"Start!" Recently, with a clear sound coming out of the walkie talkie, and with the rumbling noise, the blades of "Yongping" tunnel boring machine (TBM) slowly rotated, and the machine moved forward slowly, indicating the commencement of the TBM construction of the Shantou Bay submarine tunnel of Shantou-Shanwei High-speed Railway, the world's first single hole double track high-speed submarine railway tunnel with a design speed of 350 km/h. It is learned that Shantou-Shanwei High-speed Railway is under the general contracting of China Railway Design Corporation, an enterprise in Tianjin Port Free Trade Zone. The Shantou Bay submarine tunnel is the TBM constructed submarine high speed rail tunnel with the largest diameter in the world, and the excavation diameter of the TBM cutter head reaches 14.57 meters.

　　"The maximum buried depth of the tunnel is 67 meters, and the maximum water depth is 10 meters. The TBM will go through complex stratums, including long-distance crossing of 809 meters of full-section granite segments, with the maximum rock layer strength up to 166 MPa, and the maximum stone diameter of 5 meters." According to Li Jingzeng, manager of Shantou-Shanwei High-speed Railway general contracting project department of China Railway Design Corporation, the construction of the Shantou Bay submarine tunnel has encountered many world-class problems, which pose severe challenges to the constructors.