Key points of safety and quality in tunnel constru

2022-08-19
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The construction of railway tunnels in China has experienced a history of nearly 120 years from the late Qing Dynasty to the present. During this period, the survey methods and design theories of railway tunnels have been constantly updated, the construction methods and technical equipment have been continuously improved, and the technical standards have been continuously improved. By the end of 2006, China has successfully built more than 7500 railway tunnels with a total extension of more than 4300 kilometers, and the number and total length of tunnels are among the highest in the world. The construction of railway tunnels in China has achieved a qualitative leap because its material has a rigidity comparable to that of metal. In terms of high-speed railway tunnels, we have mastered most of the key technologies and preliminarily formed the construction standard of China's high-speed railway. During the "Eleventh Five Year Plan" period, China will build 17000 kilometers of new railways, including 7000 kilometers of passenger dedicated lines. In the passenger dedicated line projects under construction and proposed, the total length of the designed tunnel is 1000 kilometers, and more than 3000 kilometers of railway tunnels will be built in the next few years

the Shijiazhuang Taiyuan railway has 32 tunnels with a total length of 74.58 kilometers, including the Taihang Mountain tunnel, the largest railway tunnel in China so far, with a total length of 27.839 kilometers and designed as a double hole single track

Wuhan Guangzhou passenger dedicated line has a design speed of 350 kilometers per hour, a total of 224 tunnels (including open cut tunnels), with a total length of 172.952 kilometers, accounting for 18.81% of the total line length, and 12 connecting line tunnels, with a total length of 3.802 kilometers. The longest tunnel in the whole line is Liuyanghe Tunnel, which is 10.115 kilometers long

Zhengzhou Xi'an Passenger Dedicated Line is located in Henan and Shaanxi provinces. There are 4 tunnels in Shaanxi Province, with a total length of 13.7 kilometers. The longest Qindong tunnel, with a length of 7691m, is a loess tunnel. There are 22 tunnels in Henan Province, with a total length of 31.022 kilometers, including Zhangmao tunnel with a total length of 8460M. The Loess double track tunnel Hanguguan Tunnel, which is difficult, is 7851m long

Hefei Wuhan railway passenger dedicated line starts from Hefei in the East, passes through Lu'an, Macheng, and Wuhan, and crosses the hinterland of the Dabie Mountains. It is an important part of the Shanghai Wuhan Chengdu Expressway planned by the state. The total length of the line is 357 kilometers, and the total length of the control project Dabie Mountain tunnel is 13253 meters; There is also Jinzhai tunnel, with a total length of 10700m

the cumulative length of tunnels on other lines is 280km in Ningbo Wenzhou Fuzhou Xiamen, 15km in Beijing Shanghai Expressway, 80km in Wuhan Hefei and 300km in Wuhan Chengdu

in order to overcome the aerodynamic problems caused by the operation of high-speed trains in the tunnel on the passenger dedicated line, most of the tunnels on the passenger dedicated line pass through the double track railway tunnel, the distance between the tunnel lines is 5m, the effective area above the rail surface is 100m2, and the excavation area is 140 ~ 170 m2, which is a super large cross-section tunnel. The distance between double hole single track lines is 35 m, and the effective area above the rail surface is 60 m2,. In order to help alleviate the aerodynamic effect, the cutting type is the dominant form of the portal structure

(I) characteristics

1. The large section of the tunnel increases the difficulty of construction, especially for the construction of weak surrounding rock and unfavorable geological sections

under the condition of high-speed operation, the requirements for tunnel technology are mainly aerodynamic characteristics (driving resistance, transient pressure, micro pressure wave, train wind force, etc.), and the adverse effects on driving, passenger riding comfort, train related performance and portal circulation are very obvious. Therefore, when the speed of high-speed railway reaches 300 ~ 350km/h, the effective area of single line tunnel is 70m2, and that of double 4. Whether the operation is simple line tunnel is 100 m2. Due to the expansion of cross-section and the increase of long tunnels, the difficulty of tunnel construction increases, which often becomes the key project to control the construction period of the whole line

2. High technical standards

due to the large cross-section, complex stress and high train speed, the tunnel maintenance is limited, and the requirements for the safety, durability and waterproof performance of the tunnel lining are improved. In order to highlight "strengthening the base" and pay attention to the principle of stiffness change, the lining of grade III ~ V surrounding rock adopts inverted arch structure, and the thickness of inverted arch is larger than that of arch wall. The bottom plate of grade II surrounding rock tunnel adopts reinforced concrete structure, and some underground water development sections also adopt inverted arch structure. Reinforced concrete structure is adopted for the lining of class IV, V surrounding rock and class III surrounding rock eccentric pressure section. The basement of weak surrounding rock must be reinforced. The requirements for construction technology are higher, such as full width pouring of inverted arch, and demolition of arch wall formwork is allowed only when the formwork removal reaches more than 8Mpa. Set up a reliable disaster prevention and rescue system, and adopt the portal form that is conducive to mitigating the aerodynamic effect. The portal design should not only meet the requirements of structural safety, stability, environmental protection and landscape, but also meet the requirements of the structure to mitigate the impact of micro air pressure waves. The cutting portal structure has become the main tunnel form

3. The construction environment is poor

the working space is narrow, with the characteristics of surrounding rock leakage, air pollution, high noise and difficult lighting

4. The surrounding rock of the tunnel is complex and changeable, and the construction method has varying uncertainties, which increases the difficulty of construction organization

5. The geological and hydrogeological changes of the tunnel are difficult to respond correctly in the design, and the survey and design methods are not easy to reach the quantitative standard. Many of them are judged by empirical data, which is quite different from the actual disclosure

(II) principles to be followed in tunnel construction

the construction of passenger dedicated tunnel shall be organized in accordance with the guiding ideology of "fast, high quality and high efficiency" and the principle of "protecting surrounding rock, being solid inside and beautiful outside, paying attention to the environment and dynamic construction". Make the tunnel construction conform to the purposes of advanced technology, excellent quality, construction safety, balanced progress, reduced consumption and environmental protection

(III) basic tunnel construction methods

the selection of construction methods is mainly the selection of excavation and transportation methods. Since this is related to the future development ideas of enterprises and the strategic layout direction, the methods can be divided into drilling and blasting method, excavation method (tunneling machine method, shield method, tunneling machine supplemented by drilling and blasting method), and buried pipe section method (underwater tunnel)

the following is mainly about the drilling and blasting construction. The auto parts testing machine has flexible and diverse control methods

1. Guiding ideology for selecting construction methods

(1) ensuring construction safety and improving construction environment

(2) it should be determined according to the design documents, construction investigation, surrounding rock level, combined with tunnel length, section size, construction period requirements, equipment level, team quality and other comprehensive factors

(3) tunnels with large geological changes should consider their adaptability for easy adjustment

(4) new technologies, processes, equipment and materials should be used as much as possible

(5) carefully follow the NATM construction principles, and master and apply the three elements of smooth blasting, shotcrete and anchor, and measurement construction

2. Basic construction methods of passenger dedicated tunnel

basic construction methods of passenger dedicated tunnel include: full section method; Step method; The divisional excavation method of NATM includes: middle diaphragm method (CD), cross middle diaphragm method (CRD) and double wall heading method (also known as glasses method)

for hard rock, full section method and bench method should be adopted. The divisional excavation method is suitable for soft rock, and the bench method should not use long bench, because it is not conducive to the early sealing and looping of initial support. The blasting of hard rock tunnel will seriously damage the formed middle wall (or middle wall)

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