Abstract：
Restricted by terrain conditions under water and on shore, the longitudinal profiles of underwater highway tunnels generally present the trend of being steep at the ends and flat in the middle section. Since the maximum longitudinal gradients at the tunnel entrance and exit directly determine the size of a tunnel, a gradient of no more than three or four percent is generally adopted in the design according to the current effective standards. While the vehicle type, longitudinal gradient combinations, and standards for air quality are different for each tunnel project, in practice the longitudinal gradient should be evaluated by scientific calculation and analysis based on a large number of survey data. Using the immersed tunnel of the HongKong-Zhuhai-Macao sea-crossing project as an example, this paper elaborates upon the argument for the maximum longitudinal gradient of the immersed tunnel and proves the rationality and science of the designed maximum longitudinal gradient at the tunnel entrance and exit. It also shows that the maximum longitudinal gradient is an important indicator that must be determined at the pre-design period for underwater highway tunnels. For underwater tunnel projects, systematic research and demonstration should be carried out according to various influential factors for longitudinal gradients in order to determine a reasonable value.
2013, Vol. 50 