MINING
In general, shotcrete is used in underground mining for ground control with a design life for supporting the ground ranging from a few weeks to 50+ years.
Common approaches for strength design of shotcrete linings in mining applications are analytical (comparison of potential load actions and load resistance) and empirical (based largely past experiences).
Shotcrete has become an indispensable component in the mining industry, particularly in underground operations. Its introduction to Australian mines dates back to 1994, marking a significant shift in ground support methodologies.
Evolution of Shotcrete in Mining
- Early Adoption: Initially, shotcrete was applied over installed mesh and bolts in areas with inadequate ground support. Over time, Fiber Reinforced Shotcrete (FRS) progressively replaced mesh as the preferred method of ground support in underground mines.
- Safety and Efficiency: The adoption of shotcrete greatly enhanced safety by reducing personnel exposure to unsupported ground and improved the overall level of ground support achieved.
- Seismic Resilience: In seismically active areas, shotcrete is reinforced with mesh over its layer to provide additional support due to the greater ductility of un-encased mesh.
- Widespread Use: Today, virtually all underground mines in Australia employ shotcrete for ground support, indicating its effectiveness and reliability.
Design Considerations in Mining
- Tailored Approach: Mine design for shotcrete support differs from tunnel design due to varying excavation orientations, depths, and stress conditions. This requires the assessment of geotechnical consultants or engineers.
- Substrate Preparation: The performance of shotcrete can be significantly affected by the quality of substrate preparation, emphasizing the importance of surface cleanliness, water flow, and joint treatment.
Specialized Applications and Techniques
- Vertical Applications: Dry shotcrete is typically used in vertical applications over 50 meters deep, influenced by the weight of the material and delivery challenges.
- Mechanized Methods: Mechanized shotcrete applications, such as remote shaft lining and tunnel boring machine integration, have increased in popularity due to stringent safety standards and the need to minimize personnel exposure to hazardous areas.
Challenges in Curing
- Curing Difficulties: In the underground mining environment, curing shotcrete is challenging due to factors like hot rock surfaces and high velocity ventilation flow. This often leads to shrinkage cracking.
- Innovative Solutions: Water spray curing is sometimes used, and internal curing agents have been developed to improve the mechanical properties of shotcrete, enhancing its performance by at least 20% for a minimal cost increase.
The integration of shotcrete in mining has revolutionized underground operations, offering enhanced safety, efficiency, and adaptability to varying geological conditions. Its continuous evolution and adaptation underscore its critical role in modern mining practices in Australia.
Also see: Concrete Institute of Australia - Shotcreting in Australia
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