The inspiration for the "underground dragon" shield machine actually comes from a mollusk

Produced by: Science Popularization China

Author: Liu Xin (University of Science and Technology of China)

Producer: China Science Expo

In 1997, when China started to build the Qinling Tunnel, the technical limitations forced us to seek help from Germany and purchase two shield machines worth 350 million yuan. These two machines were not even new. Their frequent failures were like an insurmountable gap. Every time, we had to wait for foreign engineers from afar to come and repair them. This not only delayed the progress of the project, but also deeply hurt the hearts of every Chinese engineer.

When we were building the Hong Kong-Zhuhai-Macao Bridge, we once again faced the severe test of technological blockade. The German company Wilt asked for a sky-high price - 700 million yuan for a tunnel boring machine! Not only that, the German experts also arrogantly asserted: "Even if Chinese engineers are given another 100 years, they will not be able to build a tunnel boring machine!" This is not only a heavy economic pressure, but also a great insult to our national dignity.

We were determined to conduct independent research and development! In 2008, my country's first composite shield machine with independent intellectual property rights, China Railway No. 1, was born!

On April 25, 2008, the "China Railway No. 1" shield machine rolled off the production line in Xinxiang, Henan.

(Photo source: Beijing Daily)

The shield machine, also known as the shield tunnel boring machine, is a high-tech special engineering machinery for tunnel excavation. As the name suggests, the shield machine uses the "shield method" to work. "Shield" means "protection", which refers to its shield shell, and "construction" means "construction", which refers to the assembly of pipe segments. It can be simply understood as: a cylindrical steel component that moves forward along the axis of the tunnel while excavating the soil. Its shell can play a temporary support role for the excavated tunnel section that has not yet been lined, bearing the pressure of the surrounding soil layer, and sometimes also bearing the groundwater pressure and keeping the groundwater out.

Working principle of shield machine

(Image source: Baidu Encyclopedia)

The inspiration for the shield method can be found in a small natural architect, the shipworm. The shipworm is a mollusk that lives in the ocean. It feeds on wood and can drill holes in wooden boards and live there.

Shipworm

(Photo source: poi-australia website)

The sharp and serrated shell at the front of the shipworm is its weapon for penetrating wooden boards and opening up space. This structure is very similar to the huge cutter head at the front of a shield machine, which uses a huge cutter head to go underground like a long steel dragon, "eating" rocks and soil while rotating its head.

The design inspiration of the shield machine was first obtained by French engineer Bruno in the late 18th century from the phenomenon of shipworms drilling holes. Bruno observed that when the shipworms drilled through the wooden board, they would secrete liquid on the hole wall, forming a tough protective shell to resist the expansion of the wooden board after it got wet and prevent it from being flattened. This natural phenomenon inspired him to propose the principle of tunneling with a shield machine, and the "open hand-drilled shield machine" designed based on this was awarded a British patent.

When we turn our attention to the middle and rear parts of the shield machine, we will find the complexity and delicacy of its structure. The middle and rear parts of the shield machine integrate the solid protection of the front and rear shields, as well as a vital hydraulic drive system, in which the hydraulic jack is the source of its power, just like the muscle fibers in the strong body section of the shipworm. At the same time, in order to make the tunnel more stable, the shield machine will automatically assemble a ring of concrete segments on the inner wall of the tunnel every time it moves forward a certain distance, and the gap between the lining segments and the tunnel wall must also be filled with mortar to maintain the stability of the overall lining layer and prevent water from leaking into the tunnel.

Shipworm (Image credit: Blue Zoology)

When it comes to waste disposal, there is an amazing resonance between the shield machine and the shipworm. The shield machine's built-in efficient conveyor belt system can quickly clean up a large amount of waste generated during excavation, ensuring the cleanliness and efficiency of the work site. The shipworm, a mollusk living in the ocean, also has an efficient waste disposal mechanism. They quickly excrete metabolic waste through special pipes at the back of their bodies to keep their bodies clean. This ingenious design of nature not only helps shipworms survive in harsh environments, but also provides valuable biological inspiration for humans.

China Railway Tunnel Bureau's large shield machine family portrait

(Image source: The Paper)

Today, China's shield machines can not only cross mountains and ridges, but also cross rivers and seas. They are widely used in various tunnel construction projects, and even successfully completed the Yangtze River shield project in the China-Russia natural gas transmission project. This series of achievements not only demonstrates the excellent performance of China's shield machine technology, but also reflects China's strong strength in the field of infrastructure construction.

"Qiyue" shield machine

(Photo source: Wen Wei Po)

In 2012, the first TBM of China Railway Equipment was exported, opening a new chapter in the internationalization of China's TBM. In the following years, China Railway Equipment gradually became a world-renowned leader in the TBM industry, with its products exported to many countries and regions, winning wide recognition and praise in the international market.

my country's shield machine will go to the birthplace of shield machines and manufacturing powerhouse in the world to build subways

(Image source: Science and Technology Daily)

From nothing to something, from weak to strong, the development of China's shield machine is a struggle full of challenges and glory. This process not only demonstrates China's independent research and development strength and innovative spirit, but also shows the great power of Chinese wisdom and national spirit. Just as the shield machine keeps moving steadily underground, China is also moving forward firmly on the road of scientific and technological innovation, building a solid backbone for the country.