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Have you ever sighed at the bustling city of the city when you looked out the window at the rapidly receding tunnel wall when you took the subway? The train runs in a tunnel dozens of meters underground, as if you are in another world.
Looking to the future, the times are moving forward with a majestic momentum, and the subway has undoubtedly become an indispensable and important part of the urban transportation system.
The subway train runs through the glittering underground tunnels like the wind, running through the pulse of the bustling city. Once a barren place, it is now the main artery of urban life.
However, as the construction of the subway is in full swing, we have to face a serious question that needs to be answered: when the underground tunnels are built, a huge amount of waste earth will inevitably be generated, but what will happen to the soil? Workers sweat and rain and dig up tons of soil from the bottom of the earth with shovels and machines.
According to relevant data, nearly 110,000 cubic meters of waste soil will be generated for every kilometer of new underground tunnels alone. Perhaps these numbers may not be intuitive to most people, but let's take a simple example: if all the waste soil from the construction of a subway tunnel in Shenzhen was dumped into Hangzhou's West Lake area, it would be almost enough to turn the surface of the lake into a flat land.
The beautiful scenery of the ten scenic spots of West Lake will no longer exist, and the lake will be covered with a large amount of loess, and the scene is extremely terrifying.
So, why don't we seem to see mountains of waste dirt on the construction site in our daily lives? In fact, the answer still has to go back to the specific methods of subway station construction.
The usual first approach is to trace the excavation from the ground down until the desired depth and length is reached, then backfill the soil on top and rebuild the ground on top of it.
This practice, known as the "open cut method", is a process in which workers act like a group of tiny soil slabs, digging large pits one pit after another in the urban surface, and then backfilling the soil when the tunnel is completed.
Because this method has a huge amount of engineering and a vast excavation area, it has more significant but relatively limited limitations, such as during the construction operation, the ground building shall not carry out any activities without authorization, for fear of causing the building to tilt and sink.
Therefore, this method is mainly suitable for the development and construction of new towns, where there are not many buildings on the ground.
In the old cities, the use of open-cut excavation is too risky because the ground is already covered with high-rise buildings, so the second method called "drilling method" is still the most frequently used in practice.
The drilling method starts with the excavation of a vertical shaft with the upper depth of the tunnel at the same depth as the shaft, followed by the underground operation from the shaft and the gradual development and excavation of the tunnel.
In order to shorten the construction period, engineers will speed up the construction of the tunnel by setting up multiple shafts in parallel and working together with multiple teams of workers at the same time.
Compared with the cut-and-cover method, the drilling method is not limited by the constraints of the above-ground building, so the construction in the urban underground space does not need to be concerned about the surrounding environment. This is undoubtedly good news for those old cities with a long history and cultural heritage, which can protect the city's appearance to the greatest extent.
More importantly, the use of drilling and excavation can break through the depth limit of the open cut method, so that the subway tunnel can go deeper underground and obtain greater "value" significance, for example, in specific cases, the subway tunnel can be used as a secret material delivery channel or the use of an air-raid shelter, fully demonstrating its advantages of cycling to protect the tiger from danger and avoid danger.
Truth be told, however, the drilling method is not without its merits. Since each excavation operation is carried out independently, the underground workers cannot directly observe the direction of the track path, so that sometimes the excavation process will deviate from the established direction, which will bring a lot of trouble to the subsequent project.
It has its own unique problems, such as the fact that the only vertical wellhead is the exit, so it is not easy to transport a large amount of earth and rock from the construction out of the hole, and the workers have to shuttle back and forth like ants.
However, if you want to dig deeper into the root causes, it is still very positive. This giant machine seems to have infinite power, and when working underground, it is like a mechanical beast and extremely ferocious.
Although it is equipped with an incredibly sharp blade in front of it, it rotates like a huge fan, clearing the way forward. The workers looked from afar and saw bursts of yellow dust rolling in front of the shield machine, like a pioneer.
Thanks to its powerful capabilities, the EPB can excavate tunnels of more than three meters in just one hour, which is impressively efficient.
In addition, in order to ensure the stability of the tunnel, the rear of the shield machine is even equipped with important equipment for waterproofing and anti-collapse to ensure the personal safety of the workers. Of course, as a "big belly" reinforced concrete storage room inside the body of the shield machine, the amount of soil it carries is staggering.
It turns out that most of the soil resources are self-depleted, and about one-third of the soil will be used to build subway tunnels as the main source of raw materials.
When a certain amount of soil is stored in the belly of the TBM, it is automatically transported out via a conveyor belt, and the soil mixed with dirt, gravel from broken rocks, and waste soil is often used for a variety of purposes.
Workers are busy working underground, digging new tunnels and dealing with a steady stream of dirt on conveyor belts. For them, this soil is a valuable resource.
They use a screening device to sort out the grit and carefully sort it for storage so that it can be used in the next construction process.
Some workers hold shovels and mix the gravel and cement concrete evenly in proportion, stir it into a viscous mixture, and then scoop up shovel after shovel and rub it on the side wall of the tunnel.
In this way, they used their hands to make a solid concrete wall from the discarded earth excavated from the ground, thereby reducing the overall cost of building the subway tunnel, after all, such a "big project" can be called a demon that eats money.
In the case of Chinese mainland, the price of building a kilometer-long track is almost as high as 1 billion yuan, and the shield machine will consume nearly 10,000 kilowatt-hours of electricity per hour after starting, and the construction cost is staggering.
Fortunately, with recycling, the cost of subsequent maintenance is relatively small, maximizing savings.
Although a large part of the soil will be recovered by the excavation process, there is still some surplus that cannot be completely digested, so it is necessary to send earth-moving trucks to transport the inexhaustible soil to other places for use.
Heavy trucks slowly drove into the construction site, and workers rushed again, loading truckloads of dirt into truckloads.
However, why do we rarely see earth-moving trucks in our daily lives? The reason is that earth-moving trucks basically only work at night, because during the day due to the dense flow of people, moving such a large object can cause serious traffic jams.
Moreover, there are certain blind spots in such large vehicles, and driving at night is conducive to reducing accidents. Workers had to work in the dark of night to ensure the normal functioning of the city during the day.