Core Viewpoint - China Railway Construction Corporation (CRCC) is advancing multiple undersea tunnel projects to enhance regional connectivity along China's coastline using domestically developed technologies [1] Group 1: Project Details - The Yongzhou Railway's Jintang undersea tunnel is being excavated to a maximum depth of approximately 78 meters, utilizing China's first integrated shield tunneling system designed for high water pressure management [2] - The Qingdao Jiaozhou Bay Second Tunnel, spanning 17.48 kilometers, employs a combination of shield tunneling and conventional mining methods to navigate through hard rock and fractured zones [4] - The Shenzhen-Jiangmen Deep River undersea tunnel is advancing at depths reaching 116 meters, making it one of the world's deepest high-speed rail tunnels beneath the sea [4] Group 2: Completed Projects - The Jinpu Sea River Tunnel in the Bohai region, part of the Jinan-Qingdao high-speed line, has been completed, overcoming challenges such as corrosive saline soil through specialized anti-corrosion measures [5] Group 3: Technical Advancements - CRCC has established a comprehensive technical system that includes survey and design, construction management, core components, and digital operations, enhancing the efficiency of cross-sea tunnel projects [6]