Elevated railways facilitate bullet train journeys in China
- By Wu Jin
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E-mail China.org.cn, November 15, 2017
Sharp-eyed passengers may have been astute enough to note the bullet trains in which they are traveling are usually running on elevated tracks. That naturally raises the question: Why can't the railways be laid entirely on the ground?
The answer can be found in the nature of the high-speed railways themselves, reported the Paper, the country's emerging online media outlet.
A high-speed railway has to be straight and smooth
Due to the high operating speeds, the railways have to be built in straight lines and must avoid sharp turns by extremely large and gentle curves. Usually the semi-diameter curve of such a railway where trains are running at a speed of 350 kilometers per hour should be no less than 7,000 meters.
The construction of elevated tracks will greatly reduce the difficulties caused by crooked routes that might otherwise be hard to avoid if laying the railway ties on the ground and having to follow its contours.
Smoothness means to build the railway with few undulating slopes that may affect the operation of the high-speed trains.
Avoiding subsidence
The conventional construction of railways involves the filling of clay and stones to provide the foundations, which need to be compacted because of their loosening tendencies. However, no matter how hard they are consolidated at the start, the surface will subside at some point.
Moreover, if the railway is laid on a soft roadbed, the soil is prone to subsidence under the weight and vibration.
However, the problem is dealt with through foundation piles that can extend to the rock strata underground to support the railways. Their depth, up to 60 to 70 meters, varies with different underground rock compositions in a bid to avoid subsidence.
Economical use of land resources
The economical use of land resources can be exemplified by the construction of the high-speed railway between Beijing and Shanghai, comprising elevated sections totaling 80 percent of the entire length and saving a land area of 30,000 mu (about 20 million square meters).
Although the cost of elevated lines is high, they become less expensive if comparing to the reimbursements necessary for land acquisition.
Other reasons
Elevated railways can also lower maintenance costs, increase safety, reduce management risks and remove troublesome pedestrian and vehicular flows at traditional level crossings.
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