High strength steel fibers are mainly used in tunnel construction for shotcrete and lining structures to enhance the mechanical properties and durability of materials. Steel fibers are usually made of steel with a tensile strength of not less than 380MPa, with a diameter range of 0.3~0.5mm and a length between 20~25mm. The dosage generally accounts for 1%~3% of the mass of the concrete mixture. This material is mixed with ordinary concrete to form steel fiber reinforced concrete (SFRC), which significantly improves crack resistance, impact resistance, and fatigue resistance.

In terms of mechanical properties, steel fiber reinforced concrete can effectively suppress crack propagation, increasing tensile strength by 40% to 80% and flexural strength by 60% to 120%. For example, in the single-layer lining support of the inclined shaft of Motianling Tunnel, the application of steel fiber reinforced concrete enhances structural toughness and reduces rebound losses during spraying operations. At the same time, the compressive strength of concrete mixed with 1.5% steel fibers can reach 54.6MPa, which is about 20% higher than ordinary concrete, and the flexural strength increases from 6.4MPa to 9.2MPa.

In terms of construction efficiency and cost optimization, steel fiber reinforced concrete can replace traditional steel mesh support, simplify the process, and reduce material usage. The Hong Kong City Gate Road Tunnel adopts wet mixed steel fiber shotcrete construction, combined with automatic spraying by mechanical arms, which improves construction efficiency by more than 50%. The tunnel of Qixi Hydropower Station in Zhejiang Province is supported by full section steel fiber, reducing the lining thickness from 50cm to 6cm and saving material costs. In addition, the application of synthetic fibers such as polypropylene fibers in shotcrete can also reduce the rebound rate by 35% and improve material utilization.

In terms of durability and structural safety, the crack width of steel fiber reinforced concrete can be controlled within 0.08mm, which is better than the 0.18mm of ordinary concrete, and the anti-seepage pressure reaches 1.6MPa, significantly higher than the 0.9MPa of ordinary concrete. In mountainous highway tunnels, the addition of steel fibers with a volume fraction of 1.2% increased the flexural strength by 40%, reduced the number of cracks by about 75%, and enhanced long-term stability. After using steel fiber reinforced concrete for shield tunnel segments in urban subway tunnels, the impact resistance and impermeability have been improved, the transportation and installation damage rate has been reduced by 60%, and the deformation has been reduced by 30%.

Actual engineering cases have shown that steel fiber reinforced concrete performs outstandingly in complex geological conditions and high demand environments. For example, the cross sea tunnel project uses steel fiber reinforced concrete secondary lining, which extends the crack resistance period of the structure from 3 years to 15 years; The high-altitude tunnel project solved the problem of low-temperature shrinkage cracking by optimizing the fiber content, and increased construction efficiency by 40%. These applications have validated the value of high-strength steel fibers in enhancing the safety, durability, and economy of tunnel engineering.