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SoilFreeze has extensive experience in providing shoring for deep shafts. Microtunneling
access, deep manhole construction, equipment recovery, and mining are all common
applications for frozen soil shafts. SoilFreeze maintains well-tested protocols
for keeping shoring walls watertight when penetrated, most commonly by tunnel boring
machines. Shaft construction may also be called for in densely populated urban developments
and limited overhead construction, such as below power lines or under elevated roadways.
SoilFreeze partners with highly skilled, local pipe installers to minimize social
disruption during installation and maintenance.
Design considerations: The deeper shafts go into soils
with high groundwater, the greater the anticipated hydrostatic pressure. A critical
design element, therefore, becomes how deep to install the freeze pipes (past the
excavation depth) to create
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an unfrozen “plug” below the base of the excavation.
Only the most specialized and experienced geotechnical engineer will be able to
analyze the natural soils to determine the water resistance needed to a degree of
certainty. Since frozen soil, like concrete, is strongest when in compression, cylindrical
shafts are the most popular shape.
Examples of deep shaft construction are SoilFreeze’s San Pedro and Harbor Island
shafts in Los Angeles, CA. Four shafts were constructed, two 14-foot diameters and
two 24-foot diameters. Each shaft was excavated to a depth of over 90 feet in beach
sand with silt layers. The shoring was designed to reach a depth of 120 to 140 feet
to provide a watertight “plug” in the bottom, taking into account the 80 feet of
hydrostatic pressure.
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