In mining and tunneling, structural reinforcement is critical to ensuring safety and operational efficiency. Two widely used support solutions are Thin Spray-On Liners (TSL) and underground concrete support systems. These methods enhance stability in underground spaces, providing essential protection against ground movements, rockfalls, and water ingress. This article explores the role of TSL and concrete support in underground environments, their applications, advantages, and emerging trends in the industry.

 

What Are Thin Spray-On Liners (TSL)?

Thin Spray-On Liners (TSLs) are polymer-based coatings designed to adhere to rock surfaces, forming a thin, protective layer. These liners are used primarily in mining and tunneling to stabilize exposed rock faces immediately after excavation. Unlike traditional concrete layers, TSLs are applied as a very thin layer (ranging from a few millimeters to a centimeter) but provide significant bond strength and resistance to weathering.

Applications of TSL in Mining and Tunneling

1. Temporary Rock Stabilization:
   TSLs are applied immediately after excavation to stabilize rock walls until more permanent support, such as shotcrete or bolts, can be installed.
2. Seepage Control:
   In water-prone areas, TSLs form a protective barrier against water ingress.
3. Scaling Control:
   These liners reduce scaling (the peeling or falling off of rock layers) in underground spaces.
4. Support Enhancement in High-Stress Areas:
   TSLs act as a secondary layer, working alongside other support systems such as rock bolts and shotcrete.

 

Advantages of TSL in Underground Construction

• Rapid Application: TSLs can be sprayed onto surfaces in minutes and cure quickly.
• Lightweight and Thin: They offer support without adding significant weight or volume to the tunnel structure.
• High Adhesion: TSLs bond effectively to various rock types, enhancing stability.
• Cost-Effective: Compared to thicker concrete layers, TSLs are less resource-intensive and easier to apply.
• Improved Safety: Immediate application reduces the risk of rockfalls and worker injuries during excavation.

 

Underground Concrete Support: Overview and Applications

Concrete support systems provide long-term reinforcement for underground structures. In mining and tunneling, concrete is applied either as poured concrete, shotcrete (sprayed concrete), or precast segments. Each method is tailored to meet the specific stability requirements of the site.

Applications of Underground Concrete Support

1. Primary and Secondary Linings in Tunnels:
   Concrete forms the primary lining for initial stabilization and the secondary lining for long-term structural integrity.
2. Reinforcement of Mine Shafts:
   Concrete is used to line and secure vertical mine shafts, preventing collapses during operations.
3. Ground Support in Deep Mines:
   In high-stress environments, such as deep gold or platinum mines in South Africa, concrete supports help manage seismic activity and ground pressure.
4. Water Control and Fireproofing:
   Underground reservoirs and tunnels use concrete linings for waterproofing and fire resistance, ensuring operational safety.

 

Shotcrete vs. Traditional Concrete in Underground Support

While both shotcrete (sprayed concrete) and traditional poured concrete are widely used, shotcrete offers certain advantages in underground applications:

• Speed: Shotcrete can be applied quickly and does not require formwork, which speeds up construction.
• Adaptability: Shotcrete adheres to irregular surfaces, making it ideal for tunnels and mine shafts.
• Reduced Labor: Mechanized spraying minimizes manual labor, reducing project costs and time.

 

How TSL and Concrete Support Work Together

In many underground projects, TSL and concrete supports are used in combination to ensure optimal stability:

• TSL as a Temporary Measure: TSLs stabilize rock faces during the early stages of excavation, providing time for workers to install more permanent support systems.
• Concrete as Permanent Support: Once TSLs are in place, shotcrete or poured concrete is applied to reinforce the tunnel or shaft over the long term.
• Layered Defense System: TSLs prevent small-scale rockfalls and surface peeling, while concrete provides load-bearing capacity to withstand ground pressures.

 

Advantages of Combining TSL and Concrete Support

1. Enhanced Safety: TSL provides immediate stabilization, reducing risks during the excavation phase.
2. Reduced Downtime: Using TSL allows workers to proceed with excavation without waiting for concrete layers to cure.
3. Cost-Effectiveness: The combination of TSL and shotcrete reduces material waste and optimizes labor resources.
4. Seamless Integration: Both systems complement each other, ensuring reliable support even in high-stress environments.

 

Challenges in Underground Concrete Support and TSL Application

• Environmental Conditions: High humidity or water ingress can affect the performance of TSL and concrete.
• Rebound Waste in Shotcrete: Some material may not adhere to surfaces, requiring careful waste management.
• Skilled Workforce Required: Both TSL and concrete application require trained operators for optimal performance.
• Seismic Activity: Underground structures in seismically active zones may need additional reinforcement beyond TSL and shotcrete.

 

Innovations in TSL and Concrete Support Systems

The industry is seeing significant advancements in both TSL and concrete technologies to enhance safety and efficiency:

• Fiber-Reinforced Shotcrete (FRS): Adding fibers to shotcrete improves strength and crack resistance.
• Robotic Application: Automated spraying systems improve the precision and consistency of TSL and shotcrete applications.
• Eco-Friendly Materials: New formulations reduce the carbon footprint of concrete, contributing to sustainable construction practices.
• Smart Monitoring Systems: Sensors embedded in concrete can provide real-time data on structural integrity, helping identify weak spots early.

 

Case Studies: South Africa’s Use of TSL and Concrete Support

1. Deep-Level Mining in the Witwatersrand Basin:
   South Africa’s deep-level gold mines rely heavily on shotcrete and TSL solutions to manage rock bursts and ground pressure. These solutions ensure the safety of workers in some of the deepest mines in the world.
2. Gautrain Project:
   The Gautrain tunnel network utilized a combination of shortcrete linings and TSL to stabilize tunnel walls during excavation, ensuring safe and efficient construction under challenging conditions.
3. Platinum Mines in the Bushveld Complex:
   In high-stress mining environments, TSL and fiber-reinforced shotcrete provide essential support, enabling deeper excavation without compromising safety.

 

Conclusion: Building Safer Underground Spaces

TSL and underground concrete support systems play a vital role in ensuring the safety and longevity of underground structures. While TSL offers immediate stabilization during excavation, shotcrete and other concrete solutions provide long-term reinforcement. Together, these systems create a layered defense against rock falls, ground movements, and environmental challenges.

In South Africa’s mining and infrastructure sectors, the combination of TSL and concrete support has proven to be a reliable and efficient method for managing underground risks. As technology continues to evolve, robotic application, fiber reinforcement, and smart monitoring systems will further enhance the safety and performance of these solutions, ensuring that South Africa remains at the forefront of underground construction innovation.