29.2 km Hangzhou Bay rail bridge passes major structural milestone

Construction of the 29.2 km Hangzhou Bay Cross-Sea Railway Bridge has passed another major milestone following closure of its northern and southern navigation channel structures, bringing the world's longest cross-sea high-speed railway bridge closer to completion.

The bridge will carry two high-speed railway tracks between Jiaxing and Ningbo in Zhejiang Province as part of the 301 km Nantong-Ningbo high-speed railway. Designed for operating speeds of up to 350 km/h, it forms a major component of China's coastal high-speed rail corridor across the Yangtze River Delta.

Overall construction progress has exceeded 90%, with the project now moving from major structural works towards completion of the bridge deck systems and ballastless railway track.

The bridge comprises northern, central and southern navigation channel bridges together with extensive approach structures across shallow and deeper sections of Hangzhou Bay. The north channel bridge recently achieved closure approximately 570 m offshore from Haiyan county, following completion of the final welded section.

This structure is particularly significant because of its 450 m main span, described as the longest currently under construction for a high-speed railway bridge carrying ballastless track. The 932.7 m long cable-stayed bridge uses a hybrid steel box-truss girder, combining a steel box girder below with truss elements above.

Controlling deformation has been one of the key engineering challenges. A 450 m flexible span must still satisfy the millimetre-level alignment tolerances required by high-speed railway systems, where excessive deformation can affect both track geometry and dynamic train performance.

The southern navigation channel bridge, closed several days earlier, has a total length of 814.5 m and a 364 m main span capable of accommodating vessels of up to 3,000 deadweight tonnes. Its closure used a double-sided incremental launching technique adapted to the difficult marine conditions within Hangzhou Bay.

Those conditions are among the project's defining challenges. The bay experiences a tidal range approaching 9 m, strong currents, frequent winds and an aggressive saline environment. Continuing seabed scour and deposition further complicate offshore foundation and superstructure construction, while suitable marine working windows can be limited.

To maintain alignment during critical closure operations, project teams have used BeiDou satellite positioning, digital monitoring and extensive instrumentation across bridge towers, girders and temporary supports. Stress, cable force and displacement have been monitored continuously, while wind-resistant devices and transverse restraints have been used to control the closure geometry. Some operations were also scheduled during periods of more stable nighttime temperatures to limit thermal deformation.

All offshore pile foundations and pier shafts have now been completed. With the north and south navigation bridges connected, attention is shifting towards the remaining central navigation channel bridge, installation of permanent bearings, stay-cable adjustments, bridge deck works and eventual track installation.

Once operational, the crossing will provide a direct high-speed rail connection across Hangzhou Bay, avoiding the much longer land route around the coastline and strengthening rail connectivity between cities across the Yangtze River Delta.