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00Pilot tube microtunneling
is a variation of microtunneling where a pilot casing is installed accurately
using guided boring methods. After the pilot casing installation is complete,
a hole-enlarger is installed with an auger inside to remove the spoils.
The carrier pipe is installed behind the hole-enlarger using conventional
pipe jacking techniques. Pilot tube microtunneling is a relatively new
method that is a hybrid of directional drilling (to install the pilot
casing) and microtunneling (to install the carrier pipe). The microtunneling
design work is being completed by Jacobs Associates; GeoPentech is performing
the geotechnical investigation work.
00Geology generally consists of inter-bedded
medium dense silts, silty sands and poorly graded sands grading locally
to loose and dense. Groundwater levels range from about 30 to 47 feet
below the existing ground surface and generally below the proposed pipeline
invert except possibly locally near the western end of Segment 2 where
it was observed a few feet above the proposed pipe invert.
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