Present situation and development prospect of highway bridges and tunnels in China

China is a mountainous country, and about 75% of its territory is mountains, rivers and vast oceans. In recent 10 years, an average of 350km of highway tunnels were built every year (see figure 1), and 28 underwater highway tunnels were built, which played an increasingly important role in traffic infrastructure construction. At the same time, in urban construction, urban road tunnels aiming at saving land and protecting the environment are also in the ascendant. Generally speaking, highway tunnels go from heavy hills to deep mountains, from land to underwater, and from mountains to cities. In the face of increasingly frequent disasters such as earthquakes, fires and rainstorms, complex geological conditions such as high ground stress, active faults, cold, high altitude and abundant water, increasingly enhanced construction concepts such as environmental protection and energy conservation, and the actual needs of the construction of important strategic passages such as crossing rivers, seas and plateaus in China, there are still outstanding technical bottlenecks to be solved urgently.

Second, the review of the development of highway tunnels in China

The earliest traffic tunnel in China started from Shimen Tunnel on Gubao Ramp in Shaanxi, and was built in 66 AD. After the founding of New China, in 1950s, there were only over 30 highway tunnels in China, with a total length of 2.5 kilometers. In the 1960s and 1970s, China began to build some tunnels over 100 meters on trunk highways, but the standards were very low. In the late 1980s, China really started to build expressways and expressway tunnels. The Zhongliangshan Tunnel and Jinyun Mountain Tunnel of Chengdu-Chongqing Expressway, which were completed and opened to traffic in 1990s, have increased the single tunnel length of highway tunnels in China to more than 3 000 m, and made breakthrough progress in ventilation, landslide, gas, groundwater, operation management and traffic monitoring technology, which has accumulated valuable experience for the construction of long highway tunnels in mountainous areas in China in the future. At the end of 1990s, Erlangshan Tunnel of Sichuan-Tibet Highway (465,438+060m long), Huayingshan Highway Tunnel of Guang 'an, Sichuan (4634km long) and Jiudingshan Tunnel of Chuda Expressway of Yunnan (3204m long) were opened to traffic one after another, creating the history of long mountain tunnels in China. The completion and opening to traffic of Guangzhou Pearl River Shamian Underwater Highway Tunnel and Shanghai Huangpu River Tunnel (with a total length of more than 3,000 meters) indicate that the construction technology of immersed tunnel in China has reached a new level. Chongqing Tieshanping Road Tunnel Double Line (total length of 5 424 m), Beijing Badaling Expressway Tanyugou Tunnel and Chongqing Sichuan-Guizhou Highway Zhenwushan Tunnel; Hanjialing Tunnel of Shenyang-Dalian Expressway in Liaoning Province (the widest four-lane highway tunnel in Asia), etc. It should be said that the technical level of highway tunnel construction in China is close to the international advanced level, and some of them have reached the international leading level.

From the beginning of 2 1 century, China's road network traffic gradually crossed the mountains and extended to the offshore deep water. By the end of 20 10, there were 7384 highway tunnels in China, with a length of 5 122600 m, including 265 extra-long tunnels, with a length of 165438+. Major projects such as Qinling Zhongnanshan Tunnel, Shanghai Chongming Tunnel Bridge and Xiamen Xiang 'an Submarine Tunnel have been completed one after another. The details are shown in the Annex.

Three, domestic and foreign highway tunnel construction technology and industrial development

Domestic development

China is a mountainous country, about 75% of its territory is mountains or hills, rivers and vast oceans. In recent ten years, the expressway network traffic has gradually crossed the mountains and extended to the offshore deep water. The average annual growth of highway tunnels in mountainous areas is 350 kilometers, and 28 underwater highway tunnels have been completed and opened to traffic. At the same time, in urban construction, in order to save land and protect the environment, urban road tunnels are in the ascendant, and underground interchanges have also emerged. Generally speaking, highway tunnel construction has entered a period of rapid development, and its achievements are manifested in the maturity of basic theory, comprehensive research methods, advanced survey and design technology, increasingly grand construction scale, increasingly rich structural types, mechanization of construction technology, advanced materials and complete equipment.

1. Basic theory

Since the end of 1970s, with the introduction and popularization of "New Austrian Tunneling Method" principle, highway tunnel technicians have gradually noticed the "trinity" of tunnel surrounding rock (load generation, load-bearing structure and building materials), and successfully applied it by means of controlled blasting, bolting and shotcreting support and on-site monitoring, which has improved the construction level of highway tunnels in China. Moreover, in practice, the NATM has been further developed, especially in combination with the national conditions of highway tunnel construction in China, and further exploration and research have been carried out in basic theories, such as shallow-buried excavation method.

2. Research methods.

In the early days, engineering analogy and classical mechanical analysis were the main research methods of highway tunnels. However, once the tunnel encounters complex engineering geological conditions or forms a special cross-section structure, on the one hand, it is difficult to find similar engineering precedents to learn from, and it is difficult to find a suitable classical mechanical analytical model to apply; On the other hand, the above methods alone cannot guarantee rationality and accuracy. Therefore, with the development of various technologies, the research method of numerical simulation of the whole process of tunnel engineering with the help of computers is gradually widely used. As the main research method of modern science, experimental method is undoubtedly an extremely important research method. It is a powerful weapon in tunnel engineering research, which can make up for the deficiency of numerical simulation analysis method, and the two complement each other. Generally speaking, engineering analogy method, classical analytical method, numerical simulation method and experimental method constitute the research method system of tunnel engineering, especially the latter two have become the main effective means to solve major technical problems.

