China Completes Historic Caiyuanba Tunnel under Yangtze River, Setting Milestone for the First Under-Water High-Speed Railway Tunnel: New Travel Alert

Published on July 26, 2026

A monumental engineering milestone has been achieved with the structural completion of the Caiyuanba Yangtze River Railway Tunnel, marking China's first high-speed railway tunnel constructed beneath the Yangtze River. Extending 11.9 kilometers under Chongqing, this critical section connects western and southeastern China along the future Chongqing–Xiamen high-speed railway line. Once fully operational, the high-speed rail corridor will significantly improve transit speeds, regional integration, and passenger mobility between inland industrial centers and the coastal Fujian province.

Quick Summary

Record Under-River Crossing: The Caiyuanba Tunnel stretches 11.9 kilometers beneath the Yangtze River in the Chongqing municipality.
Chongqing–Xiamen Corridor: The tunnel serves as a vital crossing on a strategic high-speed line linking southwestern China with the southeastern coast.
Custom Engineering Technology: Construction teams utilized a custom-designed Tunnel Boring Machine (TBM) engineered for high water pressure and rocky riverbeds.
Strategic Rail Grid Milestone: The line forms part of the national "eight vertical and eight horizontal" network, which is 84% completed as of March this year.
Underwater Construction Surge: The project highlights a wave of advanced underwater rail tunnels, including the world’s deepest at Pearl River Estuary (116 meters).

Context and Background: Overcoming Challenges in High-Speed Railway Tunnel Engineering

The successful drilling of the Caiyuanba Yangtze River Railway Tunnel marks a major advance in underground transportation infrastructure, officially cataloged in construction reports from the National Railway Administration of China. Building a high-speed line under one of the world's busiest commercial waterways required navigating complex geological structures, rugged mountain terrain, and dense urban residential districts. Engineers had to design the path to protect municipal surface infrastructure and maintain riverbed stability.

This achievement aligns with transit data compiled by United Nations Tourism (UN Tourism) regarding transit capacity upgrades in major economic clusters. By establishing direct high-speed railway corridors, countries can disperse traveler flows, support regional logistics, and link distant urban zones. The tunnel serves as a vital component of China's long-term plan to build a faster, better-connected national transport grid.

Event and Incident Details: Core Parameters of the Caiyuanba High-Speed Railway Tunnel

The Chongqing–Xiamen high-speed railway is one of the 16 strategic rail corridors that make up the foundation of the country's national railway program. Once fully connected, the network will extend rail access from Gansu Province in the northwest down to Hong Kong, Shenzhen, and northeast to Harbin.

China Under-Water High-Speed Railway Tunnel Project Metrics:

Rail / Tunnel Project	Location & Waterway	Key Technical Parameters	Infrastructure Context
Caiyuanba Tunnel	Chongqing; under the Yangtze River	11.9 km long; built with custom high-pressure TBM	Connects Chongqing and Xiamen; strategic corridor link
Pearl River Estuary Tunnel	Guangdong; under Pearl River Estuary	Depth of ~116 meters (world's deepest)	Part of the Shenzhen–Jiangmen HSR corridor
Chongming–Taicang Crossing	Shanghai to Jiangsu	Under construction; upcoming completion	Connects Shanghai's Chongming Island to Taicang
China's HSR Network	Nationwide grid	Over 50,000 km operational; target 60,000 km in 5 years	84% of the "8 vertical and 8 horizontal" grid completed

To excavate through the river's alternating layers of hard and soft rock, crews deployed a custom-built Tunnel Boring Machine (TBM). This specialized equipment was designed to withstand extreme hydrostatic pressures deep below the riverbed, ensuring continuous structural accuracy, excavation efficiency, and on-site safety.

