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 Back to Projects
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Project:
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Ground Freezing - Access, Vent, and Drop Shafts
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Location:
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Milwaukee, Wisconsin
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Client:
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J.F. Shea Company, Inc.
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Description:
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Three 210-foot deep shafts were required for the Lake Michigan South portion of the Milwaukee
Deep Tunnel projects. These shafts were located approximately 150-feet from Lake Michigan in
soils that varied from highly permeable sands and gravels to over consolidated glacial clays.
Groundwater conditions were artesian, with piezometric heads measuring 8 feet above the ground
surface. This condition could be detrimental to the freezing process as the boreholes used for
freeze pipe installation could actually be conduits for the pressurized groundwater, creating a
constant dynamic condition. Special drilling and borehole grouting techniques were implemented
to minimize the annular area between the boreholes and freeze pipes, thus choking off these
conduits.
Two of the shafts were of relatively small diameter and would be excavated using the raise bore
techniques. This method required that the shafts be frozen solid throughout the entire depth.
The heterogeneous soil conditions and corresponding thermal properties required the use of a
time-dependent heat transfer computer program to model the thermal regime in order to coordinate
the contractor's excavation schedule with the freezing process.
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