Will the vibration butterfly effect of Beijing subway affect precision instruments?

The train of Beijing Metro Line 4 whizzed past 13.5 meters underground. In the eecs building at a distance of 100 meters, it is "like a hurricane" under the electron microscope.

With the naked eye, this 1 meter-high white metal lens barrel stands firmly on the table. When it is adjusted to the highest accuracy, it will be found that there is a "burr" in the black and white image on the display screen, and the original atomic pattern becomes blurred due to vibration.

On the campus of Peking University, the precision instruments affected by subway operation are far more than this million-dollar electron microscope. When Line 4 was opened, Peking University had precision instruments worth 1 1 billion yuan, of which 400 million yuan was affected.

In order to reduce the interference of subway vibration on these instruments, Beijing and Peking University have made great efforts. In the east gate section of Peking University on Line 4, the subway company laid the most advanced vibration reduction track. Peking University has specially built a comprehensive scientific research building in a distant place and transferred some precision instruments, but the influence of subway vibration is still difficult to eliminate. Some scholars can only do experiments in the middle of the night after the subway stops.

In 20 19, the second phase of the subway 16 line, which is 600 meters away from the comprehensive research building, will be opened, and the precision instruments of Peking University will face the dilemma of being attacked from both sides. Zhang Zhiqiang, director of the Environmental Protection Office of Peking University Laboratory and Equipment Management Department, believes that the situation is not optimistic unless more vibration reduction measures are taken.

Peking University is not the only scientific research institution facing subway vibration interference. The reporter learned that Tsinghua University, Chinese Academy of Sciences, Fudan University, Nanjing University, Capital Medical University and Zhengzhou University School of Medicine had encountered similar difficulties. Subway will be built around the University of Science and Technology of China, Zhejiang University and Nantong University.

The increasingly dense subway network in cities and the increasingly sensitive precision instruments of scientific research institutions are all signs of the rapid economic and social development in China. But when high-tech instruments meet subway lines, who should avoid them becomes an irreconcilable contradiction.

Beijing subway network in 2020 after planning.

Butterfly effect of subway vibration

The subway tracks in Beijing are developing rapidly. By 2020, their total mileage will be close to 1000 kilometers. There will be nearly a thousand trains speeding on the track at the same time during the rush hour.

These trains, which weigh more than 100 tons, have become a huge vibration source while carrying passengers. Vibration spreads to the surface like ripples through steel wheels, rails, tunnels and soil, and enters buildings.

Few people pay attention to the impact of this vibration on the city. The Laboratory of Track Vibration Reduction and Control of Beijing Jiaotong University is an early research team in China. The data they tested showed that in the past 10 years, the ground micro-vibration within the distance of Beijing from the subway 100 meters increased by nearly 10 times.

Although the micro-vibration caused by traffic is not strong, it lasts for a long time and its influence is hidden, so it is not easy to be found. It once caused cracks in an ancient church in the Czech Republic and then collapsed, which affected the performance effect of the Bastille Opera House for a long time and interfered with Intel's carving of nano-scale circuits on integrated circuit boards.

In subway vibration, the most serious interference to precision instruments is low-frequency vibration. This vibration has a long wavelength and is not easily attenuated in soil. Lei Jun, director of Peking University Environmental Vibration Monitoring and Evaluation Laboratory, once measured several subway lines in Beijing with students carrying seismographs. They found that in the low frequency range where precision instruments are more sensitive, the ground vibration intensity at a distance of 0/00 meters from the subway/kloc is 30 ~ 100 times higher than when there is no train passing by.

For the precision instruments in Tsinghua of Peking University, the subway almost means a "disastrous blow".

Before the opening of the subway, in these two most famous universities in China, the environmental vibration caused by buses and railways has approached or even exceeded the safety values stipulated by some instruments. However, most of these instruments have surplus when formulating the vibration requirements of normal use environment, so they can still work normally. Once the nearby subway line is opened, the precision instruments sensitive to vibration in the two universities may not work normally with the highest accuracy.