Risk and Impact: Water Pressure, Structural Stresses, and Urban Constraints

Building a long high-speed railway tunnel under a major river involves several technical risks and structural challenges:

Extreme Hydrostatic Pressure: Working deep below the Yangtze Riverbed subjects the excavation equipment to intense water pressure, requiring continuous monitoring of TBM seals.
Alternating Geological Strata: The transition between soft mud deposits and hard rock formations can cause TBM wear, requiring frequent maintenance.
Urban Surface Settling Risks: Drilling directly beneath densely populated residential districts in Chongqing requires careful controls to prevent ground settling.
Complex Ventilation Requirements: The 11.9 km length requires advanced ventilation systems to maintain air quality during both construction and future operations.
Coordination with River Traffic: Deep-underground works must avoid interfering with heavy commercial shipping traffic along the Yangtze River corridor.

What Engineers and Project Managers Are Saying

Project managers emphasize that the successful breakthrough of the Caiyuanba Tunnel proves that underground construction technologies are capable of handling high-pressure underwater environments. Planning representatives suggest that the lessons learned from this Yangtze crossing will benefit ongoing projects, including the Chongming–Taicang rail connection near Shanghai. Authorities state that after final track laying, signaling setup, and safety testing, the Chongqing–Xiamen corridor will be ready to transition to full passenger operations.

Practical Traveler Advice: Planning Your Travel on China's HSR Network

For international tourists and business travelers wishing to use China's high-speed rail lines, transit guides recommend the following actions:

Verify Route Openings Online: Confirm if specific segments of the Chongqing–Xiamen corridor are operational before planning your regional itinerary.
Utilize English Booking Portals: Book train tickets and reserve seats through verified ticketing apps, using your passport for identification.
Plan for Passport Verification at Stations: Arrive at major rail hubs early, as international travelers must pass manual passport checks at ticket gates.
Coordinate Transfers Between Urban Districts: In large cities like Chongqing, verify which train station your route departs from to avoid cross-city delays.
Pack for Multi-Hour Journeys: While high-speed trains are fast, cross-country routes can take several hours, so carry suitable travel essentials.

Broader Context: China's Expanding High-Speed Rail Network

By the end of last year, China’s operational high-speed rail network exceeded 50,000 kilometers, establishing it as the largest in the world. National infrastructure plans call for expanding this total to approximately 60,000 kilometers within the next five years, connecting additional regional cities. This rapid development has driven the construction of advanced underwater tunnels, helping transport networks overcome geographic barriers like wide rivers, bays, and estuaries.

Looking Ahead: Staged Openings and Upcoming Record Deep Crossings

Looking forward, construction teams are shifting focus toward completing track installation and signaling tests inside the Caiyuanba Tunnel. In Guangdong Province, work continues on the Shenzhen–Jiangmen HSR tunnel under the Pearl River Estuary, which will reach a record depth of 116 meters. These ongoing engineering projects will secure China's status as a leader in underwater rail tunnels, supporting faster and more efficient travel across the country.

Conclusion: A Faster, Better-Connected Rail System

Ultimately, the structural completion of the Caiyuanba Yangtze River Railway Tunnel brings the full Chongqing–Xiamen high-speed corridor closer to reality. By utilizing advanced TBM technologies, builders successfully navigated complex geological and urban challenges. Planning ahead and staying informed on new route openings will guarantee a comfortable travel experience across China's modern rail network.

FAQ: China's First High-Speed Rail Tunnel under the Yangtze River

What is the Caiyuanba Yangtze River Railway Tunnel?

The Caiyuanba Tunnel is an 11.9-kilometer railway tunnel located in Chongqing, China. It is the country's first high-speed rail tunnel constructed beneath the Yangtze River, forming a key link on the future Chongqing–Xiamen high-speed rail line.

How did engineers build the tunnel under the river?

Construction teams used a custom-designed Tunnel Boring Machine (TBM) engineered to withstand extreme water pressure and excavate through alternating layers of hard and soft rock deep below the riverbed.

How complete is China's national high-speed rail grid?

As of March this year, approximately 84% of the planned "eight vertical and eight horizontal" strategic high-speed rail corridors had been completed. The total operational network exceeds 50,000 kilometers.

What is the world's deepest underwater high-speed rail tunnel currently under construction?

The deepest tunnel is under construction at the Pearl River Estuary in Guangdong Province as part of the Shenzhen–Jiangmen high-speed railway, reaching depths of approximately 116 meters.

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