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project's construction manager, project architect, project structural engineer, and a pile
installation contractor, we judge that an auger -cast pile foundation is appropriate for the
proposed Fry's Electronics Superstore. Provided the pile foundation is designed and installed in
accordance with the recommendations in this report, we estimate total settlement will be less
than %z inch. Differential settlement between piles should be less than '/. inch.
We initially evaluated incorporating a shallow spread footing or mat foundation (up to 3 to 4 feet
thick) for supporting the proposed superstore. However, our investigation encountered the
presence of a shallow peat layer that is approximately 10 to 17 feet bgs. This peat layer varies
from I to 7 feet thick. We estimated that total settlement ranges from 1 to 2 inches with
differential settlement varying from %i to 1 inch. Discussions with the design team indicated that
this amount of total and differential settlement was not acceptable. Consequently, shallow
spread footing or mat foundations were eliminated as potential foundation alternatives.
We subsequently evaluated piles for supporting the proposed Fry's superstore. Our investigation
also encountered a second deeper peat layer that is approximately 5 feet thick and located about
35 to 40 feet bgs. This layer is also settlement sensitive. We estimated that a pile foundation
that is terminated above this unit would have total and differential settlements of 1 to 2 inches
and I,- to i inch, respectively. This amount of settlement is also unacceptable to the design team.
Consequently, a pile foundation, would have to be embedded into the underlying Post -Glacial
Alluvial Sand layer where total and differential settlements are estimated at %z and '/. inch,
respectively.
During our March 13 meeting, we evaluated three types of piles including drilled piles (auger -
cast) and driven piles (timber and steel). The Post -Glacial Alluvial Sand layer (which would be
our target bearing zone) varies in depth from about 50 to 64 feet bgs. Therefore, the pile type
used at this site should be flexible in adjusting the pile length with minimal waste. Given the
variability of the Post -Glacial Alluvial Sand layer, there is a good potential for a considerable
amount of waste material in usine a timber or steel driven pile. Consequently, auger -cast piles
are recommended for this site given that the pile length car. be adjusted for existing site
conditions. Auger -cast piles are commonly installed in the Pacific Northwest. Local pile driving
contractors indicate that auger-cac -tiles can be installed for roughly $20.00 per linear foot
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