Many secret military bases in the world are built in the mountains. How do you do it by hollowing out the mountains? Did it exist in World War II? I heard that the Germans had it at home at that time.

First, make the hole

As shown in the above figure, the arch frame of the hole is set up according to the designed position, and then concrete is poured. Then it is driven into the large pipe shed, that is, the row of steel pipes above, the length of which is 1-3 meters depending on the situation. After driving, cement slurry is injected into it at high pressure. Its advantage is that the soil is bonded with the steel pipe cement slurry to form an arch-shaped reinforced soil. This way, it won't collapse easily when digging. It's probably like this after it's done:

Second, dig the tunnel body and do the first layer of support

It's time to choose different methods according to the quality of the rock, and the size and methods of digging are different. Specifically, if it is hard and complete rock, the tunnel can be dug as big as it is. If it is soil like the above picture, it will be dug in three or four pieces. This is a tunnel on the new Chengdu-Kunming line, which was dug in four parts. Now what we see is digging up left, down left, up right and down right to be dug.

Generally speaking, the rock tunnel will not collapse immediately after being dug, and the soil tunnel will not collapse immediately because of pre-grouting or anchoring (that is, coarse steel bars). At this time, the workers will put some steel arches that have been made into the outline of the tunnel in advance into the designated steel arches according to the survey instructions.

After the steel arches are put in place, the gaps between the two arches should be put with steel mesh, welded and anchored laterally. After that, concrete will be sprayed. As shown below:

After the concrete is sprayed out, it will stick to the steel frame, so that the steel frame, the rock of the tunnel and the concrete will form a whole, and * * * will bear the same force. At this time, the whole tunnel looks like this:

Of course, I found these tunnel pictures online, not the same tunnel. So I see it differently. The tunnel in the above picture is obviously excavated in two parts. Tunnels are generally supported in two layers. The first layer is like the one above. After shotcreting, it has a certain stability and will not collapse for a long time. However, if the tunnel is to be free from problems for decades, it will have to go to the next step.

Third, the second layer of support

This step is similar to our bridges and buildings, that is, reinforced concrete is used. Therefore, it is necessary to tie steel bars and lay waterproof boards inside. After all, the waterproof work of tunnels in the mountains is very important. This step is probably as shown below:

The flashing inside the dense steel bars in the above picture is called waterproof board. These steel bars are all tied and welded by workers standing on this platform. After the reinforcement is finished, the concrete is poured. Then how did the concrete get to the wall? Next, this big guy will come on stage:

This guy is called the second lining trolley, which has its own vibration function. After the previous process is completed, it will be pushed in. So there is still a gap between the whole trolley and the tunnel wall, so we seal both ends. Concrete is injected through the pipeline on the trolley body and vibrated automatically, so that the secondary support of the tunnel is made, that is, the final support. The pouring process is as follows:

After the concrete pouring is completed, the formwork can be removed after the specified curing time, and the trolley can be driven away. In the end, he became like the picture below. In this way, because it forms a closed and stable structure, it will basically not collapse like a bridge, and it is not afraid of earthquakes.

this completes the main structure of the tunnel. Followed by the tunnel pavement, waterproof and drainage, ventilation, lighting, power supply and distribution, safety and other facilities construction, here no longer repeat. The above is the most commonly used excavation process of mountain tunnels.

In World War II, Nazi Germany established a secret tunnel system in Sowie Mountain in Lower Silesia, Poland. So far, the purpose of Hitler's construction of this tunnel is still a mystery, and some people speculate that Hitler built the treasure trove.

This secret tunnel system was built in Sowie Mountain Nazi in Lower Silesia, Poland. It was a project started by Nazi Germany in 1943, when thousands of war criminals and Jews were forced to dig, including children as young as 1 years old.

Nazi Germany established this tunnel network in the context of the increasingly fierce allied operations in World War II. Some people think that Hitler built the tunnel to ensure the secret transfer of troops and military equipment by Nazi Germany, and chose this place to attack the allies more easily.

The code name of this project is "Project Riese", which means "huge" in German. There is also a speculative assumption that this work was established to connect Hitler's underground office. Because many Nazi officials mentioned this project in their memoirs after the war, saying that it was a secret headquarters for Hitler.

Another guess is that the Nazis set up this project to study and build atomic bombs.

In order to build this tunnel system, the Nazis arranged tens of thousands of prisoners in Nazi concentration camps to dig and construct it.

The working conditions of these workers are very bad, and many people died of diseases, malnutrition, fatigue or industrial accidents.

According to incomplete estimates, about 5, people died during the construction of the tunnel network.

this tunnel system is very complicated and huge. But the construction was not completed. The picture shows the reinforced concrete structure in the Osowka tunnel deep underground in the Sowie Mountains. This tunnel network spreads more than 17 meters into the mountains.

With the passage of time, experts and scientists are actively studying the secret tunnels of Nazi era, hoping to understand why Hitler built this huge project.