In April 2012, a busy worker (Chen Zhuo) on the subway construction site

1 Geology: "Eight Treasure Porridge" is soft, hard and thin.

Yangtze River , Han River passes through the city, lakes and fish ponds are dotted around the city, and the underground situation in Wuhan is so complex that it was once identified by experts as "a city not suitable for building a subway."

In the words of experts, Wuhan’s geology is like “eight-treasure porridge”—soft, hard, thin, and thick; fine sand, pure clay, charcoal caves, sandstone, mudstone, and Underwater operations. During the excavation process, Metro Line 2 basically passed through all geological types and overcame difficulties along the way.

The most difficult thing to conquer is the Yangtze River. 55 years ago, Wuhan crossed the Yangtze River. 55 years later, Wuhan completed a subway tunnel crossing the Yangtze River.

While successfully crossing, Line 2 has left Wuhan with five national firsts: the first subway tunnel crossing the Yangtze River in China; the longest single-head tunnel tunnel in China; the deepest buried depth in China The largest subway tunnel with a deepest depth of 46 meters; the subway tunnel with the highest water pressure in the country; the first domestic tunnel with a pump room communication channel built under the river.

Wuhan Geology

Fine sand, pure clay, charcoal cave, sandstone, mudstone, etc.

2 Technical hurdle: Working with high water pressure against a hill

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The same is true for subway digging. Few cities in China face as many technical difficulties as Wuhan.

The tunnels between Hankou Railway Station and Fanhu Station on Line 2 all pass through the gas reservoir.

The Metro Group said that when tunnel construction approaches or excavates the gas layer, the gas will flow into the tunnel, burn and explode in case of fire. If the concentration is too high, it will cause suffocation and death, which has always been considered A "restricted zone" for subway construction.

Wuhan subway construction adopts "no mobile phones going down the well", "high-power exhaust fans and exhaust fans operate 24 hours a day", and "a gas monitoring system is installed on the head of the shield machine. Once the concentration exceeds the standard, the entire operating system will automatically Cutting off power and forcing ventilation" and other measures, the shield machine successfully crossed.

“When digging tunnels under the river, high water pressure and large burial depth pose great challenges to the adaptability of the shield machine.”

When the shield machine is sneaking under the river, the water pressure is the highest, and the water and soil pressure on the machine is even as high as 0.6MPa, which is "equivalent to working with a hill on your back."

What’s more difficult is that the shield machine is passing through the sand layer at this time, and its resistance to deformation is poor, so the sealing must be "harsh".

The construction party customized the shield machine. "The shield tail is lengthened by nearly two meters. The longer the shield tail, the more sealing air cushions and shield tail brushes in the shield tail oil area, and these fillings can prevent water leakage." Ni Zhengmao, head of the Metro Group's river-crossing project, said: "In the end, Wuhan passed the test, and the shield machine crossed the Wuchang Embankment in just one and a half days."

Technical difficulties

Crossing the reservoir Digging tunnels in gas layers and river bottoms

3 Funding barriers: "Combined boxing" costs hundreds of millions of yuan per kilometer

Building a subway in a city that is "unsuitable for subway construction" is very costly. Raising money is more difficult.

The Metro Group introduced that the total estimated investment for the first phase of Metro Line 2 alone is 15.46 billion yuan. While Line 2 is being built, Wuhan must speed up the "catch-up" and several lines must be rolled out at the same time. , the financial pressure is more obvious.

“Lines 1, 2, and 4 are 72 kilometers long and require an investment of more than 20 billion yuan. The city government has tried its best to provide 500 million yuan in capital, but the gap is very large.” Chairman of the Metro Group Tu Heping said.

Asset leasing, equity financing, bank loans... Wuhan Metro has launched a series of "financial combination punches" to bring together all parties.

At the end of December every year, the Metro Group must pay off the bank loans and interest for that year, otherwise it will become a "black account" and it will be difficult to borrow money. Liu Yuhua, general manager of the Metro Group, said: "To me, this day is like the so-called 'doomsday'. This year, we will have to pay back 650 million yuan."

