Qinghai-Tibet Plateau is the largest permafrost region in China. Frozen soil is extremely sensitive to temperature and has great influence on railway construction. In the frozen state, frozen soil, like ice, expands with the decrease of temperature and is built on the road above.
The foundation and track will be hoisted by it. In summer, the melting volume of frozen soil is reduced, and the railway tracks are also lowered. Repeated freezing and thawing of frozen soil will cause serious deformation of subgrade, and the whole rail will be uneven or even twisted into a twist shape, which will affect normal traffic.
Building railways in permafrost regions is a worldwide engineering problem, which has not been well solved. Railways have been built in permafrost regions all over the world for more than 100 years, but the disease rate of railways in permafrost regions has been very high, and the train speed is only 60 to 70 kilometers per hour. Trans-siberian railway, the first Russian railway with a history of one hundred years, suffered from a wide range of diseases, such as melting, sinking, frost heaving and so on. The disease rate of the line surveyed in 1996 reached 45%. Trans-siberian railway 1994, the second line built in 1970s, has a line disease rate of 27.5%. The speed of frozen soil railways in the United States, Canada and other countries is also not high.
As far as alpine permafrost is concerned, the frozen soil railway in Siberia, Russia is longer than ours, with three or four thousand kilometers, but the altitude is not high, only two or three kilometers. Although Canada, the United States and other countries also have frozen soil, it belongs to high-latitude frozen soil and is relatively stable. Qinghai-Tibet Plateau is the region with the highest altitude and the largest frozen soil area in the middle and low latitudes in the world. In addition, the Qinghai-Tibet Plateau is young and has frequent tectonic movements. The frozen soil here has the characteristics of high ground temperature, thin thickness and extremely unstable, and its complexity and uniqueness are unparalleled in the world. The Qinghai-Tibet Railway passes through the most developed frozen soil area.
Second, how to solve the frozen soil problem?
The design principle of "active cooling, foundation cooling and frozen soil protection" is adopted for the first time in the construction of Qinghai-Tibet Railway, which is a revolution for "passive thermal insulation". In the design, try to avoid the section where the phenomenon of bad frozen soil develops, and adopt the method of "crossing the bridge" when encountering the thick underground frozen soil section with extremely unstable high temperature. Various measures were taken in the construction, such as flaky ventilation subgrade, flaky ventilation berm, ventilation pipe subgrade, hot rod, laying insulation board and so on. To improve the stability of frozen soil subgrade, many frozen soil engineering measures are the first at home and abroad. There is a special subgrade on the Qinghai-Tibet Railway, that is, rubble with a certain thickness is filled at the bottom of the earth embankment, and then a subgrade with soil layer is laid on it. This 1 1 1 km "gravel layer ventilation subgrade" is the first case in China. It is like a cooling fan, which takes away the heat of subgrade and foundation in winter, absorbs less heat in summer, plays a role in cooling down, and can effectively protect the stability of frozen soil subgrade.
Professor Zhang, the head of the expert group on Qinghai-Tibet Railway construction and an expert on frozen soil, believes that the possibility of large-scale frozen soil engineering diseases on Qinghai-Tibet Railway is relatively small, and the train speed can reach 100 km or more, so it is no problem to keep it open all the year round.
Third, how to ensure the personal safety of builders?
The average annual temperature along the Qinghai-Tibet Railway is below zero degrees Celsius, and the oxygen content in the air in most areas is only about half that in the mainland. Cold and lack of oxygen, sandstorms raging, strong ultraviolet rays and numerous natural foci are called the "forbidden zone" of human survival limit. How to ensure the life safety of builders in harsh environment is also a worldwide problem.
The Ministry of Railways and the Ministry of Health have formulated perfect health protection measures, so that the ratio of medical personnel to construction personnel reaches 1.5%-2%. The whole line is equipped with more than 3,900 sets of conventional medical equipment, and employees are sent to the on-site hospital for effective treatment within half an hour. Following the physiological law of plateau, all contractors are allowed to enter the construction site after a week of "adapting to the environment" in lower altitude areas. Limit the working hours of personnel and adopt mechanized construction to reduce labor intensity. In order to prevent hypoxia at high altitude, the construction unit creatively used hyperbaric oxygen chamber at an altitude of 4,500 meters to 5 100 meters, which filled the medical gap at home and abroad. It is the first time in the world to carry out scientific research on artificial oxygen production at high altitude. In Huo Feng Tunnel at an altitude of 4,905 meters, a plateau medical oxygen-making equipment was developed to produce 24 cubic meters of high-purity oxygen per hour, and this technology was summarized and popularized. A 17 large-scale oxygen station was built along the whole line, which effectively improved the working environment. Fourth, how to protect wild animals?
In order to protect the unique and extremely precious wildlife resources on the Qinghai-Tibet Plateau, the railway route selection should try to avoid the key areas where wildlife inhabits and moves, and the Tibet section of the project bypasses Pengbo Black-necked Crane Reserve in Linzhou City. For the road section that must pass through the wildlife activity area, organize experts to study the protection of wildlife, master the distribution habits and migration laws of wildlife along the line, and minimize the interference to them. There are 33 wildlife passages along the Qinghai-Tibet Railway, with a cumulative width of nearly 60 kilometers. According to the migration habits of different animals, the passage is designed in three forms: under the bridge, above the tunnel and at the gentle slope.
5. How to protect the plateau vegetation?
Builders adopt the method of subsection construction and vegetation transplantation. First, cut the turf in the construction area into pieces, and then transport the turf together with the soil to the turf transplant area with a forklift, and a special person is responsible for maintenance. After the subgrade is formed, the turf is transplanted back to the subgrade slope. For areas with good natural conditions south of Kunlun Mountain, grass species suitable for plateau growth should be carefully selected, supplemented by suitable technologies such as spray sowing and plastic film mulching, so as to restore surface vegetation as much as possible. Turf planting and transplanting experiments were carried out in high altitude areas such as Tuotuo River, Amdo and Dangxiong. After success, it was popularized in the whole line, which set a precedent for the successful experiment of artificial grass planting in the alpine region of the plateau in the world.
In order to protect plateau wetlands, the Qinghai-Tibet Railway should avoid wetlands as much as possible. When it is necessary to cross the wetland, measures such as "replacing the road with a bridge", setting more culverts and filling stones at the subgrade base are generally taken to prevent the underground runoff of the subgrade from being cut and the wetland from shrinking.