Tunnel support methods
Tunnel support methods vary depending on factors like the type of rock or soil, the size of the tunnel, and the specific requirements of the project. Here are some common tunnel support methods:
As we discussed earlier, rock bolts are commonly used to reinforce rock in tunnels. They are installed by drilling holes into the rock and inserting long steel bolts, which are then tightened to provide support.
Shotcrete: Shotcrete, also known as sprayed concrete, is a method where concrete is sprayed onto the tunnel walls and roof using a hose. It provides immediate support and helps to stabilize the rock or soil.
Steel Rib Support: Steel ribs, or lattice girders, are often used to support tunnel walls and roofs. They are installed either by hand or using machinery and provide structural support to the tunnel lining.
Steel Sets: Steel sets consist of steel beams or frames that are installed to support the tunnel walls and roof. They are often used in combination with other support methods, such as shotcrete or rock bolting.
Mesh and Wire Mesh: Mesh and wire mesh are used to reinforce shotcrete and provide additional support to the tunnel lining. They help to distribute loads and prevent spalling or cracking of the concrete.
Grouting: Grouting involves injecting a cementitious or chemical grout into the surrounding rock or soil to improve its strength and stability. It can be used to fill voids, consolidate fractured rock, or improve the bonding of rock bolts.
Concrete Lining: In some cases, tunnels are lined with a layer of reinforced concrete to provide additional support and protect against water infiltration.
These are just a few examples of tunnel support methods, and often, a combination of these techniques is used to ensure the stability and safety of the tunnel structure. The choice of method depends on factors such as geological conditions, budget, and the desired lifespan of the tunnel.
What is a rock bolt used for in a tunnel?
Rock bolts are extensively used in tunnel construction for stabilization and reinforcement purposes. They serve several key functions:
Stabilization of Loose Rock: In tunnels where the surrounding rock is fractured, fragmented, or otherwise unstable, rock bolts are employed to secure the rock mass. By anchoring into the stable rock layers beyond the unstable zone, rock bolts prevent collapses, rockfalls, and other hazards.
Support for Tunnel Roofs and Walls: Rock bolts provide structural support to tunnel roofs and walls, enhancing their stability and preventing deformation or collapse. This support is crucial for maintaining the integrity of the tunnel structure and ensuring the safety of workers and equipment inside.
Reduction of Ground Movement: In tunnels excavated through rock masses prone to deformation or squeezing, such as in squeezing ground conditions, rock bolts help minimize ground movement by reinforcing the surrounding rock. This reduces the risk of tunnel closure or damage during excavation and operation.
Distribution of Load: Rock bolts distribute the load applied to the tunnel lining more uniformly across the rock mass. This helps mitigate stress concentrations and prevents localized failures, improving the overall stability and longevity of the tunnel.
Facilitation of Excavation: By stabilizing the surrounding rock, rock bolts facilitate the excavation process by providing a safer working environment for tunneling crews and equipment. This enables more efficient and timely progress in tunnel construction projects.
Overall, rock bolts play a crucial role in ensuring the stability, safety, and longevity of tunnels by reinforcing and stabilizing the surrounding rock mass. They are a fundamental component of tunnel support systems, particularly in challenging geological conditions.
What is the purpose of welded wire mesh in tunnel support？
In tunnel support, welded wire mesh serves several critical purposes:
Reinforcement of Shotcrete: Shotcrete, a spray-applied concrete, is commonly used for tunnel linings. Welded wire mesh is often installed within the shotcrete to reinforce it, enhancing its tensile strength and resistance to cracking. This reinforcement helps to maintain the integrity of the tunnel lining and provides additional support against ground movement and pressure.
Surface Stabilization: Welded wire mesh is used to stabilize the exposed rock or soil surfaces within the tunnel. By covering the walls and roof with mesh, it helps to prevent loose debris and rock fragments from falling, reducing the risk of rockfalls and ensuring the safety of workers and equipment inside the tunnel.
Erosion Control: In tunnels constructed through unstable or erodible geological formations, welded wire mesh can be employed to control erosion and stabilize the surrounding terrain. The mesh acts as a barrier to prevent soil and rock from sloughing off and helps to maintain the structural integrity of the tunnel and its surroundings.
Support for Rock Bolts and Anchors: Rock bolts and other ground support systems are commonly used in tunnels to reinforce the surrounding rock mass. Welded wire mesh provides a stable surface for the installation of these support elements, ensuring proper anchorage and distribution of forces within the rock mass.
Crack Control and Structural Integrity: By providing uniform support and reinforcement to the tunnel lining, welded wire mesh helps to control cracking and maintain the structural integrity of the tunnel. This is particularly important in tunnels subjected to dynamic loading, ground movement, or seismic activity, where maintaining a stable and durable structure is essential for safety.
Overall, welded wire mesh plays a crucial role in tunnel support by enhancing the stability, durability, and safety of the tunnel structure. It provides reinforcement, surface stabilization, and erosion control, contributing to the long-term performance of the tunnel in various geological and environmental conditions.