3. Technical aspects of survey and design

The level of survey and design of highway tunnels has been greatly improved. The first is the progress of geological exploration means, such as the use of modern geophysical tools and high-speed geological drilling rigs. Seismic wave reflection method, acoustic wave reflection method, infrared water detection method and geological radar are generally used in the initial geological exploration and geological advance prediction in the construction stage. The integration of various geological exploration methods greatly improves the reliability of geological information; In terms of design concept, environmental awareness has been strengthened, and the principles of pre-design before construction and dynamic design of information feedback during construction stage have been popularized. Due to the use of computer technology, the stress, deformation and failure of tunnel surrounding rock, structure, stratum and adjacent structures are numerically analyzed, which provides quantitative basis for design. The popularization of computer aided design (CAD) has greatly improved the situation of drawing. On the basis of the above progress, the quality of highway tunnel design has been greatly improved.

4. In terms of construction scale.

The scale of tunnel construction is mainly manifested in the construction of many super-long tunnels and super-long flat tunnels. According to incomplete statistics, there are currently 179 extra-long mountain tunnels (including those under construction) in China. Among them, Shaanxi Qinling Zhong Nanshan Highway Tunnel, with a total length of18.02km, was completed and opened to traffic in June 2007. It is the largest double-tunnel highway tunnel in the world, and it is a typical representative of super-long highway tunnel construction technology. Long-span flat tunnels, nearly 100 double-hole six-lane tunnels have been built in China, and the construction technology is basically mature; Several two-hole eight-lane highway tunnels have been built one after another. Hanjialing Tunnel in Liaoning Province was completed and opened to traffic in 2004. It is the first single-hole four-lane highway tunnel in China. Shenzhen Yabao Tunnel was built in 2006, with the maximum excavation width of 2 1. 1m and the maximum excavation height of13.7m. It is the first two-hole eight-lane highway tunnel in China and was put into operation in 2008.

5. Structure type

In the early days, highway tunnels widely used double-hole separation structure. However, due to the limitations of various conditions, in many cases, the distance between the left and right lines of the double-hole tunnel often can not meet the construction requirements, so there are two tunnel structures: the multi-arch tunnel and the small clear distance tunnel. In addition, with the emergence of special conditions or functional technical requirements such as bridge-tunnel connection and underground interchange, the engineering practice of bifurcated tunnel structure, bridge-tunnel mixed structure and underground interchange structure is increasing day by day.

For the multi-arch tunnel, the wall type has changed from the original integral straight middle wall to the sandwich straight middle wall, and then to the sandwich curved middle wall; From symmetric multi-arch tunnel to asymmetric multi-arch tunnel, even without middle wall; From fully dark or fully bright multi-arch tunnel to light-dark combined multi-arch tunnel. Compared with the multi-arch tunnel, the small clear distance tunnel is gradually widely used because of its advantages of low engineering risk and relatively low cost. In 2004, the Fuzhou section of Beijing-Fuzhou Expressway was completed and opened to traffic, and the 14 multi-arch tunnel was changed into a small clear distance tunnel, which was the first large-scale construction project to promote the small clear distance tunnel in China.

In order to solve the problem that the bridge and tunnel are close to each other, a new structural type-bifurcated structure is developed, which can be divided into two types: the first one gradually transits from the multi-arch structure section and the small clear distance structure section at the entrance to the normal double-hole separated structure; The second type of entrance section is first set as a four-lane large arch, then gradually transformed into a multi-arch tunnel and a small clear distance tunnel, and finally transformed into a standard two-hole separated tunnel. The Baziling Tunnel of Hubei Hurongxi Expressway completed in 2007, the Yuehuquan Tunnel and Paipan Tunnel of Shanxi Jinji Expressway opened to traffic in 2008 are typical projects. Especially in Paipan Tunnel, in order to adapt the whole bridge structure to extend into the tunnel, a special mixed structure of upper and lower double-deck bridge and tunnel was developed, with the maximum excavation span of 25.77m, rise-span ratio of 0.35 and cross-sectional area of 346.6m2.

Because the underground interchange can reduce the demolition, protect the environment and directly realize the traffic conversion between underground tunnels or between underground tunnels and ground roads, this type of structure has also appeared in recent years. Shiwanshan Tunnel and Zhonggushan Tunnel in the first phase of Xiamen Airport Road are completely connected, which is the first tunnel with underground interchange structure in China and was completed in September 2008. This section has both plane bifurcation structure and up-and-down cross structure. The maximum excavation span of a single hole is 25.89m, the thickness of rock inclusions in the small clear distance section is only 1.42m, and the multi-arch section is an asymmetric multi-arch structure. Xiangjiang Tunnel on Yingpan Road in Changsha, which started in August 2009, also introduced the underground interchange structure into the underwater tunnel project for the first time.

Due to the deepening of related research and the urgent need of engineering practice, the limit values of surrounding rock thickness and middle wall thickness of multi-arch tunnel with small clear distance are constantly refreshed. With the development and practice of a number of new structural types, the structural types of tunnels are enriched and the vitality of tunnel engineering is enhanced.