Main structure of ultra-deep underground high-speed rail station completed in Jiangsu

The main underground structure of China's longest ultra-deep, ultra-large foundation pit high-speed railway station was completed on Wednesday in Jiangsu province, marking a pivotal advance.

The milestone was reached at the Haimen North Station construction site in Nantong city, a key node on the under-construction Shanghai-Nanjing-Hefei High-Speed Railway.

Designed around two platforms and six tracks, the station spans three underground levels: transfer corridors on the first, high-speed rail platforms on the second, and a floor reserved for future intercity rail lines on the third.

Stretching 1.8 kilometers in continuous length and plunging to a maximum depth of 29.4 meters, the dig displaced about 1.48 million cubic meters of earth. The retaining structure employs 1.2-meter-thick diaphragm walls reinforced by five layers of concrete struts.

The station's northern end is designed to connect to the planned Nantong new airport, with plans to transform Haimen north station into a comprehensive transportation hub integrating high-speed rail, aviation, urban transit, buses, and taxis under one roof.

The station sits atop a geological profile characterized by water-saturated silty soil, fine sand, and muddy clay. Construction teams have likened the work to "building a high-speed railway inside a block of tofu".

Carrying a top-level structural safety grade, the project demands that both the maximum horizontal displacement of retaining structures and surface settlement be kept within three centimeters.

To meet these conditions, the construction team developed and deployed three integrated digital management systems. Across the entire site, 1,105 drainage wells were installed, with automated water level and flow sensors enabling precision zonal control and demand-responsive dewatering.

A network of 2,185 axial force and structural monitoring points feeds a real-time system that collects, transmits, analyzes, and issues alerts, keeping deformation in check and allowing risks to be identified and neutralized before they can escalate.

With the main underground structure now complete, Haimen North Station moves into its next phase of dismantling temporary supports, installing mechanical and electrical systems, and constructing the aboveground station building.

Once operational, the line will open a new corridor connecting the Shanghai, Nanjing, and Hefei metropolitan clusters, further strengthening the Yangtze River Delta's railway network.