In a shaft 40m below sea level, when you put your ear against the shaft wall, you can hear the sound of the shield machine approaching gradually, and then return to silence.
From a shaft 70m deep below the ground level, a φ9.1m mud-water shield was launched. The undersea tunnel used for piping at the Tokyo Gas Fanjima Plant, the deepest in Japan, dug 530m into the subsea strata before reaching the undersea shaft, and the shield machine stopped in an instant.
This shield machine excavation project was carried out within 6 months from March 6, 1995 to September 8 of the same year, including shaft construction, sinking, shield starting and arrival protection After waiting for preparatory work, it took 21 months and under a high water pressure of 700KPa to complete a shield tunnel that was completely impervious to water leakage, becoming another proof that Japan’s shield construction technology is at the world’s top level.
The origin of shield tunneling was in 1818, when the British M.I. Brussels set up a 21m-deep working pit on the bank of the Thames River in London, using a "shield tunnel" to push out the barrier. The earth structure uses the back wall of the working pit as the supporting wall, and uses the screw jack as the propulsion power to advance this "earth-retaining shield". On the way, it was interrupted due to river bed soil collapse and flooding accidents. It actually took more than 20 years to complete the tunnel. At this time, Brussels, the founder of the TBM, was already 72 years old. The shield tunneling method that has developed to this day is the result of Brussels' enthusiasm spreading to the top.
After that, in the South London Railway Tunnel Project in 1887, shield propulsion using the pneumatic construction method was also used, laying the foundation for the shield construction method.
By the 1890s, most countries such as the United States, Germany, and France also used the shield tunneling method in tunnel construction. Semi-shields (roof shields), oval, horseshoe, rectangular and other shields are also used.
In Japan, by learning from European and American technologies, the shield tunneling method was used in the construction of subway, sewers, etc. starting in about 1940. After 1970, the closed construction method was developed, and there has been a rapid development. . In the Trans-English Channel Tunnel project in 1989, an earth pressure shield machine made in Japan was used, which is leading the world until today.
The following describes the introduction and development of the shield tunneling method in Japan, as well as its future prospects.
Japan’s shield tunneling method
1. Introduction and development of shield tunneling method
The first successful shield tunneling method in Japan was the National Railways Kanmon Undersea Tunnel In the project (1939-1944), a φ7.2m manual excavating shield machine was used in the 405m upward line and 725m downward line on Moji's poor foundation, using both the pneumatic construction method and the chemical liquid grouting method. Construction was carried out. Through this project, it can be considered that Japan’s shield tunneling technology was established.
Roof shields were used in the Kanmon Expressway Tunnel in 1953 and the Nagatacho 2 Work Area of ??Teito Expressway Line 4 in 1957. Furthermore, the Kakuoyama Subway in Nagoya City was used. The tunnel was constructed using manual excavation and shield tunneling using the pneumatic construction method.
After that, due to the rapid economic development in preparation for the 1964 Tokyo Olympics, urban facility construction projects were required to increase dramatically, and the pollution caused by construction projects sometimes became apparent. The use of manual excavation shield construction method has replaced the previous open-cut construction method in urban tunnels. During this period, along with the shield tunneling, precipitation engineering methods and air pressure engineering methods were used as measures to deal with groundwater, and auxiliary engineering methods such as chemical liquid grouting were also used as measures to deal with foundation settlement.
While the shield tunneling method is popularized, it is hoped to develop a shield tunneling method that can shorten the construction period, save labor, and deal with problems such as complex foundations. The mechanical tunneling shield tunneling method was used in the Osaka City Waterway in 1963. The new shield tunnel was first used in the Dadian Water Pipeline (φ2.6m, length 227m). The following year, in the Osaka City subway project, the large-section mechanical tunneling construction method with a diameter of 6.97m and a tunneling length of 668.4m was used. Various manufacturers and companies are committed to the development and practical use of mechanical tunneling shield machines. transformation stage.
2. Development of closed shield construction method
As a result of the use of pneumatic construction method or chemical grouting method as an auxiliary construction method, hypoxia accidents and chemical slurry damage accidents may occur Or fire accident in tunnel. The search for countermeasures against these accidents led to the birth of mud-water shield tunneling and earth pressure shield tunneling methods.
The principle of mud-water shield was conceived in 1961 by the French company Camino Peronate, and in Japan it was used for Line 9 of the Teito Expressway Transportation Corporation Subway in 1967 The mud-water shield construction method has been used in the diversion tunnel (φ3.1m, length 312m) of the Kanda River Works District main line project. The mud-water shield construction method is to keep the cutting cutterhead part of the mechanized shield unchanged, seal it with a partition wall, use pressure to send mud water to the excavation surface, and use a mud discharge valve to fluidly transport the excavated soil ballast. As a large tunnel section, in 1969, the Haneda Tunnel of the Keiyo Line of the Japan Railway Construction Corporation adopted a φ7.29m, 856m×2 line project in the Morisaki Canal Works Area, which attracted the attention of foreign people. of greater concern.