Some scholars believe that this has caused great waste. "Instruments that cost 1 10,000 dollars can only cost 1 10,000 dollars".

Many instrument users don't know that subway vibration will affect the instrument. A colleague once found Lei Jun and complained that a precision instrument for measuring the age of rocks in the laboratory suddenly appeared abnormal. The teacher called the manufacturer and the left and right sides were adjusted. Even if it can't be repaired, the manufacturer is puzzled.

Lei Jun asked: "When did it start to be abnormal?" The other party said, "Since 2009." In fact, it is not that the instrument is broken, but that the vibration interfered with the instrument after the opening of Metro Line 4.

"There are less than 100 experts studying subway vibration in China, including equipment manufacturers." Ma Meng, an associate professor at Beijing Jiaotong University, thinks that this is a very small academic circle, and most experts are still in the same WeChat group.

10 For many years, Lei Jun has been calling for attention to subway vibration on various occasions. As a member of the Jiu San Society, he wrote many proposals, hoping to reflect this problem to the National People's Congress. Whenever there is an opportunity, he teaches unknown scholars and students about the influence of subway vibration.

For a long time, he was originally engaged in seismology and devoted himself to this unpopular academic field. His family often advised him not to "do nothing".

In Lei Jun's view, this field is quite important. He knocked on the table and asked, "China is undergoing industrial transformation, but why have our scientific and technological achievements been so great in recent years?" ? Some core electronic components, including chips, mask aligner, grating thin materials and many other fields are processed. Why can't you make the same thing even if you buy back a whole set of foreign production lines? A big reason is that the environmental vibration exceeds the standard. Today, we have been able to produce rough industrial products. Our shortcomings are mainly in accuracy, but we can't be too small. "

He has done environmental vibration assessment for two units. One is China Institute of Metrology, which is the highest metrological research center in China. The environmental vibration of the original site exceeded the standard seriously, and then it was moved to Changping. However, the evaluation found that there are still some problems in the new website. The other is the national defense metering station, and the environmental vibration exceeds the standard 100 times.

For experts who specialize in environmental vibration, the micro-vibration caused by subway looks like a butterfly flapping its wings, but in the high-tech field sensitive to vibration, it is enough to cause a disastrous storm, thus restricting the development of a country: mask aligner needs to draw thousands of lines within the range of 1 mm, and the external environment needs to be extremely stable; The high-speed rotating gyroscope in missile system must ensure that the center of mass and geometric center are completely coincident when machining, otherwise it will point to the east and west.

On the map, Peking University campus is adjacent to the subway line.

A lose-lose compromise

Like many outside scholars, Lei Jun didn't know that subway vibration had an impact on precision instruments. In China, the fierce struggle between Peking University and the subway made this problem surface for the first time.

In 2003, the planning of Beijing Metro Line 4 was announced and will be posted in the "Southbound Journey" at the East Gate of Peking University. Several universities of science and engineering and many important laboratories of Peking University are closely distributed on both sides of the subway line, and a considerable number of precision instruments of Peking University are concentrated in these scientific research buildings. Some scholars reminded Peking University that it is necessary to study whether the subway has an impact on precision instruments.

Before Lei Jun studied the earthquake resistance of buildings, all of them were large-scale vibration, and little attention was paid to the influence of micro-vibration. After collecting the vibration data of other subway lines in Beijing, he found that "this problem is very complicated and much more severe than expected".

Because of the report of him and his colleagues, Peking University opposed the passage of Line 4. At that time, Peking University and the subway company repeatedly debated two plans: either Peking University moved out completely or Metro Line 4 was rerouted.

Until the last seminar, the two sides were still deadlocked. The meeting was presided over by a deputy mayor of Beijing, and invited an academician and many experts from outside Peking University.

Academician said at the meeting that the track vibration isolation scheme is feasible. He took his own plan as an example. "Touch it with your hands and you won't feel the vibration."