Based on the total investment of Metro Line 2, The cost per kilometer is hundreds of millions of yuan. Liu Yuhua once laughed and said that his "signature" is very valuable, "My daily payment limit is 50 million yuan."

Financial requirements

The first phase investment of Line 2 is 15.46 billion yuan

The total length is 27.7 kilometers, and the cost per kilometer exceeds 500 million yuan

4 Demolition barriers: Many objects in urban areas are faced with difficulties in project demolition, and the demolition of Metro Line 2 is even more difficult.

“Places that need to be demolished are distributed in various urban areas, including central government units, provincial agencies, individuals, enterprises... Subway Line 2 can meet almost all types of demolition targets.” Many subway groups All the comrades in charge of the demolition felt this way.

Ma Ruijun, deputy secretary of the Party Committee of the Metro Group, said that construction of Line 2 started in 2007, but until the "Several Opinions on Accelerating the Construction and Development of Rail Transit" was issued in May 2008, the demolition was "slowly advanced."

This "Opinion" overturns the original "demolition model" and innovatively proposes that each district government is "mainly responsible" for the demolition along the tracks within its jurisdiction. The municipal government issues a demolition quantity target every year, and the Metro Group Provide funding. At the end of the year, subway demolition entered the target assessment of each district. That year, Line 2 completed the demolition of hundreds of thousands of square meters. Previously, the demolition amounted to only "tens of thousands of square meters" every year. This innovation has been copied by Xi'an.

At present, the "upgraded version" of the "Opinions" has been completed, and the municipal party committee and municipal government are about to issue the "Several Opinions on Further Accelerating the Construction and Development of Rail Transit."

New model of demolition

Each district government is "mainly responsible" for demolition along the tracks within its jurisdiction. The municipal government sets a target for the number of demolitions every year, and the Metro Group provides funds

5 Safety Gates: Establish Four Shields to Prevent Dangerous Situations

While Wuhan Metro Line 2 is advancing bravely, news of subway construction accidents in other domestic cities often comes from time to time.

“Since the construction of the first phase of Line 2, there have been no major safety incidents,” the Metro Group said yesterday.

"Precise preparation before construction and the formulation of detailed emergency plans" are two powerful tools for Line 2 to "move forward safely".

Reinforced concrete walls are built around the subway station, which is very strong, but the shield starting shaft requires a round hole with a diameter of more than 6 meters, which undoubtedly becomes the weakest link.

“Once there is a problem, groundwater and sediment will flow into the subway station from the round hole, and it only takes a few hours to submerge the subway station and TBM. Such an example is in a coastal city ever performed”.

In order to prevent danger when the shield machine enters and exits the station, Wuhan Metro Construction "sets up" four protective measures, like four shields, to ensure safety. In addition, each construction party has also prepared emergency plans and reserves a large amount of emergency supplies.

Only in the river-crossing section of Line 2, the shield machine had to "enter three times and exit three times." Each time, it was like steering the ship at the cusp of the storm. In the end, there were no problems with the shield machine.

Safety "sharp weapon"

Precision preparation before construction

Develop detailed emergency plan

6 Docking Points": "Golden Pole" Proactively come to the door for repeated modifications

Line 2 is known as the "golden pole" in a prosperous city. "If it is not well connected with the units along the line, the 'golden pole' will become a 'rotten hemp rope.'" .

“Digging underground only requires overcoming technical difficulties, but trying to get out of the ground requires facing more difficulties: some units will not cooperate, and some units will require conditions for you to connect with them.

The Metro Group contacted the design institute and made multiple modifications to the design of the docking of subway stations along the line, trying to achieve " docking " of shopping malls, hospitals, parks, stations, underground crossings and other facilities with subway entrances and exits.

During the construction of Zhongshan Park Station on Line 2, Union Hospital was building a new building. Both major projects required the excavation of deep foundation pits, which were so close that there were great safety risks.

The Metro Group took the initiative to "connect" with the hospital. After coordination between the two parties, the construction period was staggered and the construction of the channel was scientifically divided. After the subway station was completed, Union Hospital was "connected" to the subway with three passages: a fire corridor and two pedestrian passages. Citizens can reach each floor of Xiehe Clinic Building by taking the elevator from the subway exit.

