On the morning of December 11, 2020, the Beijing Metro Line 8 Phase III project between Qianmen Station and Wangfujing Station achieved a two-line connection, which marked the completion of the Metro Line 8 tunnel section project that runs through the north-south central axis of Beijing.

Track laying construction is planned for June 2021

Beijing Metro Line 8 runs north-south, basically coincides with the central axis of Beijing, and is a backbone line running north-south in the line network planning. Due to the late start of construction in the central city section and the difficulty of construction, this line currently runs in two sections, north and south. The northern section starts from Zhuxinzhuang Station in Changping District in the north, to the National Art Museum Station in Dongcheng District in the south, and the southern section starts from the east in the north. Zhushikou Station in the urban area, south to Yinghai Station in Daxing District.

The Beijing Metro Line 8 project is divided into four phases. The first phase (Olympic branch line) was started in 2005 and opened to traffic in July 2008; the second, third, and fourth phases of construction were subsequently carried out, and the opening to traffic status was achieved by the end of 2018 . At present, there are three remaining Wangfujing North Station, Wangfujing Station, Qianmen Station and the corresponding two sections of Line 8 which are about 3.56 kilometers in length. Due to the late start of construction and the difficulty of construction, the construction is still underway.

The section to be penetrated this time is the last section of Beijing Metro Line 8. It is 1.65 kilometers long and is constructed with a mud-water balance shield machine. The shield machine starts from Qianmen Station and goes along Qianmen East Street and Taijichang Street. Received on the south side of Chang'an Avenue. According to Lu Gaofeng, deputy general manager of the First Project Management Center of Beijing Railway Company, since this section is located in the core area of the city, construction is relatively late. It is expected that the electromechanical installation will start after the Spring Festival in 2021, and the track laying will be carried out in June 2021.

Repair the subway archeologically

Judging from the engineering roadmap, the shield section needs to pass through two special risk sources, including the National Railway Diameter Line and the existing Metro Line 2, as well as the China Railway Museum, the Capital Planning Exhibition Hall, the site of the French Embassy, and the site of the French Barracks. Waiting for 20 first and second risk sources, this section of the tunnel is the section with the most risk sources in the construction of Beijing subway. According to the construction party, “almost all the way past are cultural relics, which are sources of risks, and the requirements for settlement control are extremely high”.

According to the construction party, the shield machine has experienced a difficult "journey" after it departed from Qianmen Station. First, it continued downhill from a depth of 32 meters to a maximum buried depth of 42 meters. This is the deepest buried section of the Beijing subway at present, and all of them are located in sandy gravel formations with high permeability coefficients. The groundwater level is up to 14 meters, and the ground is not available. For maintenance and tool change conditions, the tool needs to be pressed into the warehouse for maintenance and tool change, which increases the risk of technical operations.

In order to ensure that the construction is foolproof, the construction team adopted archeological construction, taking great care every one meter forward, using the most advanced mud-water balance shield machine to control surface settlement, and using a series of technical research to protect ground cultural relics and important facilities.

According to Wang Zhaomin, the person in charge of the construction bid section of the project, the project takes full advantage of the comprehensive technical advantages of subway shield construction in the core area of big cities, through three-dimensional visualization and real-time display, precise grouting of key construction parts, establishment of remote intelligent monitoring of shield operation, and strict compliance with The design requires adjustment and control of synchronous grouting, compensation of grouting pressure and grouting volume. At the same time, the mud suppression effect is used to fill the gap between the size difference between the cutter head and the shield shell, and the settlement factors are eliminated one by one, and all risk sources are successfully overcome. During the construction period, the two shield machines went under the super risk source four times, and the structural settlement was less than 1 mm, which was called "zero settlement". The project team has also developed a micro-disturbance control technology for long-distance continuous tunneling through sensitive buildings in central urban areas.

Environmental protection construction in the core area, zero pollution and zero movement

Since the project entered the site, fully enclosed management has been adopted. The muck piles, shaft heads, and mud-water separation stations are all wrapped in enclosed sheds to minimize the spread of dust and construction noise. The project is only 50 meters away from Tiananmen Square. Even if the surrounding tourists are weaving every day, they will not feel that the large-scale project is under construction.

Faced with about 1,600 tons of mud entrapped in the mud excavated every day, the construction team filtered the mud that powers the shield through the mud-water separation system. An automated mud weighing system was installed at the equipment outlet to accurately count the excavation. The amount of slag can help judge the rationality of the tunneling parameters and ensure construction safety. The filtered mud can be recycled to realize the conversion of waste into treasure for in-situ disposal. The sand and gravel treated by the mud-water separation equipment will be transported by a special muck transport vehicle to a special muck disposal site at night, which can be used as Synchronous grouting materials, roadbed fillers, etc. are used, and the construction has achieved "zero waste".

In the future, when the Beijing Metro Line 8 is fully opened to traffic, it will help to open up the north-south public transportation artery and further optimize the rail transit pattern. Editor/He Yuting