On the morning of the 26th, China's largest diameter bay shield tunnel—the Shantou Bay Tunnel—began tunneling, marking a breakthrough in tunnel construction. The tunneling task is undertaken by this shield machine, currently the largest diameter shield machine in China. It has a diameter of 15.01 meters, equivalent to a five-story building, a total length of 130 meters, a total weight of 4,600 tons, and consists of tens of thousands of components. It is equipped with functions such as advanced geological forecasting, advanced drilling, and cutterhead telescopic swinging, and is specially developed and customized for the Shantou Bay Tunnel in China. Tunnel construction can be divided into different forms such as shield tunneling, immersed tube placement, and manual excavation. After comparing multiple schemes, the Shantou Bay Tunnel adopts shield construction. The Shantou Bay Tunnel is located between the existing Bay Bridge and Queshi Bridge, and consists of an undersea tunnel, the Nanbin South Road interchange, and north bank connecting works. The Bay Tunnel has a total length of 6,680 meters, with dual six-lane carriageways, and the tunnel has three layers: a smoke exhaust passage, a traffic passage, and a personnel evacuation passage. Once completed, it will have all-weather traffic capacity, greatly alleviating the traffic bottleneck caused by typhoons and other impacts on the bridge, and is of great significance for promoting the development of the "one bay, two banks urban pattern" and highlighting the status of the central city in eastern Guangdong.
Complex geological conditions and extremely high construction difficulty
The Shantou Bay Tunnel is China's first shield tunnel located in an area with seismic intensity of 8. The geological conditions are extremely complex, and the construction difficulty and risks are extremely high.
China divides seismic intensity into 12 degrees. An earthquake of intensity 8 can cause: damage to buildings, subgrade collapse, and rupture of underground pipelines. Building a bay tunnel in an area with seismic intensity of 8 is a world-class challenge and engineering problem. The builders formed a scientific research team, conducted simulation experiments on relevant seismic structures in the early stage, specially designed the segments at the interface of soft and hard rock and under the main navigation channel, and adopted a series of shock absorption measures to prevent earthquake damage to the tunnel structure. In addition, the bay geology is complex and uneven, with soft silt and hard bedrock appearing irregularly.
Yang Shujiang, project manager of the Shantou Bay Tunnel of China Railway Tunnel Group Co., Ltd.: Relative to the weak bearing capacity of the foundation, the tunnel using an undersea shield tunnel may cause the shield machine to pitch or sink, equivalent to performing a ritual in a tofu, and the equipment itself weighs 4,600 tons. The construction difficulty is currently second to none in China.
The tunnel is buried only about 12 meters deep under the main navigation channel, while the diameter of the shield machine exceeds 15 meters, which may cause the equipment to float and the undersea section to collapse. The builders have adopted new methods such as shifting the center of gravity of the shield machine and the cutterhead backward and reinforcing the foundation to ensure safe advancement.