How to pour flood water into Zhengzhou Metro?

The increase in urban area leads to insufficient drainage capacity of the municipal pipe network?

How to pour flood water into Zhengzhou Metro?

Author | Chen Fuye Editor | Yang Puding

Production | Prism· Tencent News Xiaoman Studio

How to pour flood water into Zhengzhou Metro?

Line 5 is one of the busiest lines of Zhengzhou Metro. According to “Zhengzhou Metro” official micro, July 20 this day, total passenger traffic reached No. 5 line of 347,200 people, is the day the most passenger traffic of a line.

How to pour flood water into Zhengzhou Metro?

Picture from “Zhengzhou Metro”

This subway, which was fully operational on May 20, 2019, plays an important role in Zhengzhou’s subway map. It is a peripheral edge of the core area of the city loop line, a total length of 40.43 kilometers, a total of 32 stations, will be closely divided railroad town in the old together , is that many office workers should always carry vehicles.

At around 6 pm on July 20, at the peak of the off-duty period, this subway suffered “two hours of life and death” between Beach Temple Street Station and Shakou Road Station.

According to the official microblog of the “Zhengzhou Release”, since July 17th, Zhengzhou has experienced a series of unusually heavy rainstorms, causing serious water accumulation in the Wulongkou parking station of Line 5 and the surrounding area. At 18:00 that day, the stagnant water smashed the retaining wall of the entry line and entered the main line section, causing the trains of Line 5 to be suspended at the tunnels of the Beach Temple Station and Shakou Road Stations.

“Zhengzhou Release” posted a Weibo at 3:50 on the 21st, stating that the Zhengzhou Metro organized forces to evacuate more than 500 people, of which 12 died and 5 were injured.

The subway has become a standard configuration in many large cities. Affected by extreme weather, rainwater in the subways in some cities occasionally occurs, but it is rare that subways are trapped between tunnels by heavy water. According to the “National Emergency Plan for Urban Rail Transit Operation Emergencies”, the current casualties are classified as “major operational emergencies”, second only to “particularly serious”.

According to the People’s Daily report on July 21, the Emergency Management Department immediately initiated the cross-regional reinforcement plan for fire rescue teams and dispatched fire rescue and water rescue professionals in Hebei, Shanxi, Jiangsu, Anhui, Jiangxi, Shandong, and Hubei overnight. A team of 1,800 officers and soldiers, 250 boats, 7 sets of “dragon water absorption” high-power flood drainage vehicles, 11 sets of remote water supply systems, and more than 18,500 pieces (sets) of flood rescue and rescue equipment rushed to emergency flood control and disaster relief in Henan.

How to pour flood water into Zhengzhou Metro?

The water reaches the chest

The netizen “Miracle Romance” was the victim of the accident. She told about her experience on Weibo.

At four o’clock in the afternoon of the same day, the company’s property noticed that there was a power outage, and employees needed to leave work as soon as possible. When she and her colleagues went downstairs, they found that the stagnant water at the door had reached her knees, and she hesitated to pass it. After more than an hour, the rain showed no signs of abating, so she decided to wade across the water and got on the subway.

According to her description, just after one stop on the subway, she couldn’t walk and stopped in the tunnel. Soon, the water began to slowly seep into the carriage. Many passengers stood on their seats, but the water still reached their chests. What made her feel more horrified was that the air in the carriage was decreasing, and some people had symptoms of breathing difficulties.

And she saw that some passengers were already confessing their funeral to their families. She herself sent a message to her mother, saying that she was going to die, and she was a little scared.

According to the videos and pictures sent by netizens to the author, whether it is a carriage or a tunnel, you can see the yellow water on the waist everywhere. In the subway tunnel, some passengers supported the sides of the tunnel and slowly moved forward under the command of the staff. In places where there is no stagnant water on the platform, passengers who are out of danger encourage and comfort each other.

After being rescued, according to CCTV footage, Mr. Zhang, who was trapped shirtless, told the camera that he was shirtless because he wanted to swim out at the time, so he took off his shirt, but due to the resistance of the water, the momentum was great. , Making it difficult for him to support, and his arm was scratched by debris in the water, and he wanted to give up for a while.

“When I saw the fire officers and soldiers coming, I felt more at ease.” Mr. Zhang said.

By eight o’clock that evening, the trapped passengers were rescued one after another, but 12 passengers were still killed. At noon on July 21, the official website of Zhengzhou Metro also adjusted the color to black and white.

How to pour flood water into Zhengzhou Metro?

“Rainfall breaks historical extreme value”

The location where the subway was trapped was in the tunnel between Bintansijie Station and Shakou Road Station. On this ring line subway, Rose Park Station is the starting station and the terminal station, and Bintang Temple Station and Shakou Road Station are two stations next to Rose Park Station.

