NATM and traditional law

The primary support of NATM mainly adopts bolt-shotcrete support. These measures aim to make full use of the self-supporting capacity of rock mass and reduce the disturbance to surrounding rock, so as to achieve the purpose of safe and efficient construction. The use of steel frame or grid steel frame is mainly aimed at traditional tunnel construction methods such as mining method, which is used to strengthen the stability of initial support and prevent rock caving and mudding.

NATM usually does not carry out secondary lining after the initial support, because the secondary lining will increase the construction difficulty and cost, and the initial support of NATM is enough to ensure the safety and stability of the tunnel. However, in some special circumstances, such as when the tunnel crosses the earthquake zone or has strict environmental requirements, secondary lining reinforcement may be needed.

For mining construction, steel frame is often used for initial support to strengthen the stability of initial support and prevent rock caving and mud. At the same time, this mining method usually carries out secondary lining reinforcement after the initial support to further improve the safety and stability of the tunnel. Compared with NATM, the mining method pays more attention to the strong support of rock mass, rather than making full use of the self-supporting capacity of rock mass.