A representative of Peking University asked on the spot: "How sensitive is this sensor of human hands?" The electron microscope, which is the most sensitive to vibration in Peking University, is hundreds of times more sensitive than the human body.

At the meeting, a resolution was finally reached and a compromise plan was adopted-Line 4 will cross the 789-meter track section of Peking University, and the world's most advanced track vibration reduction technology will be adopted, that is, steel spring floating plates will be laid under the tracks. This kind of floating board was invented by a German company. It consists of a reinforced concrete slab with a thickness of about 50 cm and a steel spring supported below, which can isolate the vibration of the train from the ballast bed.

"For the train, this is equivalent to a very soft cushion, and the spring separates the vibration." Ma Meng, an associate professor at Beijing Jiaotong University, said in an interview with China Youth Daily? Zhongqing online reporter, this kind of track vibration reduction technology has reached the limit to a certain extent. If it is softer, the safety of train operation may not be guaranteed.

Generally speaking, this kind of floating plate can isolate vibration well, but it also has a big disadvantage: due to the principle of vibration isolation, it is useless for vibration below the natural frequency, and may even be amplified.

In 2009, after the opening of Peking University East Gate of Line 4, Ma Meng and his colleagues made another test to verify this theory. In Ma Meng's view, this kind of track vibration reduction measure is still useful, which ensures that many instruments with low requirements can be used normally, but for some extremely sensitive equipment, it will aggravate the interference.

Peking University is not satisfied with this result. Through observation, it is found that the vibration intensity of the former site of the school hospital in the southwest is slightly smaller. Peking University decided to build a comprehensive scientific research building in this area and remove some affected instruments. However, due to limited space and funds, only about one-third of the equipment can be stationed.

20 1 1 when the foundation of the building was laid and the lower floor was under construction, news came that the subway 16 line would bypass the west gate of Peking University, only 200 meters away from the comprehensive research building.

Because the school's precision instruments have nowhere to move, Peking University strongly protested. Lei Jun analyzed that this embarrassing situation occurred because the subway company thought that the vibration reduction was successful and did not know that Peking University was planning to move the instrument. At the same time, they did not inform Peking University of the planning plan in advance.

Beijing allocated tens of millions of special funds, and a key project team was formed by the Municipal General Institute, Beijing Jiaotong University, China Electronic Engineering Design and Research Institute, china academy of railway sciences and Peking University, and came up with a set of comprehensive solutions, including redesigning the comprehensive scientific research building, considering installing a vibration reduction platform on the lower floor and suspending the whole building with springs.

Lei Jun remembers that in those months, there were two or three days of meetings every week to discuss, and several parties often fought for specific plans. An expert from the Electronic Design Institute told the reporter that Peking University's requirements were too idealistic, and the data collection and analysis methods of both sides were different, which led to several times of differences.

Some experts have heard a joke: if this matter is not handled well, it will affect Peking University's "impact on the Nobel Prize".

Just as the two sides were arguing, the project suddenly stopped. It is said that the leaders of Peking University and a city met at a meeting and the two sides shook hands. 16 subway takes a step back and detours more than 300 meters to the west, getting rid of two stops, and Peking University no longer wants it.

Yang Yiqian, a researcher in china academy of railway sciences, is one of the experts in the project team. In his view, in this game, Peking University seems to have won, but it is not. This is not a perfect solution, it is just a "lose-lose compromise".

Missing environmental standards

Yang Yiqian believes that taking a step back from the subway can reduce the interference with Peking University's precision instruments, but this distance is often not enough to eliminate the impact. On the other hand, after the subway was rerouted, it lost its function of attracting passengers.

At that time, he suggested that Peking University move the precision instrument building to the suburbs, thus completely eliminating the interference. But for many Peking University teachers, such suggestions are hard to accept. Yang Yiqian can understand that after all, Peking University was founded first, and the subway is behind, and no one wants to move.

Both he and Lei Jun agree that to avoid such contradictions and conflicts, we should pay attention to coming first and then arriving in planning. Newly planned subway lines should avoid high-tech zones sensitive to vibration as much as possible, and new high-tech zones should be selected in suburbs without subways as much as possible.

