their thinness, TSLs offer significant tensile strength.
Flexibility: They can accommodate some ground movement without cracking.
Adhesion: Strong bonding to rock surfaces enhances support capabilities.
Water Resistance: Many TSLs provide excellent waterproofing properties.
Types of TSL
Polyurethane-based TSL: Offers high flexibility and rapid curing.
Polyurea-based TSL: Known for extreme durability and chemical resistance.
Methacrylate-based TSL: Provides good adhesion and fire-retardant properties.
Hybrid Systems: Combine properties of different polymer types for optimized performance.
Applications of TSL in Underground Support
Primary Support: In some less demanding conditions, TSL can serve as the primary support mechanism.
Secondary Support: Often used in conjunction with bolts and mesh for enhanced safety.
Weathering Protection: Prevents degradation of exposed rock surfaces.
Ventilation Improvement: Smooth surface reduces air resistance in tunnels and shafts.
Spalling Prevention: Helps contain loose rock and prevent small rock falls.
Advantages of TSL
Speed of Application: Can be applied much faster than traditional shotcrete.
Minimal Equipment: Requires less bulky equipment compared to shotcrete systems.
Reduced Rebound: Very little material waste during application.
Lightweight: Adds minimal dead load to the supported structure.
Corrosion Protection: Can protect steel supports and rock bolts from corrosive environments.
Limitations and Considerations
Cost: Initial material costs can be higher than traditional methods.
Long-term Performance: Less historical data compared to conventional support systems.
Application Conditions: Sensitive to surface moisture and cleanliness.
Training: Requires skilled operators for proper application.
Underground Concrete Support
While TSLs offer innovative solutions, traditional concrete support remains a cornerstone of underground construction and mining. Let's explore the various forms and applications of concrete support in underground environments.
Types of Underground Concrete Support
Shotcrete
Pneumatically applied concrete
Can be reinforced with fibers or mesh
Thickness typically ranges from 50mm to 200mm
Cast-in-place Concrete
Formed and poured on-site
Used for permanent, high-strength support
Common in large underground openings and shafts
Precast Concrete Segments
Manufactured off-site and assembled underground
Often used in conjunction with tunnel boring machines (TBMs)
Concrete Blocks and Pillars
Used for localized support in mining applications
Can be precast or cast in-situ
Application Methods for Underground Concrete
Wet-Mix Shotcrete
Most common in modern applications
Provides consistent quality and high output
Dry-Mix Shotcrete
Water added at the nozzle
Useful in areas with limited water supply
Form and Pour
Traditional method for cast-in-place concrete
Allows for precise shaping and reinforcement placement
Slip Forming
Continuous pouring method
Efficient for vertical structures like shafts
Reinforcement Techniques
Steel Fiber Reinforcement
Enhances tensile strength and crack resistance
Commonly used in shotcrete applications
Synthetic Fiber Reinforcement
Provides secondary reinforcement and plastic shrinkage control
Non-corrosive alternative to steel fibers
Welded Wire Mesh
Traditional reinforcement method
Can be combined with shotcrete or cast-in-place concrete
Rebar
Used in heavily reinforced structures
Common in cast-in-place applications
Advances in Underground Concrete Technology
High-Performance Concrete Mixes
Enhanced strength and durability
Tailored for specific underground environments
Rapid-Setting Formulations
Allows for faster construction cycles
Crucial in time-sensitive mining operations
Self-Compacting Concrete
Reduces the need for vibration in difficult-to-access areas
Sprayed Membranes
Waterproofing layers applied between concrete layers
Enhances long-term durability
Comparison: TSL vs. Traditional Concrete Support
Advantages of TSL
Rapid application and curing
Minimal equipment requirements
Excellent adhesion to irregular surfaces
Lightweight solution
Advantages of Traditional Concrete Support
Well-established technology with extensive performance data
Higher compressive strength
Suitable for major load-bearing applications
Generally lower material costs
Considerations for Choice
Ground Conditions: TSL for minor support, concrete for major support
Application Speed: TSL offers faster application in many scenarios
Load Bearing Requirements: Concrete preferred for high-load situations
Environmental Factors: TSL may offer better corrosion resistance
Project Scale: Concrete more economical for large-scale projects
Future Trends and Research
Eco-friendly Formulations: Development of TSLs and concrete mixes with reduced environmental impact
Hybrid Systems: Combining TSL with traditional support for optimized performance
Smart Materials: Integration of sensors for real-time monitoring of support conditions
Nanotechnology: Enhancing material properties at the molecular level
Automated Application: Robotics and AI for precise and safe application of both TSL and concrete
Conclusion
The world of underground support is evolving, with innovative solutions like Thin Spray-on Liners complementing traditional concrete support methods. While TSLs offer exciting possibilities in terms of speed, flexibility, and specialized applications, conventional concrete support remains indispensable for major load-bearing and large-scale projects. The future of underground support likely lies in the intelligent integration of these technologies, tailored to the specific needs of each project. As research continues and long-term performance data accumulates, we can expect further refinements and novel applications in both TSL and concrete support technologies, ultimately enhancing the safety, efficiency, and sustainability of underground operations.
