Xiao Wang is curious about the subway construction process
This summer, college student Xiao Wang passed by a subway site under construction. Seeing the huge excavators running underground, creaking and creaking regularly, he couldn't help but imagine what was happening underground.
Xiao Wang knew that to build a subway tunnel underground, he had to dig up a lot of earthwork first. But he had never seen a cart carrying bare dirt, which puzzled him.
So, he decided to get to the bottom of it and investigate the flow of these earthworks.
Back home, Xiao Wang first searched for information about subway construction on the Internet. It turned out that this huge system could be constructed by two main methods, namely the cut-and-cover method and the drill-and-dig method.
Although the former is simple to operate, it requires complete destruction of surface buildings, which has too much impact on urban development; The latter can retain the surface to the greatest extent, but there are many engineering and technical problems.
It seems that the problem is not simple, Xiao Wang can't help but sigh in his heart, he still needs more data and cases to support his reasoning. So, he decided to go to the library tomorrow to find more relevant books to read and analyze the advantages and disadvantages of these two construction methods for himself.
Comparison of the open-cut method and the drilling method
Early the next morning, Xiao Wang came to the city library and read professional books on subway construction in the construction engineering area. It is mentioned that the cut-and-cover method is the most traditional construction method, which requires the excavation of a narrow foundation channel directly on the surface, but this is bound to destroy all the buildings on the surface, and the impact on traffic and the living environment of residents is extremely bad.
In contrast, the drilling method is more advanced and applicable in many ways. In this method, multiple shafts are set up along a predetermined route, which can be accessed directly from the ground for tunneling and excavation work, while preserving the surface state to the greatest extent.
But because of this, the difficulty of construction supervision and operation will be greatly increased, and the equipment accuracy and personnel skills will be required higher.
Xiao Wang was full of emotion, it turned out that these two methods have their own advantages and disadvantages. In terms of earthwork treatment alone, the open-cut method is undoubtedly the easiest to excavate and transport directly on the ground, but it has great damage to the surrounding environment; The excavation method is extremely complex to transport and handle the earthwork in the narrow and enclosed space of the tunnel, but it has no effect on the surface.
It also made him wonder why it was rare to see large-scale bare earthwork transportation scenes.
Efficient operation of modern EPBs
Looking through more and more data, Xiao Wang gradually has a new understanding of modern subway construction technology. It turns out that at present, China's subway construction has widely used high-tech equipment - tunnel shield machine, which is a modern exploration equipment integrating multiple functions of tunneling, support and transportation.
It operates efficiently in tunnels, with powerful speed gears and hydraulic ejector rods to continuously cut and crush soil and rock. This makes it possible to continuously excavate automatically, more than several times faster than manual excavation.
At the same time, a large amount of excavated debris is immediately transported to the crushing system inside the shield machine, where it is processed into a homogeneous slurry using pumps and agitation, and then pumped to the ground for sorting through a built-in spiral conveyor belt tens of meters long.
This system is ingenious and tightly sealed, completely eliminating the leakage and pollution of the external environment. At the same time, the TBM can adjust the direction and speed in real time according to the excavation situation, ensuring that the tunnel runs through the planned route without errors.
Analysis of the challenges faced by subway construction
Although modern technology has greatly promoted the subway construction process, Xiao Wang understands that there are still huge challenges to achieve the normal operation of a subway system. The first is the astronomical upfront construction cost.
Every kilometer of tunnel excavation and underground site construction will cost hundreds of millions of yuan. This has strained the financial resources of many small and medium-sized city governments.
Even more severe are the long-term losses in the operational phase. According to statistics, only 7 cities are currently profitable. The cost of manpower, electricity and other costs spent on the daily operation of other cities seriously exceeds the ticket revenue.
This is mainly due to the fact that except for the morning and evening rush hours, the subway passenger flow is low during the rest of the time, which is difficult to meet the huge cost of system operation.
In order to turn losses into profits, subway operations also need to be combined with buses, taxis and other multimodal transportation. This not only alleviates the peak pressure, but also increases the daily number of visitors to the subway and increases the operational efficiency.
Of course, this also requires the government and enterprises to jointly invest resources and energy, and provide more humane and thoughtful services for the people.
Conclusions and expectations
After days of research, Xiao Wang finally figured out the whole process of subway construction. He understands that it is not only the cold machinery that is running behind it, but also the hope of urban development.
Despite the difficulties, the joint efforts of the government and professional teams can make great progress as the main force of urban transportation.
This can't help but Xiao Wang is full of good expectations for the future of subway construction. Perhaps one day in the future, large, medium and small cities will have convenient and comfortable subway systems, and people will travel faster and more efficiently.
At that time, Xiao Wang will definitely take the initial curiosity and step on the subway tunnel again to take a look at them one by one, and feel the changes brought about by scientific and technological progress.
At the same time, he will always pay attention to and support the efforts of the subway builders.