Specs

Proposed Bridgestone April 20, 2011
NWC of Vance St. & W. Center Ave. PSI Project No. 532281
Lakewood, Colorado Page 7 of 15
A sample(s) of the proposed backfill soil(s) should be obtained for moisture density
relationship (proctor test) three to four days prior to backfilling operations to expedite
compaction and moisture content testing by the materials testing service provider.
Weather conditions in the site area are typically dry in the summer and early fall.
Precipitation in the form of snowfall is common from October through March. While
grading can be inhibited for short periods during and following times of precipitation,
grading can generally be conducted year round. The major factor that must be
considered during the winter months is ground freezing. During extended periods of
sub-freezing weather, it can be difficult to properly moisture condition and compact soils.
Grading must be conducted during the warmer parts of the day in freezing weather.
6.0 GEOTECHNICAL RECOMMENDATIONS
Based on the potential for vertical movement due to the high swelling soils, and the
relatively shallow depth to bedrock, it is PSI’s opinion that the proposed structure be
supported on a drilled pier foundation system and that a structurally supported floor
system be utilized. Swell mitigation through overexcavation and replacement will reduce
but not eliminate the potential for movement due to swelling soils. A drilled pier
foundation system will further reduce the potential for movement than overexcavation
and replacement could.
6.1 Drilled Pier Foundations
Piers should be sized using the allowable end-bearing pressures and side shear
resistance given below. The side shear resistance for the piers should only be
considered within the bedrock material and should be neglected in the existing
overburden material. A summary of the pier design criteria are as follows:
Allowable
End Bearing
Pressure
(psf)
Allowable
Side Shear
Resistance
(psf)
Bearing Strata
Depth of
Embedment into
Bedrock
Uplift Force
(pounds)
Hard to very hard
25,000 2,500
9 feet 106,000*
bedrock
* For 24 inch diameter pier, based on a 7 foot zone of wetting.
A minimum pier diameter of 24-inches is recommended for the piers. No shear rings or
bedrock roughening is required during drilling operations. Piers should be reinforced for
their full length. The structural engineer should size reinforcing steel for the piers based
upon the tensile forces that could be developed from the difference between the uplift force
and the dead load applied to the pier. It is recommended that the pier reinforcing steel
extend up into the grade beam, as determined by the structural engineer. A minimum 8-
inch void space should be anticipated under all grade beams, between the piers.
The calculated uplift force should be resisted by a combination of actual dead load on each
pier plus the resistance in side shear calculated for the portion of the pier in the bearing
strata, beneath the zone of wetting (7 feet below grade).
A 1/3 increase in bearing capacity may be used for wind loads of short duration. Net
tension from structural actions can be resisted using the full 2,500 psf side shear
resistance within the bedrock material.