Tunnel engineering, as a crucial part of transportation construction, has a decisive impact on the success of the project. Taking the Qinling Zhongnanshan Highway Tunnel—the longest twin-bore, one-way highway tunnel in the world—as an example, this tunnel spans 18.02 kilometers and fully showcases advanced construction techniques and strict construction principles.
When discussing tunnel construction, the Qinling Zhongnanshan Highway Tunnel, the world's longest twin-bore, one-way highway tunnel, often comes to mind. This tunnel starts in Qingcha, Chang'an District, Xi'an City, and ends in Yingpan Town, Zhashui County, Shangluo City, spanning 18.02 kilometers. With a design speed of 80 kilometers per hour, it takes only 15 minutes to traverse the Qinling Mountains, which form the natural dividing line between northern and southern China. Notably, this world record was entirely designed and constructed by China, incorporating highly human-centric design concepts. This article will detail the construction techniques and principles of tunnel construction.
Principles of Tunnel Construction
Before commencing tunnel construction, a thorough investigation of the weak surrounding rock on-site is essential, with a deep understanding of the design intentions. Based on different geological conditions, practical construction plans are developed. During construction, the following principles must be strictly adhered to:
1. Attention to Geological Conditions:** Accurately understand geological conditions, particularly the characteristics of weak surrounding rock areas.
2. Proactive Control： Maintain proactive control during construction to prevent potential problems.
3. Strict Grouting： Perform grouting reinforcement of the geology to ensure stability.
4. Short Advances： Conduct construction in segments to ensure the quality of each section.
5. Strong Support： Implement effective support measures to ensure the stability of the tunnel structure.
6. Frequent Measurements： Regularly measure and monitor various tunnel parameters to promptly detect and resolve issues.
7. Early Closure： Timely closure of the excavation face to reduce the risk of collapses.
Tunnel Construction Techniques
The techniques used in tunnel construction vary depending on the classification of the surrounding rock:
- Full-face Method： Suitable for Class III rock sections, involving one-time full-face excavation to ensure construction efficiency.
- Step Method Excavation： Suitable for Class IV and V rock sections, involving step-by-step excavation and gradual support to ensure safety.
For support, initial support measures include rock bolts, steel meshes, and shotcrete, with advanced construction of the invert to ensure tunnel stability. The arch walls are constructed in a single pass to ensure structural integrity and durability.
In sections with active fault zones or requiring seismic fortification, full-circle steel arch frames and double-layer φ42 small guide pipes for the arch are used for advanced support to enhance seismic performance. Lining inside the tunnel employs lining trolleys to ensure construction precision and efficiency.
Technological Applications in Construction
During construction, advanced geological prediction and forecasting are crucial. Techniques such as deep blast hole detection and infrared detection confirm the geological conditions ahead and detect differences between design and actual geology. In critical geological hazard sections, advanced horizontal drilling techniques ensure accurate geological understanding. Meticulous measurements are conducted throughout the construction process, analyzing settlement observation data to adjust construction plans in a timely manner.
Tunnel construction is a complex and precise engineering task requiring scientific planning and strict management. By adhering to scientific construction principles and adopting advanced construction techniques, the smooth progress of tunnel construction and the long-term safe operation of tunnels can be ensured. The successful construction of the Qinling Zhongnanshan Highway Tunnel is a powerful testament to this approach.