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 Back to Projects
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Project:
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Excavation Support for Transit Tunnel
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Location:
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Boston, Massachusetts
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Client:
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Modern Continental Construction Company
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Description:
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Two parallel tunnels segments, part of the Massachusetts Bay Transit Authority's Silver Line
Project were constructed under two existing buildings in a downtown section in Boston. Due to
the historical significance of the buildings, it was necessary to preserve the structural
integrity during the tunnel construction. Ground freezing was selected as the only method that
could perform the required groundwater control and excavation support.
The ground freezing was completed in two stages. During the first stage, a groundwater cut-off
wall was drilled and installed around the perimeter of the construction zone. After formation of
the frozen cut-off wall, drilling and installation of the tunnel crown freeze was initiated from
within the subsurface parking area. A system of underpinning beams was installed to transfer the
load of the building to a series of drilled piles.
The entire zone above both tunnels was frozen, and tunneling operations commenced using the New
Austrian Tunnel Method. Following the installation of the final tunnel lining, a heat exchanger
circulated water from the adjacent channel, was used to accelerate the thawing process.
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