According to information from the “Zhengzhou Metro”, at 3:30 pm yesterday, they began to continuously release news about the temporary closure of individual stations. One hour later, the entrance and exit B of Yaozhai Station on Line 5, the entrance and exit D of the Second People’s Hospital of the city, Entrance A of Houhelu Station was temporarily closed. Since then, Fengzhuang Station, Qiliyan Station and Zhengzhou East Station on Line 5 ceased operations.

Among the stations that have ceased operation, Yaozhai Station is the closest to the tunnel where the accident occurred, with 3 subway stations separated from it.

However, for Line 5 with 32 stations, the temporary closure of 6 stations before the incident did not significantly reduce the passenger flow on this busy line. Line 5 still carries passengers through Zhengzhou City. under.

Zhengzhou Metro finally announced that the city’s railways would cease operation at 6:10 that afternoon. At that time, Zhengzhou City was in the red warning of heavy rain, and that line 5 had been trapped in the tunnel.

At 17:22 before the accident, the Central Meteorological Observatory issued a heavy message on its official Weibo: “After repeated verification by colleagues, the rainfall in Zhengzhou reached 201.9 mm from 16:00 to 17:00!” After that, Henan Province The Meteorological Observatory reposted this Weibo and wrote that “the rainfall in Zhengzhou broke the historical extreme value”.

At 17:00 that day, Zhengzhou City also upgraded the second-level emergency response for flood control to the first-level emergency response.

According to Article 32 of the “Zhengzhou Urban Rail Transit Operation Management Measures”, if natural disasters, bad weather conditions, etc. seriously affect the safety of urban rail transit operations and cannot take measures to ensure safe operation, the operating unit shall promptly provide transportation to the city. The competent administrative department reports, and may suspend line operation or part of the road section operation.

How to pour flood water into Zhengzhou Metro?

Insufficient drainage capacity of municipal pipe network

In May 2019, Zhengzhou City Administration issued the “Emergency Plan for Urban Flood Control in Zhengzhou”. According to the plan, as of that time, the flood control standard of Zhengzhou urban area and surrounding rivers had reached the once-in-50-year flood control standard, and the drainage standard of some rivers in the urban area had not reached the once-in-five-year flood control standard.

“Through the investigation of the drainage problems in Erqi District, Jinshui District, Guancheng Hui District, etc. in Zhengzhou City in recent years, it is found that due to the increase in urban area and changes in the underlying surface of the urban area, the drainage capacity of the originally planned and designed pipeline network is insufficient. .” wrote in the plan.

The beach temple station and Shakou road station in the accident are located in the Jinshui area where the drainage capacity of the pipe network is insufficient.

Chen Jian, Guangzhou Metro Design and Research Institute once published a paper entitled “Analysis of the Causes and Policies of Flood Disasters in Subway Stations”. When analyzing the external macro causes of subway floods, he said that urban construction caused the original underlying surface. The form has changed, the infiltration of surface water has drastically reduced to almost zero, and almost all precipitation depends on the municipal drainage pipe network.

According to the “Released by Zhengzhou”, at the time of the incident, the continuous heavy rain caused serious water accumulation in the Wulongkou stop of Line 5 and the surrounding area. At 18:00 that day, the accumulated water broke down the water retaining wall of the subway station’s entry and exit line. Positive line interval.

Chen Jian wrote in the paper that the subway should do a good job of “blocking” in the early stage when designing the “flood protection project”. For example, the ground drainage around the entrance and the wind pavilion should be coordinated with the surrounding roads, slope protection and other facilities to form a complete synergy. The drainage system of the station; anti-flooding gate grooves are set up as flood-proof panels; anti-flooding gates are installed in the station.

In terms of drainage design, Chen Jian wrote that when the artesian flow cannot drain the water on the walking surface in time, consider setting up a reservoir for regulation and storage, but the reservoir must be able to be gravity connected to the municipal drainage network to drain. If gravity cannot be discharged into the municipal pipe network, a drainage pump needs to be installed for active drainage, but the pump house will increase the construction and operating costs of the subway project.

Once the rainwater enters the station, it must first be discharged with a sump submersible sewage pump, but the final destination of the forced discharge is still the municipal drainage network. “When the municipal pipe network is fully loaded, even if the amount of water discharged to the ground is large, it will still be poured back into the station.”

Chen Jian believes that in the underground part of subway projects, flood prevention and drainage are mainly based on prevention, and the systemic measures of prevention and blockage of civil engineering are used to avoid water ingress accidents.

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