Core Insights - The "Yongzhou" shield machine has achieved over half of its tunneling progress for the world's longest underwater high-speed rail tunnel, marking a significant milestone in the construction of the Ningbo-Zhoushan railway [1][3]. Group 1: Project Overview - The Jintang underwater tunnel is a key project of the Yongzhou railway, stretching 16.18 kilometers, with the shield section measuring 11.21 kilometers [3]. - The tunnel employs two shield machines, "Yongzhou" and "Dinghai," which are advancing simultaneously from both Ningbo and Zhoushan sides [3]. Group 2: Technical Challenges - The geological conditions along the Jintang underwater tunnel are extremely complex, requiring the crossing of various risk sources such as sea dikes, docks, and shipping lanes [4]. - The maximum depth of the underwater section reaches 78 meters, with a maximum water pressure of 8.4 bar, equivalent to nearly 1 ton of weight on an adult's palm [4]. - The Ningbo side has experienced frequent geological changes, necessitating high-pressure tool changes, with the "Yongzhou" machine completing 12 geological transitions and changing tools over 2400 times [4]. Group 3: Strategic Importance - The Yongzhou railway is a major project in China's Medium- and Long-term Railway Network Plan (2016-2030), with a total length of 76.4 kilometers and a design speed of 250 kilometers per hour [4]. - Once operational, the project will connect Zhoushan, the only city in the Yangtze River Delta without a railway, to the national railway network, significantly enhancing regional integration and development [4].

Core Viewpoint - The approval of the feasibility study report for the Ningbo Qijia Mountain to Zhoushan Jintang section of the Ningbo-Zhoushan Expressway double line marks a significant step forward for the construction of the world's longest underwater dual-direction six-lane highway tunnel, indicating that the second channel of the Ningbo-Zhoushan Expressway will commence full construction [1][3]. Group 1: Project Overview - The total investment for the Ningbo-Zhoushan Expressway double line is approximately 31.4 billion yuan, with a total length of about 46 kilometers, designed to a dual-direction six-lane highway standard and an overall design speed of 100 km/h [3]. - The project consists of three segments, with the Jintang to Dasha segment (rail and road combined bridge) costing about 10.9 billion yuan and expected to be completed by 2028, the Ningbo Qijia Mountain to Zhoushan Jintang segment (underwater tunnel) costing about 15.7 billion yuan and expected to be completed by 2030, and the Beilun Haosifang to Qijia Mountain segment costing about 4.8 billion yuan and expected to be completed by 2029 [3]. Group 2: Technical Details - The approved section of the Ningbo-Zhoushan Expressway double line is 18.1 kilometers long, featuring the world's longest underwater dual-direction six-lane highway tunnel, the Jintang Underwater Tunnel, which is 11.6 kilometers long and utilizes 16-meter shield tunneling technology [3]. - The construction of the tunnel presents significant technical challenges, including "super large, super long, super deep" characteristics, complex geological conditions, underwater precision alignment, and underwater tunnel dismantling [3]. Group 3: Strategic Importance - The construction of this project is crucial for improving the national highway network, promoting high-quality development in Zhejiang, accelerating the construction of the Yangtze River Delta urban agglomeration, and enhancing the transportation and emergency response capabilities of the Ningbo-Zhoushan cross-sea passage [4]. - Once the double line is fully completed, the total length of the Zhoushan connected island expressway will reach 120 kilometers, further solidifying its status as China's longest connected island expressway [4].