Comprehensive docking

Try to achieve " docking " of shopping malls, hospitals, parks, stations, underground crossings and other facilities with subway entrances and exits

7 Construction issues: multiple solutions required "Construction will continue"

Line 2 passes through the prosperous areas of Wuhan, the subway station needs to be constructed, and the traffic must be ensured. The construction company worked together with the traffic control department to formulate various construction plans to minimize the impact on urban traffic.

In the Zhongnan Road subway station, Line 2, Line 4 and Line 4 are "parallel" here. The station is almost as wide as Zhongnan Road.

"How to encircle it? Enclosing it all will interrupt the traffic on Zhongnan Road, which means the entire Wuchang traffic is paralyzed." The Metro Group and the China Railway 19th Bureau adopt the "half construction and half traffic method", and the half enclosed is too It was too narrow to be constructed using the relatively fast excavation method, so the workers first built the ground cover for half of the road, then dug down bit by bit from the side to build half of the station. Then adjust the side and continue to use the difficult method of digging from below to build the other half of the station.

Zhongnan Road Station is almost the station with the longest construction time on Line 2. During the construction period, three lanes on the ground were always maintained to ensure "continuous construction" of this fragile Wuchang traffic artery.

The Wangjiadun East Station at the Qingnian intersection of Jianshe Avenue is located at an important crossroads. The Huangxiao River box culvert will be temporarily relocated below the station. In order to ensure traffic, the China Railway Fifth Bureau "divided" the three stations at this intersection. "It is divided into three sections, and the surrounding construction is carried out in three times.

Construction method

"Half construction and half traffic method": first build half of the road's ground cover, dig down from the side to build half of the station, and then build the other half on the side Station

Metro Line 2

The most under construction

The most worrying

Two dangers occurred under the Yangtze River

In August 2010, during the construction of the cross-river tunnel, the shield machine on the right line (that is, from Wuchang to Hankou) encountered an abandoned drill pipe. When the shield machine cut it, one tool fell off and two other tools fell off. A gap appeared, and the technician replaced the tool at great risk. In October of that year, the left-line shield machine encountered two steel pipes and was unable to move forward. The shield machine cannot turn at will, it can only find a way to cut the steel pipe. Cutting under pressure is extremely risky, and there is no such technology in China. Finally, four engineers were hired in Germany to enter the cabin and cut the steel pipe.

The most innovative

The 49-meter-deep "ice tube" is built at the bottom of the Yangtze River

The subway tunnel is divided into two independent lines on the left and right, parallel to each other. There is a communication channel to facilitate passengers to transfer from the accident tunnel to another safe tunnel in case of emergency. Building a communication channel at the bottom of the river, which is more than 49 meters underground, has never been done before in the country.

Opening a subway tunnel under a river is extremely risky. If you are not careful, river water will flow into the subway tunnel. The construction team needs to bury freezing pipes between the two tunnels to form a minus 30°C "ice tube" around the tunnel. Then the center of the "ice tube" is hollowed out and poured with concrete to form a communication channel.

The most difficult to repair

Hongshan Square Station is too big

Jianghan Road Station is too deep

Among the 21 stations of Wuhan Metro Line 2 , the most difficult ones to repair are Hongshan Square Station and Jianghan Road Station. The former is too large and is difficult to excavate directly, while the latter is too deep and drainage is very difficult.

The Hongshan Square subway station has a construction area of ??nearly 60,000 square meters. If excavated directly, the area of ??the deep foundation pit will exceed 10,000 square meters. Inadequate protection or insufficient pumping will endanger surrounding buildings and the square in use. Underpass. Jianghan Road subway station is located on the bank of the Yangtze River. It must be dug deeply so that the subway tunnel does not have to be so steep. The station is 26 meters deep underground. During the construction process, it encountered the danger of groundwater influx. Fortunately, the construction team handled it properly and no serious consequences were caused. Reference materials adopted