Research Summary of Shotcrete Technology in Tunnel Engineering

China's tunnel engineering is rapidly advancing towards long-distance, large cross-section, and deep burial. High temperature and high stress geological conditions not only easily induce thermal and moisture diseases, but also exacerbate surrounding rock deformation, ultimately leading to the failure of support structures. This has put forward higher requirements for the performance and construction technology of shotcrete. This article systematically reviews the research progress of shotcrete at home and abroad, with a focus on analyzing the influence of accelerators, mineral admixtures, and fiber-reinforced materials on the mechanical properties, microstructure, and durability of shotcrete. The construction process and quality control methods are systematically summarized. The research results indicate that although alkaline accelerators can improve early strength, they will reduce durability, and non alkaline accelerators have gradually become the mainstream choice; Mineral admixtures can effectively improve mechanical properties and durability, while adding fibers can transform the failure mode from brittle fracture to ductile failure. The quality of shotcrete construction is closely related to material preparation, transportation, and spraying operations, among which the spraying operation stage is significantly affected by factors such as the angle between the nozzle and the rock surface, distance, spraying pressure, layer thickness, and time interval. In summary, in the future, the focus should be on developing low-cost, high durability, and environmentally friendly shotcrete, building a construction process system that integrates less manpower, automation, and information technology, and promoting the transformation and upgrading of tunnel construction towards green and intelligent directions.