Dredged material management in immersed tube tunnel construction

摘要

Four case histories are described approximately 10 years apart, where unique solutions were implemented in the disposal of dredged materials for immersed tube tunnel construction. The earliest project in the 1970s used the dredged materials to construct a manmade island for the Second Hampton Roads Crossing in Virginia. The second project, the Fort McHenry Tunnel in Baltimore, built in the 1980s, separated clean and contaminated sediments and used the materials to reclaim the nearshore confined disposal facility (CDF) as a modern container terminal. The third, the Ted Williams Tunnel built in the 1990s in Boston Harbor, used large scale solidification/stabilization for contaminated sediments in an upland CDF. The most recent project, the Marmaray Rail Tunnel Crossing under the Bosphorus, will utilize a CDF for contaminated sediments - the first facility of its type in Turkey. The four projects illustrate a dramatic increase in dredging and disposal costs in the past three decades due primarily to continually tightening environmental restrictions. Furthermore, the escalating disposal costs threaten the economic feasibility of an otherwise attractive method of subaqueous tunnel construction.