Breakthrough under Zhanjiang Bay Undersea Tunnel of the Guangzhou-Zhanjiang High-Speed Railway

The undersea tunnel of the Guangzhou-Zhanjiang High-Speed Railway, spanning from Guangzhou to Zhanjiang in Guangdong Province, successfully broke through under Zhanjiang Bay on March 15th. This marks an important stage in the construction of the key control project along the entire line. Upon completion and opening to traffic, the Guangzhou-Zhanjiang High-Speed Railway will enable travel between Guangzhou and Zhanjiang city centers within 90 minutes.

Li Jing, the chief planner of the Department of Transport of Guangzhou Province , explained that with the highway network in the Guangdong-Hong Kong-Macao Greater Bay Area being improved, the concept of a "Greater Bay Area on the track" is being rapidly advanced. The world-class airport clusters and port clusters within the area is rapidly taking shape. The integrated development of the Guangdong-Hong Kong-Macao Greater Bay Area is accelerating, achieving high-level connectivity within and outside the Greater Bay Area, promoting the efficient circulation of people, logistics, capital, and information.

The Zhanjiang Bay undersea tunnel is a key control project along the entire Guangzhou-Zhanjiang High-Speed Railway line. The tunnel spans a total length of 9,640 meters, and the shield tunneling section measures 7,551 meters in length with a diameter of 14.33 meters. The tunnel is constructed with a single shield machine driving in one direction, and is designed as a single tunnel with double tracks, making it the longest single-head shield tunneling distance for a high speed railway under the sea in China. It is characterized with the large excavated section, challenging geological conditions, abundant discarded mud, a tendency for clogging, and crossing urban areas under the sea. The construction of the tunnel effectively retains the existing urban skyline of Zhanjiang Bay, minimizes the impact on air traffic, and effectively avoids the impact of typhoons on the safety of high-speed railway operations.

The Guangzhou-Zhanjiang high-speed railway is an important coastal corridor of national "Eight Vertical and Eight Horizontal" high-speed railway network. The main line of the Guangzhou-Zhanjiang high-speed railway starts from Guangzhou Station, heads west through cities like Foshan and Zhaoqing, and terminate at Zhanjiang North Station. The investment of the project is estimated to be 99.8 billion yuan. The new double-track line extends 401 kilometers, with a designed speed of 350 kilometers per hour, will have 9 new stations, including Foshan Station, Pearl River Delta Hub Airport Station, and Zhanjiang North Station. It is expected to be operational by the end of 2025. Upon completion, the rail travel time between the central urban area of Guangzhou and Zhanjiang will be reduced to about 90 minutes, connecting the western regions of Guangdong to the 350 km per hour high-speed rail network.

The Yongxing shield tunneling machine, with a diameter of 14.33 meters, is about as tall as a 5-story building. Behind the slowly rotating cutter head, which is over a hundred meters long, is its "body" composed of tens of thousands of parts.

"The design of Zhanjiang Bay undersea tunnel is a single tunnel with double tracks, which can accommodate the future high-speed trains traveling in both directions. This is why it has such a large excavation section and uses such a large diameter  shield tunneling machine." said Yin Yihao, an engineer from China Railway 14th Bureau Group, which was responsible for the tunnel's construction

The Zhanjiang Bay undersea tunnel of the Guangzhou-Zhanjiang high-speed railway crosses the seabed of the Zhanjiang Bay and the urban area of Zhanjiang, with the shield tunneling machine progressing like an iron earthworm, "eating soil" as it moves forward. The huge rotating cutter head at the front acts like the head of an earthworm, with densely packed cutter heads being its teeth. The cutter head continuously rotates and cuts through rock and soil, "chewing up" the rock and mud into the pipeline pump's "stomach," then are transported to the surface. While "eating soil,", it automatically assembles one ring of tunnel lining every 2 meters. In this way, as the shield tunneling machine excavates and assembles simultaneously, the tunnel takes shape as the machine passes through.

The "Yongxing" shield tunneling machine will not only encounter silty clay that can clog the cutter head in the Zhanjiang Bay undersea tunnel, but also encounter iron-rich cemented quartz sandstone, which wears down the cutting tools. The dense underground pipeline networks and towering skyscrapers above also pose great challenges to the operation and performance of the shield tunneling machine.

"By improving the construction of the shield tunneling machine's slag disposal system and optimizing the material of the cutters, we have effectively improved the construction efficiency in such complex geological strata." said Cai Mingcong, Chief Mechanic of the Guangzhou-Zhanjiang Railway Project of the China Railway 14th Bureau Group Co., Ltd.

At present, the construction of bridges, tunnels and other projects along the entire line is progressing simultaneously. "Currently, the overall progress of the Guangzhou-Zhanjiang High-Speed Railway construction stands at 93% for the track foundation, 91% for bridge construction, and 86% for tunnel construction. Track laying, building construction, and 'four-electricity' projects have all started comprehensively. The project is striving to meet the conditions for operation by the end of 2025." said Hu Jijun, Deputy Director of the Engineering Department of Guangdong Guang-Zhan Railway Co., Ltd. 

Reprinted from: China Traffic News