Support in tunneling is critical to maintaining tunnel stability and preventing collapses, especially in weak or unstable ground conditions. There are several methods of support used in tunneling, and the selection depends on factors such as the type of soil or rock, the depth of the tunnel, groundwater conditions, and the size and shape of the tunnel. Here are the main methods:

　　1. Temporary Supports

　　Used during the construction process to ensure immediate stability.

　　- Steel Ribs and Timbering: Steel ribs (arched sections) are often used in combination with timber to temporarily support the tunnel.

　　- Tunnel Lining: A preliminary lining (often shotcrete) can be sprayed on the exposed rock or soil to provide temporary support until permanent lining is applied.

　　- Shields: Used in soft ground conditions, shields are large cylindrical devices that provide temporary support to the tunnel face and surrounding area while the excavation progresses.

　　2. Permanent Supports

　　These are designed to last the lifespan of the tunnel and provide long-term stability.

　　- Concrete Linings: This is one of the most common methods. Reinforced concrete is poured in situ (on-site) or prefabricated concrete segments are assembled to form a permanent support structure.

　　- Shotcrete (Sprayed Concrete): Shotcrete is concrete or mortar that is sprayed onto the tunnel surface using high-pressure hoses. It can contain steel or synthetic fibers for additional strength.

　　- Rock Bolts and Cable Bolts: Rock bolts are inserted into drilled holes to reinforce rock masses. These bolts stabilize the surrounding rock and are often used with shotcrete or wire mesh for added support.

　　- Grouting: Injection of cement or chemical grout into the surrounding ground can improve the strength and reduce permeability of the soil or rock mass. Grouting is used in both soft soils and fractured rock to stabilize and reduce water inflow.

　　- Steel or Cast Iron Linings: Often used in segments, these linings are placed in tunnels under high pressure or in soft soil to prevent collapse. They are durable and provide robust support.

　　3. Ground Improvement Techniques

　　Used to enhance the stability of the ground before or during tunnel excavation.

　　- Ground Freezing: Liquid nitrogen or brine is circulated through pipes embedded in the ground to freeze water within the soil, forming a temporary solid barrier.

　　- Jet Grouting: A high-pressure jet of cement slurry is injected into the ground to create columns of solidified material that improve the strength and reduce water inflow.

　　- Soil Nailing: This method reinforces the surrounding soil by inserting steel bars or nails into pre-drilled holes in the ground, helping to stabilize the tunnel face.

　　4. Tunnel Boring Machine (TBM) Support

　　Modern tunneling uses a TBM, which combines excavation and support systems.

　　- Segmental Linings: Precast concrete or steel segments are placed directly behind the TBM to support the tunnel walls as the machine advances. This is often used in soft ground or waterlogged conditions.

　　5. Sequential Excavation Method (SEM) / New Austrian Tunneling Method (NATM)

　　This is a widely used method that involves incremental excavation and support.

　　- Controlled Excavation: The tunnel is excavated in sections, with support applied immediately after each section is dug. This minimizes deformation and collapse risks.

　　- Shotcrete and Rock Bolts: These are applied during the excavation stages to stabilize the tunnel, and instrumentation is often used to monitor movement within the tunnel.

　　6. Other Techniques

　　- Lattice Girders: Steel lattice girders are placed in the tunnel roof, with shotcrete sprayed over them for support. These are often used in combination with other methods.

　　- Spiling: Steel rods or plates are inserted ahead of the tunnel face to support the ground as excavation proceeds.

　　Each method can be used alone or in combination, depending on the tunneling conditions and project requirements.