How to choose tunnel construction method?
Tunnel construction is a highly complex and intricate process, requiring careful consideration of multiple key factors. These factors range from natural and technical aspects—such as geological conditions, tunnel length, cross-sectional dimensions, and construction environment—to broader concerns, including economic feasibility and safety. In practical applications, various tunnel construction methods have been widely adopted, each with its distinct characteristics and suitable scenarios. This article provides a detailed analysis of commonly used tunnel construction methods, outlining their advantages and limitations.
1. Traditional Drill and Blast Method
The drill and blast method is a conventional tunneling technique that involves drilling precise holes, loading explosives, and detonating them to achieve either full-section or partial excavation.
This method is particularly effective in hard rock formations, where it leverages the natural conditions to directly form a solid tunnel structure. It plays a crucial role in the construction of mountain tunnels, subway tunnels, and certain undersea tunnels due to its adaptability and efficiency.
However, in complex geological conditions—such as undersea tunnels—the drill and blast method faces challenges, including large excavation volumes and structural limitations posed by geological formations.
- Advantages: Well-suited for hard rock formations; enables direct utilization of natural conditions to form a robust tunnel structure.
- Disadvantages: In complex geological conditions (e.g., undersea tunnels), it requires extensive excavation and is constrained by geological structures.
2. Modern and Efficient Shield Tunneling Method (TBM)
The shield method, which employs a Tunnel Boring Machine (TBM), is a modern, highly efficient, and safer tunneling technique compared to traditional excavation methods.
This method utilizes a large shield machine that advances through the ground, cutting and removing soil while simultaneously assembling pre-fabricated tunnel lining segments. The shield method ensures safe construction with minimal disturbance to surrounding strata, precise control of rock perimeters, and negligible over-excavation.
It is particularly suitable for urban subway tunnels, cross-river tunnels, cross-sea tunnels, and tunnels in soft geological formations. However, the high acquisition cost of TBM equipment and the complex production process of prefabricated lining segments pose limitations to its application in certain projects.
- Advantages: Ensures safe construction with minimal geological disturbance; precise control over excavation; ideal for tunnels in soft ground conditions, such as urban subway and underwater tunnels.
- Disadvantages: High cost of TBM acquisition and the complexity of prefabricating tunnel lining segments.
3. Specialized Immersed Tube Method
The immersed tube method is a unique construction technique specifically designed for large-scale underwater tunneling projects. It involves prefabricating tunnel sections on land, transporting them to the designated location using flotation technology, and then submerging and docking them on the seabed.
Although the construction process is relatively complex and requires meticulous coordination, the immersed tube method is well-suited to the extreme conditions of undersea environments. A notable example of its successful application is the Hong Kong-Zhuhai-Macao Bridge (HZMB) undersea tunnel, which demonstrated the reliability and effectiveness of this technique in large-scale underwater projects.
- Advantages: Specifically adapted for undersea environments, ensuring tunnel stability and safety under extreme conditions.
- Disadvantages: The construction process is highly complex and requires precise planning and execution.
4. Highly Efficient and Precise Roadheader Method
The roadheader method is recognized for its efficient and precise excavation capabilities. It involves the use of a roadheader machine, which directly excavates the tunnel by cutting through the ground, ensuring rapid tunnel formation.
This method offers several advantages, including minimal geological disturbance, precise section control, and elimination of over-excavation. It also enhances construction speed and reduces the required workforce. However, the high cost of roadheader equipment limits its widespread application in certain projects.
- Advantages: Provides highly efficient and precise excavation with minimal disturbance; enhances construction speed and reduces labor requirements.
- Disadvantages: High equipment costs restrict its use in some projects.
5. Simple and Cost-Effective Cut-and-Cover Method
The cut-and-cover method is a relatively simple and economical tunneling approach compared to other methods. It involves excavating a trench, constructing the tunnel structure within it, and then backfilling the excavation.
Despite its simplicity and cost advantages, this method requires significant surface space and has a substantial impact on traffic and the environment. Consequently, it is primarily used for shallow tunnels or urban railway tunnels where surface disruption is manageable.
- Advantages: Straightforward construction process with lower costs.
- Disadvantages: Occupies a large surface area and disrupts traffic and the environment; mainly applicable to shallow tunnels or urban railway tunnels.
6. Concealed Excavation for Complex Geological Conditions
The concealed excavation method involves tunnel excavation and structural support without disturbing the ground surface. While it minimizes surface impact, this technique requires highly advanced construction expertise and poses significant technical challenges.
As a result, it is predominantly used in mountain railway tunnels and urban subway tunnels under challenging geological conditions. The successful application of this method showcases the engineering ingenuity required to overcome complex geological constraints.
- Advantages: Minimal impact on surface structures and environment.
- Disadvantages: Complex and technically demanding; mainly used in mountain railway tunnels and subway tunnels under difficult geological conditions.
7. Flexible and Versatile Benching Method
The benching method is a flexible and adaptable tunneling technique that divides the tunnel section into multiple parts for sequential excavation. Various excavation techniques, such as the step method, CD method, CRD method, and double sidewall guide pit method, can be employed based on specific geological conditions and project requirements.
This method is particularly effective in complex geological conditions, such as weak rock formations and large-span tunnels. Its flexibility and adaptability make it a valuable choice for tunneling projects that demand customized excavation strategies.
- Advantages: Highly adaptable to diverse geological conditions, including weak rock formations and large-span tunnels; allows for the selection of optimal excavation techniques.
- Disadvantages: Requires careful selection of excavation techniques based on site-specific geological and construction conditions.
Conclusion：
There are various tunneling methods available, each with its unique applications, advantages, and limitations. Selecting the appropriate construction method requires a comprehensive assessment of factors, including geological conditions, construction environment, economic feasibility, and safety considerations. By making well-informed decisions, engineers can ensure the smooth execution and high-quality completion of tunnel projects.
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