A tunnel boring machine (TBM), also referred to as full-section tunnel boring machine, is a machine used to excavate tunnels. It combines multiple technologies such as machinery, electronics, information technology, and artificial intelligence, being acclaimed as the "king of construction machinery."

More than two decades ago, China did not have its own TBM. Today, Chinese-produced TBMs account for nearly 70 percent of the global market.

How did the Chinese TBMs make this giant leap? People's Daily reporters delved into the TBM manufacturing companies to uncover the secrets.

In early 2000, when China Railway Group Limited (hereafter referred to as China Railway) decided to develop its own TBM, some thought it was an unrealistic idea.

Wang Dujuan, chief engineer of China Railway Hi-Tech Industry Corporation Limited (CRHIC), a subsidiary of China Railway, said that a TBM has over 20,000 components, and its control system alone has more than 2,000 control points. "Many colleagues at that time had never even seen a TBM before," she recalled.

Thanks to substantial efforts and investments, China's first domestically developed earth pressure balance TBM with independent intellectual property rights made its debut in 2008, known as the "China Railway No. 1" TBM.

On February 6, 2009, the China Railway No. 1 TBM started working for a metro project in north China's Tianjin municipality. Four months later, a tunnel of the Tianjin Metro Line 3 was holed through, with ground settlement carefully controlled within 3 millimeters and passing all expert inspections.

Since then, the Chinese TBM industry has gained momentum, with a number of competitive manufacturers emerging and growing, such as China Railway Engineering Equipment Group Co., Ltd. (CREG), China Railway Construction Heavy Industry Corporation Limited (CRCHI), and CCCC Tianhe Mechanical Equipment Manufacturing Co., Ltd. affiliated with China Communications Construction Company Limited (CCCC).

Today, China boasts the world's largest TBM fleet, with approximately 5,000 units. Over 90 percent of China's metro tunnels were constructed using TBM technology.

A TBM stands several stories high and is as heavy as hundreds of elephants. It consists of tens of thousands of components. To enhance the resilience of the industrial and supply chains, every link of the industry must collaborate effectively.

"China's TBM industry follows a development path where the manufacturing of complete TBMs drives the manufacturing of components," said Zhang Zhiguo, general manager of CREG.

Ten years ago, bearings and gearboxes needed to be imported due to weaknesses in the industrial chain, and today, these weaknesses are gradually being resolved, Zhang told People's Daily.

Crafting main bearings proved to be one of the most challenging tasks due to the extreme and harsh operating conditions they face as the "heart" of a TBM, including ultra-heavy loads, large eccentric loads, and frequently varying loads. Besides, they need to meet critical standards such as high reliability and long service life. The material selection, design, manufacturing, and testing of them also presented immense difficulties. That's why they are considered the pinnacle of the industrial chain of large-scale, high-end, precision bearings.

An ultra-large diameter tunnel boring machine (TBM) is assembled at a production base of China Railway Engineering Equipment Group Co., Ltd. (CREG) in Hangzhou, east China's Zhejiang province. (People's Daily Online/Long Wei)

To finalize the design for main bearings, the Chinese research and development team experimented with hundreds of materials and processes, conducted thousands of theoretical verifications and design optimizations, and analyzed tens of thousands of inspection and test data sets.

In collaboration with leading specialty steel companies in China, CRCHI conducted in-depth research on material elemental matching and methods for controlling impurities and carbides, ultimately overcoming the bottleneck in the materials used for main bearings.

On October 12, 2023, a TBM main bearing with a diameter of 8.61 meters rolled off the production line at a CRCHI facility in Changsha, central China's Hunan province. It was the world's largest-diameter main bearing for TBM, boasting the heaviest weight and highest bearing capacity.

"It marked that China has become a global leader in the development and manufacturing of ultra-large diameter main bearings. Chinese-produced TBM main bearings now cover the full range from small to ultra-large diameters," said Liu Feixiang, chief scientist of CRCHI.

Additionally, Chinese enterprises are consistently moving towards intelligent and automated TBM operations, exploring autonomous excavation and remote control capabilities.

For instance, China's independently developed TBM "Linghang" is equipped with a system to monitor the status of key components in real-time, including the wear and temperature of cutting tools and slurry circulation pipes. It also provides damage predictions, effectively improving the construction efficiency.

The "Linghang" TBM also provides functions of intelligent excavation, intelligent assembly, advanced geological forecasting, and tail-end seal safety warnings. Therefore, it can automatically adjust parameters and excavate in ordinary geological conditions and can be controlled remotely from the ground surface under special circumstances.

Chinese TBM manufacturers are continuously expanding into overseas markets.

In 2012, China exported its first domestically produced TBM after China Railway won the bid for a metro construction project in Kuala Lumpur, Malaysia. During the construction, the "China Railway No. 50" TBM erected an average of eight rings per day, achieving over ten rings per day for seven consecutive days, setting a new record for metro TBM tunneling in Malaysia.

In 2015, China's "Zhang Heng" and "Zhan Tianyou" TBMs won contracts for metro projects in Singapore. In 2016, a rectangular pipe jack TBM was awarded another contract, pioneering the entry of China's specialized TBMs into overseas markets.

In 2019, the "China Railway No. 699" TBM won a bid for a railway project in northern Italy, marking the first application of China's advanced tunneling equipment in a country of European Union. In the same year, two domestically produced TBMs were contracted for a Paris metro construction project in France.

"All these demonstrate the recognition for the comprehensive strength of China's TBM brands by the international high-end market," said Zhang.