Advancing Tunnel Sustainability with Fibre-Reinforced Shotcrete

Recent advancements in sprayed fibre-reinforced concrete (SFRC) technology are reshaping the way tunnels are designed and constructed. With nearly 70% of a tunnel’s embodied carbon coming from concrete linings, a transition from traditional cast-in-place (CIP) methods to Permanent Sprayed Concrete Linings (PSCL) offers a significant step forward in reducing environmental impact.

By adopting PSCL which is also known as the Single Shell Method, tunnel projects can reduce material-related CO₂ emissions by up to 75%. This approach eliminates the need for a separate permanent CIP layer and replaces conventional steel reinforcement with high-performance steel fibres, reducing concrete volume, reinforcing steel, and overall construction time. The result is a lighter, more sustainable structure that maintains high mechanical strength and long-term durability.

To ensure the structural reliability of fibre-reinforced sprayed concrete, testing standards have evolved alongside the technology. The EN 14488-3 Method B now provides an improved approach to determining residual strength through three-point bending tests on sprayed panels rather than cut beams.

Studies conducted by the Universitat Politècnica de Catalunya (UPC) demonstrated that sprayed panels reinforced with 40 kg/m³ of Dramix 4D 65/35BG steel fibres achieved strength class 3c with lower variability compared to traditional cast beams. Further research presented by CETU highlighted that strength class 4c can be achieved using advanced high-tensile fibres. This development confirms that PSCL can meet both service and ultimate limit states required for long-term tunnel support.

Modern SFRC systems now integrate digital quality assurance tools such as the eyeD® Inspector, an inductive device that measures steel fibre content and orientation in situ. This allows for more accurate verification of fibre distribution before large-scale applications.

Steel remains the most recycled material worldwide, and the use of remelted fibres enhances sustainability while avoiding microplastic pollution associated with polymer fibres. With governments increasingly banning plastic-based reinforcement, the use of steel fibre reinforced shotcrete aligns with new environmental standards and circular economy principles.