At present, the crux of the problem lies in the fact that the precision instruments of scientific research institutions are often purchased first, but the relevant influence is not considered when the subway planning scheme is formed.

Yang Yiqian is familiar with foreign laws, regulations and standards. Japan has a special vibration method. Vibration sensitive equipment is involved in the environmental impact assessment standard of American rail transit.

These two countries have also learned their lessons. The University of Tokyo used to suspend a whole building with springs, but it still could not eliminate the vibration. Because the light rail passed through the campus, the University of Washington, USA, took the track vibration reduction measures to reduce the speed, but there were still five buildings in the 15 sensitive building with excessive vibration.

"Vibration reduction is a world problem, and the best way at present is to avoid it." Lei Jun often cites Tsukuba Science City in Japan as an example. This city with Japanese scientific research talents was founded in 1963, and it was not until more than 40 years later that the subway was connected, 2.5 kilometers away from the urban area.

There is no law on the prevention and control of environmental vibration pollution in China. Although there are provisions in environmental protection standards on the impact of vibration on people in residential buildings, office buildings, hospitals and schools, there is no interference with precision instruments. As a result, the subway planning scheme entered the EIA stage, and the environmental protection department rarely considered this aspect.

Recently, the Ministry of Ecology and Environment issued the Technical Guidelines for Environmental Impact Assessment of Urban Rail Transit (Draft for Comment), but the impact of vibration on vibration-sensitive instruments has not been mentioned.

Yang Yiqian also found that even environmental protection practitioners have different attitudes towards this issue. Some people think that this problem naturally belongs to the environmental protection department, while others firmly believe that it will not return.

The lack of relevant evaluation standards has led to many subway schemes being thoughtless when passing through scientific research institutions and industrial parks. When planning a subway in a provincial capital city, a subway station was specially set up in a hospital affiliated to a university in order to facilitate patients' travel. Unexpectedly, some medical equipment can't be used normally.

When potential problems are discovered, it is often too late. Once the specific subway plan is approved layer by layer, "100 meters is almost impossible to move out".

This often leads to the confrontation between universities and subways. The 15 line was originally planned to pass through Tsinghua University, which was strongly opposed by Tsinghua. In the end, Line 15 only entered120m in Tsinghua, and did not connect with Line 4, forming a transfer station.

As early as 1955, there was a railway change in Tsinghua University. Jing-Zhang Railway is located on the same side of Tsinghua campus, and its vibration seriously interferes with scientific research. Thanks to Tsinghua's efforts, the railway line moved 800 meters eastward.

Not all universities have strong negotiation ability. 985 colleges and universities directly stamped the consent documents without much consideration. Some colleges and universities are losing money and unwilling to go public.

When the subway scheme has become a reality, other vibration reduction measures can only be taken. China Electronic Engineering Design Institute Co., Ltd. has made a vibration reduction plan for Fudan University, Nanjing University and other universities affected by the subway.

Zuo, an engineer of the Vibration Technology Research Center, told the reporter that the best solution at present is comprehensive vibration reduction, except for laying steel spring floating plates under the track and installing spring-supported vibration isolation brackets at the beginning of the construction of the instrument building. If the building has been completed, only one damping platform can be installed under each instrument, and the cost will be greatly increased.

After the opening of the 16 line, Peking University can only adopt the second scheme. Zhang Zhiqiang, director of the Environmental Protection Office of Peking University Laboratory and Equipment Management Department, estimated that a state-of-the-art air spring shock absorber needs about one or two million yuan, while the instruments needed for vibration reduction in Peking University are "in the order of tens or hundreds".

Witnessed the advanced German floating board, complicated building renovation and relocation, and expensive subway rerouting, Peking University's most advanced electron microscope will be equipped with a complex vibration reduction platform in the future. But no one can guarantee whether it can escape the interference of subway vibration.

The above content comes from: Shangguan