China's deepest undersea high-speed rail tunnel, part of the Shenzhen-Jiangmen High-Speed Railway, has achieved a record excavation depth of 113 meters beneath the seabed in the Pearl River Estuary. The domestically developed tunnel boring machine (TBM), "Shenjiang-1," has worked continuously for over four years, advancing more than 4 kilometers. This critical phase of construction for the 13.69-kilometer Pearl River Estuary Tunnel involves navigating complex geological conditions, including 13 strata, five composite geology types, and six fault zones, with the TBM employing advanced excavation and lining assembly techniques. The 116-kilometer Shenzhen-Jiangmen line aims to reduce travel time between Shenzhen and Jiangmen to under an hour, bolstering connectivity within the Guangdong-Hong Kong-Macao Greater Bay Area.