China News Service, Qingdao, October 2 (Reporter Hu Yaojie) On October 2, at a depth of 105 meters below the sea level in Jiaozhou Bay, Qingdao, Shandong, as the "Guo Signal" shield machine cutterhead reached the dividing mileage, the Qingdao Jiaozhou Bay Second Tunnel Service Tunnel, invested and constructed by Qingdao Guoxin Group and participated by the China Railway 14th Bureau, completed the shield excavation task, marking the completion of the shield excavation of the world's longest submarine highway tunnel.
According to reports, the Qingdao Jiaozhou Bay Second Tunnel Project has a total length of 17.48 kilometers, and the main body of the tunnel is 14.37 kilometers long. It is based on the layout of "dual main tunnels + intermediate service tunnels", with six lanes in two directions, and a design speed of 80 kilometers per hour. According to the different geological conditions of the Jiaozhou Bay sea area, the project adopts the "drilling and blasting + shield tunneling" combined construction method, excavating from the east and west sides of Jiaozhou Bay to Jiaozhou Bay, and docking in the sea. The shield section uses two super-large-diameter shield machines with a diameter of 15.63 meters and a shield machine with a diameter of 8.18 meters for excavation construction.
According to Wang Junping, the technical leader of the Qingdao Jiaozhou Bay Second Tunnel Project of the China Railway 14th Bureau, the project team has carried out targeted design optimization of the two shield machines. By reducing the distance between the cutters, the shield machine has enhanced its rock-breaking ability. It has also adopted the slag discharge system design of "screw machine + gravel box + gravel machine" for the first time in China to improve the slag discharge efficiency and reduce the risk of slag stagnation. It has innovated the shield stabilization and anti-seismic technology of the shield machine to improve the seismic resistance of the shield machine in hard rock formations and avoid abnormal damage to the cutters and main bearings.
In addition, facing the box culvert assembly operation under the narrow tunnel space, the project team used the world's first synchronous assembly of box culverts on a small shield to achieve trackless material transportation in the tunnel, and synchronized excavation and internal prefabricated box culvert assembly operations.
Focusing on the engineering problems of ultra-large-diameter shield tunneling through seabed hard rock and fractured zone formations over long distances, China Railway 14th Bureau collaborated with Shandong University, Beijing University of Technology, Beijing Jiaotong University, Central South University and other universities to jointly tackle key issues, undertaking three national key projects and unveiling projects, focusing on solving problems such as abnormal tool wear, low tunneling efficiency, risk of main drive failure, and risk of shield tail breakdown. At present, 17 utility model and invention patents have been formed, 20 papers and 2 construction methods have been completed.
It is reported that the Qingdao Jiaozhou Bay Second Tunnel was recognized by the World Tunnel Congress as one of the “50 landmark projects in the field of global tunnels and underground engineering.” Since the start of construction, it has ranked among the "Big Five" in the world. It is the world's largest undersea road tunnel. The amount of earth and stone excavated for the project exceeds that of Japan's Seikan Undersea Tunnel and the Channel Tunnel. It is the longest undersea road tunnel under construction in the world and will be completed after completion. Exceeding the Ryfylke Tunnel in Norway (14.3 kilometers); the world's largest cross-section submarine tunnel that crosses a large-scale fault; the world's highest water pressure super-large-diameter shield tunnel; the world's first super-large-diameter shield tunnel and a large-section drill-and-blast tunnel.
