China's first under-river high-speed railway tunnel began construction yesterday. The 10.1-kilometer tunnel is part of the Wuhan-Guangzhou passenger railway, running under the 210-meter wide Liuyang River. The project is to be completed in four months.
Located to the east of Changsha, the capital city of Hunan Province, the tunnel starts from the south side of Xiaoxiang West Road and goes under several expressways and the Liuyang River, a main waterway running through the central province.
The project is divided into two sections and contracted to two engineering groups of the China Railway Engineering Corporation respectively. The southern section includes the critical underwater track and about 80% of the construction will adopt the method of undercutting excavation.
The minimum distance from the top of the tunnel to the bottom of the river is merely 13 meters. Additionally, the instability of peripheral rocks will probably incur collapse and flooding during construction.
A total of 90 pipes filled with cement slurry will be hammered into the vault with a length of 18 meters, propping up the roof of the tunnel. Calculations show the underwater section will require 1,575 such pipes.
According to Pan Shengqiang, deputy director of the Changsha Reform and Development Commission, they abandoned a proposal to build a bridge across the Liuyang River for several reasons. The plan concerned so many government departments that it would have been difficult to coordinate the construction. Moreover, running through the center of Changsha City, the proposed bridge would have imposed a negative image on urban planning and economic development.
The construction of the southern section has started in five directions, and some 600 workers are working around the clock to excavate 2.4 meters per day in each direction.
The Liuyang River portion is to be completed in four months, and the 5.1-kilometer southern section will be finished by the end of August next year to link up with the new railway station of Changsha.
(China.org.cn by Huang Shan November 30, 2007)