I heard there is a mysterious "time machine" in the tunnel? The secret behind it is...

In the evening, the gentle breeze in the Huajiao campus sways the camphor trees on both sides of the road, and also sways the curious hearts of children.

"Grandpa, can we go for a walk after dinner?" Xiao Tie swallowed the last bite of food and looked at his grandfather.

Grandpa smiled as he ate and said, "Okay, I'll take you for a walk around the school later."

After dinner, Grandpa took Xiaotie out for a walk, fanning him with a palm-leaf fan.

Grandpa walked over and said, "Xiao Tie, do you know where mom and dad work?"

"It's on the railway, rumble, rumble, the kind with tracks." Xiao Tie waved his arms to make it look like a train was moving forward.

"Hahaha, yes, did you know that there is a Huajiao person on every kilometer of railway in our country?"

Xiaotie shook his head.

Grandpa continued, "We Huajiao people were born because of the railway. Grandpa was also a railway worker who worked for decades and has a deep affection for the railway, so I suggested that your father apply to the Railway University."

( Figure 1 )

"I know! There are some photos of my grandfather working on the railway at home. I saw them last time!" Xiao Tie continued what his grandfather said.

"Xiao Tie, the railway lines of our country that stretch for more than 100,000 kilometers are built by generations of railway workers. Grandpa is retired now, and the future will be handed over to you young people to build the railway lines."

After saying that, Grandpa walked to a bench and waved to Xiaotie: "Xiaotie, come over and take a rest."

As Xiao Tie walked, he pointed at something behind his grandfather and asked in doubt, "Grandpa, look, what is that? It looks like a cannon!"

Grandpa turned around and looked at it, then smiled and said, "Oh, you mean it? That's a tunnel boring machine. Come, let me tell you about it."

Grandpa pointed underground and said, "Xiaotie, do you know what's under the city?"

Xiao Tie: "Wow, what's that? Is it treasure?"

Grandpa: "Haha, there are treasures, but most of them are things like little ants."

Xiao Tie: "Little ant? What is that?"

( Figure 2 )

Grandpa pointed at the huge machine and said, "This big machine is called a tunnel boring machine. It is like a magic shovel. It can dig out the soil from the ground little by little like digging a watermelon. It can build a tunnel like threading a needle. In this way, people can travel underground like little ants and reach their destination!"

Xiao Tie blinked his eyes and asked excitedly: "Why build so many tunnels?"

Grandpa squatted down, pointed with his fingers on the ground, and continued to explain: "Xiao Tie, tunnels are like underground roads that allow cars, trains, and even water pipes and cables to pass safely. With tunnels, people can travel more conveniently, and the buildings in the city are more beautiful!"

( Figure 3 )

【Knowledge introduction: The emergence of shield machines has greatly improved the disadvantage of traditional tunnel excavation methods that require a lot of manpower and material resources. It not only improves the efficiency of tunnel excavation, but also greatly reduces the damage to the surrounding environment. Its huge shield and advanced positioning system ensure the safety of workers and also ensure the accurate position and direction of the tunnel. When the shield machine is excavating, its shell can support the newly cut tunnel. This support function is twofold. It can not only bear the pressure of the surrounding soil, but also withstand the pressure of groundwater, laying a solid foundation for tunnel excavation, soil discharge, and lining, and improving construction stability [1]. In addition, the shield machine can also use its own cutter head to cut the soil layer and output the cut soil residue from the tunnel, greatly improving the efficiency of tunnel excavation and reducing the accident rate. 】

Xiao Tie suddenly realized and continued to ask: "Grandpa, how deep a tunnel can a shield machine dig at one time?"

Grandpa smiled, put his fist on the ground, and said, "Xiao Tie, the shield machine is like a strong warrior. It can dig a tunnel more than ten meters deep at a time and keep moving forward!"

Xiao Tie's eyes were full of curiosity: "Wow! How does it work?"

"Xiao Tie, do you know that the working principle of the shield machine is actually closely related to many things in our lives? Have you ever seen an earthworm?"

"I've seen earthworms!" Xiao Tie's voice suddenly became louder, "But earthworms are just small insects, how can they be related to shield machines?"

"When earthworms dig the soil, the muscles in their bodies contract and stretch, like this." Grandpa used one palm to gesture the way earthworms wriggle, "They keep twisting their bodies to cut and dig the soil, thus creating channels for ventilation and drainage."

( Figure 4 )

【Knowledge introduction: The shield machine is a special equipment used for underground tunnel construction. The scientific design of its machinery is crucial to ensure the smooth progress of tunnel construction. The following are some key points on the scientific design of the shield machine machinery:

1. Structural design: The structural design of the shield machine needs to take into account factors such as stress conditions, material selection, and overall stability.

