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Engineers in New York City designing a replacement for the Whitehall Ferry Terminal in lower Manhattan must deal with subsurface challenges in the form of three subway tunnels and one highway tunnel. Because of the sensitivity of the old tunnels, the three-year, $95-million project will require that 42 in. (1,050 mm) diameter steel isolation sleeves be placed around 36 in. (900 mm) diameter steel casings for 42 of 130 new caissons. Rotary drilling will place the casings 6 ft (2 m) into bedrock below the tunnel bottom. The existing terminal, which was damaged by fire in 1992, is at the Manhattan end of the Staten Island Ferry and is used by more than 60,000 people each day.
The sleeves around the caisson casings isolate loads from...
