What are the current tunnel construction methods in China

At present, the construction of railway and highway mountain tunnels in China mainly adopts the New Austrian Tunneling Method, with anchor spray support as the main means and secondary lining as a reserve, closely following the construction of the excavation face to the maximum extent, prioritizing the safety of the excavation face construction, and controlling the deformation of the surrounding rock before support to a limited extent, fully exerting the self stability of the surrounding rock, and preventing the surrounding rock from entering a loose state. Anchor rods play a key role in this process. A large amount of engineering experience and experimental evidence have shown that prestressed anchor rods have better support effects than non prestressed anchor rods due to their fast and active action characteristics. Traditional non prestressed anchor rods are mainly passively stressed and require longer hardening or anchoring time, which is not conducive to the rapid construction of tunnels and the reinforcement and stability of surrounding rocks, affecting construction safety. In addition, with the rapid development of China's railways and highways, the construction areas continue to expand towards the western plateau and southern mountainous areas. The geological conditions encountered in engineering construction are becoming increasingly complex and varied, and the design theory is shifting from passive support to active support. Tunnel engineering has increasingly strict requirements for anchor rod support, especially in terms of timeliness.