2. Cutterhead design: The cutterhead is the core component of the shield machine and is directly responsible for excavating underground tunnels.

3. Earth pressure balance system design: The shield machine needs to deal with underground soil pressure during the excavation process. The design of the earth pressure balance system is crucial to balancing the soil pressure, protecting the tunnel wall and ensuring the safety of workers.

4. Guidance system design: The guidance system of the shield machine is used to ensure that the machine moves along the predetermined tunnel trajectory. The design of the guidance system needs to take into account underground obstacles, geological conditions and the stability of the machine.

"So that's it! The tunnel boring machine also works in a similar way!" Xiao Tie's doubts were solved.

"Haha, so clever." Grandpa laughed, "The cutterhead of the shield machine is like the body of an earthworm, which digs out the soil underground by constantly rotating and cutting. The propulsion system is like the muscles of the earthworm, pushing the shield machine forward while supporting and stabilizing the work of the cutterhead. This enables the shield machine to continue to advance underground, digging out one smooth tunnel after another, just like an earthworm moving through the soil, creating new underground passages."

Xiao Tie's frown, which had just relaxed, furrowed again: "Grandpa, what should we do with the soil we dug? Earthworms will eat the soil, and will the shield machine also eat the soil?"

Grandpa touched Xiao Tie's head and said, "Of course it won't eat the soil. Finally, the slag removal system of the shield machine is responsible for removing the rock and soil fragments after cutting and crushing, just like the excrement discharged by earthworms when digging the soil. The excavated soil is transported away, and the tunnel becomes very clean."

After listening to his grandfather's explanation, Xiao Tie had a wonderful scene in his mind: the shield machine was cutting the soil underground, making a low roar and the sound of the cutter disc cutting. The soil was excavated, and the tunnel was gradually revealed in front of him, extending like the blood vessels of the city. The more he thought about it, the more stunned he became, as if the shield machine in front of him had also started to work.

After a long silence, Grandpa's eyes became a little dazed. He wondered if this machine took him back to the past: "Xiao Tie, the shield machine is actually a 'time machine'."

"Time machine? Can the TBM take us to the future?"

Grandpa's tone was filled with a sense of storytelling: "Yes, when it opened the tunnel, it seemed to be digging up the memory of time. Every advance was a review of the past, opening up a new history underground. Every time it crossed, it witnessed the changes of the city. It passed through the soil and the years, leaving countless traces for the development of the city. It can take us back to the past and witness the history of urban construction."

On the grass next to the machine in front of us, there is an earthworm developing its new channel. When the soil underground is discharged to the surface, at this moment, in the eyes of the earthworm, it seems to be no different from the machine.

"Let's go, kid," Grandpa patted his trousers and stood up and said, "The story is over, it's time to go home!" The sunset glow dyed Grandpa's back. Grandpa suddenly stopped and looked back deeply at the shield machine model in front of him. The breeze brushed across their faces, bringing a hint of coolness.

"Child," Grandpa said softly, "The shield machine not only represents the development of science and technology, but also carries the spirit of railway workers. It is these unknown builders who, with their sweat and wisdom, have created tunnels connecting cities, making our transportation more convenient and efficient."

Xiao Tie listened to his grandfather's words, and a feeling of admiration welled up in his heart. He thought of his parents who worked silently to build railways and tunnels. They contributed their own strength to the infrastructure construction of the motherland with their tenacious spirit and selfless dedication. At that time, they were not only his parents, but also had a glorious title - "Chinese Railway People".

"Grandpa," Xiao Tie said with hope in his eyes, "I also want to be a railway worker like you and my parents, and contribute my own strength to the construction of the motherland."

Grandpa smiled and patted Xiaotie on the shoulder, encouraging him: "Good boy, the spirit of Chinese railway workers is to not fear hardships and difficulties, to forge ahead bravely, and to work hard for national rejuvenation. As long as you persevere and study hard, you will definitely become an excellent railway worker!"

After hearing this, Xiao Tie took two steps forward and supported his grandfather as they continued to walk back home. His heart was filled with hope and longing for the future. "Hahahahaha, kid, by then our family will be the 'third generation of Tie'!" The figures of the grandfather and grandson supporting each other gradually disappeared in the soft light of the setting sun, leaving only their hearty laughter that came with the wind...

References:

[1] Wu Yiming. Analysis on the maintenance and maintenance of shield tunnel construction machinery and equipment[J]. China Equipment Engineering, 2023(10):72-74.

Image source:

① Figure 1, Figure 3 (China Railway)

② Picture 2 (Photo taken by students)

③ Figure 4 (Chen Kunpeng, Li Jianbin, Cheng Yonglong, Tan Shunhui, Chen Shiyou, Zheng Kangtai. Shield machine for tunnel connection channel and its connection channel excavation method [P]. Henan Province: CN106437735B, 2018-06-01.)

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