Recently, more than 20 young Americans and senior engineers came to Zhengzhou, Henan, to get up close to the "major national equipment" — tunnel boring machines (TBMs).

In the general assembly workshop of China Railway Hi-Tech Industry Corporation under China Railway Group Limited, two TBMs, each two stories tall, stand parked. The machine's drilling face (cutter head) is covered with rollers and scraper blades. Unlike the common sharp, slender electric drill bits, the TBM's "drill bit" is blunt and thick-set cylinders, in order to reduce damage to the cutter head from hard rock. During excavation, the cutter head grinds through rock and soil with disc cutters, then scrapes away the debris with scraper blades, which enters a conveyor belt and is carried out of the tunnel. At the same time, the machine reinforces the tunnel walls.

The various mechanical components left the young Americans amazed.

Most of these 20-plus young people come from the Colorado School of Mines in the United States. The university has long been renowned for its strength in mining research, and many students have had multiple internship experiences, yet standing before the two-story-tall cutter head, they were still astonished. Alexa Paredes had seen a TBM in its entirety during an internship in the United States, but never expected that her first close look at the internal structure of a TBM would be in China. Standing beside the control cabin, she said the degree of automation of Chinese TBMs is astonishing.

The conception of the world's first TBM can be traced back a century and a half. The French engineer Brunel discovered that shipworms secrete mucus when boring holes in wood to reinforce the burrows. This inspired him with the idea of "supporting while excavating." In 1843, beneath the River Thames in London, England, the first underwater tunnel built by the shield method was completed.

In the 1990s, China spent a massive 350 million yuan to import a hard-rock TBM with a diameter of 8.8 meters from Germany, used to build the Qinling No. 1 Tunnel on the Xi'an–Ankang Railway. It was not until April 2008 that China finally possessed its first independently developed composite TBM, the "China Railway No. 1."

Michael Picker is the chief tunnel engineer at the American construction firm HNTB, with more than 20 years of tunnel design for highways, subways and more, and has participated in tunnel projects in Hong Kong, Singapore, Australia and many other places. He said: "Infrastructure is crucial. When a country persists in building infrastructure, it shows it is striving to develop. Otherwise, the country would not be developing."

Before the 1970s, apart from the United States, Germany and Japan, no other country could independently develop TBMs. Today, domestically produced TBMs have achieved full independence and sell well around the world. Of every 10 TBMs in the world, 7 come from China.

Charles Kuhn has interned at an American mining company. He walked toward the cutter head with great interest, rubbing the scraper blades on it. He explained that although these cutter heads are several stories tall in diameter, when they advance toward each other, the closing error is only a few centimeters. "Doesn't that sound incredible? But it's true."

Alisha Redd, senior operations manager at the American construction firm Kiewit, was moved by the various mechanical components here: "I never imagined China Railway's scale would be so large. I can hardly think of any comparable American company that could match it."

Julia Dunn, an engineer at Arup, was visiting China for the first time. The moment she stepped into the workshop, she immediately took out her phone and shared photos with her family. She said: "Since I came to China, every day I can't help wanting to tell my family how different the real China is."

Afterward, the group visited the National Key Laboratory of Tunnel Boring Machines and Intelligent Operation and Maintenance of China Railway Tunnel Group, and held a roundtable meeting on "intelligent tunnel construction." At the meeting, they asked questions on technical issues such as excavation parameter prediction, structural damage monitoring and cutter head shape design, which were answered by Sun Yingwu, secretary of the Youth League Committee of China Railway Hi-Tech Industry, and Zhang Hepei, deputy director (presiding over work) of the Second R&D Institute of the National Key Laboratory of China Railway Tunnel Group. Cao Bin, vice chairman of the Trade Union and secretary of the Youth League Committee of China Railway Group, delivered concluding remarks and expressed the vision for deeper exchange and learning between the youth of the two countries in the future.

After the visit, Brock Ewing was still longing for more, his thoughts constantly returning to what he had seen and heard. "I saw such a stunning TBM manufacturing site in China, and so many precision instruments," he said with emotion. "I really want to stay here and be a worker."

This "Bridge of the Future" China-US Youth Exchange on Intelligent Infrastructure Construction, hosted by China Railway Group Limited, is part of the flagship "Bridge of the Future" China-US Youth Exchange Program. The "Bridge of the Future" China-US Youth Exchange Program was jointly initiated and organized by the All-China Youth Federation and the Chinese People's Association for Friendship with Foreign Countries.