In addition, Japan independently developed the earth pressure shield in 1974. This shield construction method also has a partition wall behind the cutting head of the mechanized shield machine, uses a screw conveyor to discharge the soil, and mixes the excavated soil in the closed cabin into soil through a mixing and stirring mechanism. The specified pressure is used to obtain the stability of the excavation surface. As an improved version of the earth pressure shield tunneling method, the mixed soil pressurized shield tunneling method is developed by injecting additive materials (slurry materials, mud materials) into the closed chamber of the cutter and using a stirring impeller. The earth pressure shield tunneling method The scope of possible applications of construction methods is gradually expanding. The soil pressurized shield construction method was first used in the water pipe construction project in the Tokyo Metropolitan Waterworks Bureau's local area in 1976. The additive material used is a bubble (foam) shield tunneling method that uses air bubbles to improve the fluidity and water-stopping properties of the excavation soil.
Closed shield tunneling methods such as mud water type and earth pressure type improve the atmospheric pressure working environment in the construction tunnel. There are no longer problems such as air leakage and lack of oxygen. Environmental protection is guaranteed, and it has become the mainstream of shield construction methods in the future.
3. Diversification of shield tunneling methods
Due to the practical implementation of the closed shield tunneling method, the impact on the surrounding environment such as the stability of the excavation surface and foundation settlement has become smaller. , the shield construction method has become the main force in dealing with unfavorable construction conditions for large-scale tunnel projects such as underground railways, water supply and sewers, power communications, roads, and underground rivers.
In addition, when entering the second half of the 1980s, there were various needs for the scale, shape, alignment, automation, labor saving, cost reduction, etc. of these tunnels, and projects were carried out. The dynamics of technology competition between general contractors and manufacturers.
(1) Large cross-section
In order to overcome the problems of stabilizing the excavation surface and improving the efficiency of materials, machinery, and material combinations, we started with the φ14.14m road across Tokyo Bay. , the institute has carried out the construction of large-diameter tunnels such as large-section railways, highways, and underground rivers.
(2) Greater depth
Since the relatively shallow underground spaces in the city are occupied by existing structures, new tunnels must be deeper, so the construction depth must be lower. For a 60-70m tunnel, it is necessary to improve the pressure-bearing capacity and durability of the shield machine and segments, which are necessary conditions for construction at large depths and high water pressure.
(3) Long distance
In overly dense urban areas, when it is difficult to secure land for shafts, through the effective use of shield machines and other functions, the reduction of The cost target requires the use of a shield machine for long-distance excavation. In this case, there are issues such as the durability of the shield machine, the replacement technology of the cutting head, the processing equipment for excavation and ballast, and the equipment for transporting materials and equipment to the excavation surface at high speed. There are actual results of projects with a construction length of 6.5km.
(4) Optimization of cross-section
Usually, the engineering cost is directly proportional to the excavation cross-section. In addition, subject to the constraints of the land, a shape that can meet the purpose of use must be obtained. Minimize the cross-sectional area of ??the tunnel.
In response to such needs, MF, DOT, H
(5) Tunnel lining and underground docking technology have been continuously developed. As one of the technological developments to shorten the construction period and reduce the cost, Instead of using prefabricated segment lining blocks, the ECL construction method was developed. Instead, formwork was set directly in the shield and the tunnel lining was poured on-site. In this case, the shield machine that tunnels in from both sides will perform shield joining technology in the ground, and projects such as the ground soil freezing construction method and the MSD construction method will be developed.
4. Evaluation abroad
In several major sections of the Channel Tunnel (length 49km) project opened in May 1994, in the design, production, maintenance In other aspects, Japanese shield machines are fully used.
What has been passed down are excellent construction achievements. Japan’s shield technology and the efforts of relevant personnel who have been engaged in this field for a long time have become the targets of overseas evaluation.
Future technical issues and prospects
According to the development of large-depth and large-section tunnel excavation technology represented by the Channel Tunnel or the undersea tunnel across Tokyo Bay, and the development of large-scale tunnels in large urban areas, In the context of the difficulty of securing land for internal infrastructure, the "Special Measures for the Use of Large-depth Underground Parkway" was established in May 2000, and underground development technology once again attracted people's attention.
In particular, there are great expectations for the shield tunneling method for long underground structures such as railways and highways. In the future, it is expected to be safe, high-speed, and safe while ensuring quality. Technology development aimed at low-cost construction. Specifically, the following technical issues can be cited.
Large depth (sealing, departure, arrival methods, earth discharge mechanism of shield machine, etc.)
Large cross-section (direction control of shield machine, segment joints) , assembly method...)
Long distance (transportation of excavation and ballast, transportation of segments, repair and replacement of cutting heads, safety and health of workers...)
Disposal of ground obstacles (removal of foundation piles of original structures, wooden sections, etc.)
Construction in the city center (compacting of temporary facilities on the ground, reducing noise and vibration...)
Recently, as one of the new shield tunneling methods, the idea that several shield tunneling machines must be used as a whole to excavate and to be able to arbitrarily branch underground road ramps and other reasonable construction has been announced. We can see the signs of advanced shield tunneling technology. Regarding the needs of society, we look forward to further research results by technical personnel.
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