Recently, the control project of the second phase of the Yongzhou Expressway double track project, the Jintang Subsea Tunnel, has officially started construction. This major project, designed by China Railway Fourth Survey and Design Institute and constructed with the participation of China Railway 14th Bureau, will become the world's longest underwater highway shield tunnel with a total length of about 11.59 kilometers.

The tunnel is a key part of the second phase of the Yongzhou Expressway double track project, with a total length of approximately 18.05 kilometers. It is constructed according to the standard of a two-way six lane expressway and designed for a speed of 80 kilometers per hour. Tunnel engineering has significant characteristics of "super large, super long, and super deep". During construction, a 16 meter ultra large diameter shield machine will be used to cross complex and variable strata such as hard rock, soft soil, and soft hard interaction over long distances. The construction team needs to complete multiple difficult tool changing operations in a high-pressure environment, and ultimately achieve millimeter level high-precision docking under deep-sea conditions, which poses a world-class technical challenge.

The project faces multiple challenges: there are dense buildings along the route, and there are intersecting parallel sections with the under construction Yongzhou Railway Tunnel, making construction coordination difficult; The geological conditions are extremely complex, with extremely high strength bedrock known as the "diamond layer", while soft soil layers with high content of sticky particles are like "rice cakes". The uneven hardness of the composite strata greatly increases the risk of shield tunneling and tool replacement.

As a key component of the Shanghai Zhoushan Ningbo Cross Sea Passage and the Zhejiang Yiyongzhou Grand Passage, the completion of the second phase of the Yongzhou Expressway double track project will effectively improve the national highway network, strengthen the development of Ningbo Zhoushan integration, and have important strategic significance for promoting the integration of the Yangtze River Delta, enhancing the transportation carrying capacity of the Hangzhou Bay area, improving the transportation efficiency and emergency support capacity of the Yongzhou Passage. Editor/Xu Shengpeng