Key progress in the construction of an underwater section of a 2,000-kilometer high-speed railway linking Shanghai in East China and Chengdu in Southwest China's Sichuan province drew widespread attention on Chinese social media over the weekend.

The topic "China to launch high-speed railway under the Yangtze River" trended on Weibo at the end of March.

The project, with a total investment of 500 billion yuan ($72.8 billion), is among the country's major projects included in the outline of the 15th Five-Year Plan (2026-30), according to public information.

On March 29, the "Linghang" shield tunneling machine completed a record 11.18-km underwater excavation after 23 months of safe tunneling, passing beneath the southern embankment of the Yangtze River.

The Shanghai-Chongqing-Chengdu high-speed railway, including the underwater section from Chongming in Shanghai to Taicang in Jiangsu province, is a backbone route in the national "eight vertical and eight horizontal" high-speed rail network. The project is expected to generate up to 1.5 trillion yuan in added value along the industrial chain, benefiting more than 20 smaller cities along the route, according to a China Central Television report.

Known as China's longest and largest cross-river tunnel for high-speed rail, the Chongming-Taicang Yangtze River tunnel has a total length of 14.25 km and has set multiple global records, according to an article published on the official WeChat account of China Railway Group.

Using the Linghang shield tunneling machine, the project requires a single-drive excavation distance of 11.325 km, with a maximum cutter-head diameter of 15.4 meters and a maximum depth of 89 meters beneath the Yangtze River. The tunnel is designed to accommodate trains operating at speeds of up to 350 km/h.

These achievements will enable high-speed trains to cross the Yangtze River without slowing down, China Railway Group said.

"At a speed of 350 km/h, the required precision is within the millimeter range," Wang Yi, deputy equipment manager of the project, was quoted in a ThePaper.cn report.

Wang said underwater tunnels are affected by factors such as water pressure and geological settlement, and even slight deviations in alignment can affect safety and passenger comfort. This places stringent requirements on structural precision, track smoothness and resistance to external interference.

"This is not only a breakthrough in technical indicators, but also underscores China's leading position in high-speed rail underwater tunnel construction. More importantly, it demonstrates China's capability in mastering core technologies for ultra-high-speed underwater tunnels, providing replicable and scalable experience for similar projects in the future," Wang said.

A single shield tunneling machine, composed of more than 20,000 parts and components, is widely regarded as an important indicator of a country's manufacturing capability due to its complex systems and high precision requirements.

As a key contributor to the project, the Linghang machine reflects China's progress in the sector over the past three decades, from a pure importer to an industrial leader, according to the CCTV report.

In 2002, the development of shield tunneling machines was included in a national-level program, marking the start of China's localization drive. In 2004, the country's first metro shield machine was unveiled in Shanghai and used in soft soil.

Over the past two decades, domestically developed shield tunneling machines have made continuous breakthroughs, with increasing levels of innovation and intelligence. Chinese-made machines are now exported to more than 40 countries and regions, accounting for about 70 percent of the global market.