Flotation stability analysis of the immersed tubes in Kaohsiung Cross Harbor Tunnel

Kaohsiung Cross Harbor Tunnel is the first harbor cross tunnel in Taiwan, Republic of China. Its main structure is composed of six reinforcement concrete immersed tubes and two insitu ones. In analyzing the flotation stability of these precast immersed tubes, according to BSI specification, the stability in fabrication yard, after outfitting, during towing and sinking and after placing on seabed have all been taken into considerations. In the analysis, we suggest to use the reliability theorem to decide the reasonable range of concrete density and seawater density. Four kinds of figures are used to predict the stability results and some methods are suggested to solve the problems. In general the level of the tunnel along its longitudinal direction has some differences, and the height of the immersed tubes shall be changed in accordance with. By this irregular shape and small freeboard, the stability can not be decided by metacentric height. We have therefore developed programs to analyze the small freeboard and irregular immersed tubes.