CURRENT DEVELOPMENTS AND TECHNICAL ISSUES OF UNDERWATER TRAFFIC TUNNEL—DISCUSSION ON CONSTRUCTION
SCHEME OF TAIWAN STRAIT UNDERSEA RAILWAY TUNNEL
Abstract: Compared with other means of transportations， underwater tunnel has its own advantages, so it has been developed quickly at home and abroad in recent years. However, unlike mountain tunnel, underwater tunnel has its own characteristics and technical challenges. After in-depth analysis of the huge advantage of underwater tunnel compared with bridge， the current development stage of underwater tunnel at home and broad is introduced. The construction types of underwater tunnels including drill and blast method, shield method, immerged tube method and submerged floating tunnel are particularly illuminated. The scopes include their characteristics, technical difficulties, application conditions and some related problems; and their advantages and disadvantages are also discussed. The difficulties and key technologies in design and construction of underwater tunnel are summarized. Based on above-mentioned construction outlines, the construction scheme of Taiwan Strait subsea railway tunnel is thoroughly discussed, including the rationality of underwater railway tunnel, cross -section design and construction key points. Finally, some new concepts of underground projects construction such as underwater tunnel are put forward; and their key major technologies are summarized. These above-mentioned key technical points and suggestions will provide valuable references to the construction of underwater tunnel, especially for the construction of large subsea tunnel in China.
Key words: subsea tunnel; underwater tunnel; Taiwan Strait Subsea Tunnel; drill and blast method; shield method; immersed tube method; submerged floating tunnel
Ⅰ.INTRODUCTION
Ferries, bridges and underwater tunnels are the main method to cross the rivers, lakes and seas. Although having advantage in less investment, ferry is becoming incompatible to the fast-paced modern city transportation. Limited by its small traffic, long waiting time, the impact of climate and other unfavorable factors the way of ferry would rarely be in consideration. Increasingly, when we need to across rivers, lakes and seas, choices usually are given between underwater tunnels and bridges. Choosing a bridge or an underwater tunnel should be based on a comprehensive comparison and demonstration of specific construction conditions such as shipping, hydrology, geology, ecological environment and construction cost, and so on[1～5]. After demonstration, underwater tunnels have the following advantages over bridges:
ⅰ. Strong resistance to war damage, natural disasters (such as earthquakes) and unexpected incidents.
ⅱ. Not encroaching on the navigation clearance, not destroying shipping, not interfering with on-shore service facilities, not affecting the ecological environment in the sea area, having advantage of avoiding the impact of noise and dust on the surrounding environment, which is in favor of environmental protection.
ⅲ. Stable and unobstructed traffic capacity has little effect by the weather and climate change, .
