What are the characteristics of modern tunnel construction?
The characteristics of modern tunnel construction and development are closely related to scientific and technological progress, social and economic development and sustainable development concepts:
a. The progress of human science and technology, especially the rapid development of computer technology and information technology, enables the force of the tunnel excavation process to be accurately controlled through numerical simulation and monitoring and measurement information feedback, and realizes the “dynamic design and construction”;
b. The mechanical equipment for tunneling is constantly improved and intelligent, which can protect the integrity of the surrounding rock and the safety of the construction process to the maximum extent;
c. The concepts of energy saving, emission reduction, ecological protection and sustainable development are gaining more and more popularity;
d. The people-oriented construction concept is continuously deepened.
According to the above concept, combined with the characteristics of modern tunnel construction and operation, it can be summarized into the following aspects:
1) The tunnel is repaired longer
With the improvement of road grade standards and the continuous improvement of tunnel design theory and construction technology, the construction length of highway tunnels has grown from 2 ~ 3km in the 19th century to tens of kilometers now. In the 20th century, the Guanyue tunnel in Japan was 11.06km long, the Mont Blanc tunnel in Italy was 11.6km, the Orland tunnel in Norway was 24.5km, and the Xinguanjiao tunnel in China was 32.6 in this century. km, the new Gotthard tunnel in Switzerland is 57.0km long. In addition, Qinling Zhongnanshan Tunnel, the longest road tunnel in China with a total length of 18.02km, has been constructed. The successful construction of these long highway tunnels, in addition to the increased requirements of highway grade standards, new construction techniques, modern ventilation monitoring technology, and many successful experiences play a decisive role.
2) More and more curved tunnels
Driven by the new tunnel design theory and construction technology, especially after summarizing the practical experience of highway tunnel operation and management, the route selection of modern kilometers of tunnels has completely broken the previous rules of straightness and no bending. Curved tunnels are gradually increasing. It is more common in foreign countries. For example, the Balassky double-track tunnel in Austria has designed a curved tunnel with a length of 1.2km in combination with the terrain and environmental conditions. The main reasons for the increasing number of curved tunnels are:
a. Avoid bad geological areas and improve the safety of the tunnel structure;
b. Limit the driving speed to fully ensure driving safety;
c. It can effectively control the glare caused by accelerating out of the hole, which is very helpful to avoid traffic accidents.
3) The tunnel span is getting bigger and bigger
From the perspective of geotechnical mechanics, the span of the tunnel is an important indicator that can be used to measure the stability of the tunnel project and the difficulty of construction. Generally speaking, the larger the span, the more unfavorable the stability of the surrounding rock of the cave. In addition, the larger the span, the greater the impact of adverse geological conditions (such as faults, etc.), which will cause difficulties in tunnel construction. Therefore, the construction and operation of large-span tunnel underground engineering marks the new progress and maturity of investigation, design and construction technology.
4) Longitudinal ventilation is dominant
In the 20th century, most of the nearly 400 highway tunnels with a length of more than 3km built abroad were fully horizontal or semi-horizontal ventilation, represented by Switzerland, Austria and Italy.
In recent years, with the practice of longitudinal ventilation in long highway tunnels, the ventilation methods of highway tunnels are basically divided into two groups: horizontal ventilation or semi-horizontal ventilation represented by Europe and vertical represented by Asia and Japan Type ventilation. With the increase of vehicle emission limit standards, the factors that control the ventilation volume of highway tunnels have gradually transitioned from CO to smoke concentration, and the double-hole scheme has gradually replaced the single-hole scheme. Therefore, segmented vertical ventilation has become dominant. Japan believes that the sectioned longitudinal ventilation method with electrostatic precipitator can be adapted to any traffic and highway tunnel of any length. European countries have also gradually changed their traditional ideas. In many newly built or extended double-track long road tunnels, the horizontal ventilation method in the past has been used to replace the horizontal ventilation method in the past. Several long and large highway tunnels constructed in China basically adopt longitudinal ventilation or section longitudinal ventilation.
5) Double holes replace single holes
Single-hole two-way traffic cannot fully utilize vehicle traffic wind, and requires increased installed capacity of ventilation equipment, especially the accident rate of single-hole two-way traffic is much higher than that of double-hole one-way traffic. Cave two-way traffic tunnel. According to incomplete statistics, foreign countries are changing more than 100 single-hole two-way traffic tunnels built in the early days into double-hole one-way traffic tunnels, which is very helpful for reducing the difficulty of ventilation, saving energy, and reducing traffic accidents.
In addition, the double-hole traffic can greatly increase the traffic volume and meet the requirements of disaster prevention, disaster relief and combat readiness. The Balaski tunnel and the Tauern tunnel in Austria are typical examples.
The highway tunnels constructed in China are all double-hole one-way traffic tunnels. However, the secondary roads and the road tunnels below the second level are basically single-hole two-way traffic tunnels. With the increase of traffic volume, the single-hole two-way traffic tunnels of some secondary highways have gradually changed to double-hole one-way traffic tunnels.
6) Diverse tunnel functions
The main function of highway tunnels is for car traffic, that is, traffic function. However, the long road tunnels built by humans, especially the extra-long road tunnels, the tunnels that are difficult to construct and the high-cost tunnels, will arouse the people’s attention and curiosity. Therefore, tourism has become a long road tunnel Another obvious feature, prominent examples are the English Channel Tunnel, Tokyo Bay Tunnel, Hong Kong Bay Tunnel and Shanghai Yanan East Road Tunnel.
7) Underground interchange is becoming a reality
At present, the domestic underground engineering construction is developing rapidly, but its function is partial, and the city should take the road of deep stratum, multi-function and three-dimensional development in the future to truly achieve the sustainable development of the city. In this regard, some cities in Europe and the United States have come to the forefront. Underground expressways have been built in Boston, USA and Tokyo, Japan. Highway interchange interchanges have large spans, complex structures, and difficulty in close-up construction. The operation techniques such as ventilation and disaster prevention are more difficult, which poses challenges to tunnel design theory and construction techniques. At present, China’s highway interchange is also starting. For example, the first large-scale underground underground interchange in China-Xiamen Wanshishan Underground Interchange Tunnel is an underground interchange structure that has both plane bifurcations and upper and lower intersections, and its structural characteristics are manifested. It is the largest span structure section width 25.8m; the double arch section is asymmetrical structure, and the small clear interval section contains 1.42 m rock.
In summary, the tunnel project has become an important part of national construction and people ’s life and production. It is a manifestation of space expansion and resource intensiveness. It is also a collection of geology, geotechnical, structural, computational mechanics, machinery, electromechanical, information control and disasters. Comprehensive technology of prevention and emergency response in multiple disciplines and fields. Although tunnel construction and technology in China have achieved great achievements in recent years, there are still many problems that need to be further studied and resolved. Due to the irreversible and difficult-to-change characteristics of the tunnel, it is difficult to change once it is completed. Therefore, the planning, design, and construction of tunnel construction must be scientific, rational, and high-quality.