HomeMy WebLinkAboutLetter from Engineer - Drilled Pier Recommendations 03.10.2017H-PKUMAR
Geotechnical Engineering 1 Engineering Geology
Materials Testing 1 Environmental
5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
March 10, 2017
Nick Daley
4249 Lenox Boulevard
Venice, Florida 34293
npdalev@pcisys.net
Office Locations: Parker, Glenwood Springs, and Summit County, Colorado
Project No. 17-7-143
Subject: Drilled Pier Recommendations, Proposed Residence, Lot 24, Spring Ridge
Reserve, 43 Hidden Valley Drive, Garfield County, Colorado
Gentlemen:
As requested, we are providing drilled pier recommendations for foundation support at the
subject site. We previously conducted a subsoil study for design of foundations at the site and
presented our findings in a report dated February 3, 2017, Project No. 17-7-143.
The proposed residence is essentially the same as described in our previous report. Because of
the variable subsurface conditions encountered across the building footprint and the risk of
differential settlement and distress with a shallow spread footing, it is desired to deepen the
foundation bearing down into the bedrock. It appears about the western one-third of the building
footprint could be cut into bedrock at shallow footing bearing level. The remainder of the
foundation could be supported on drilled piers which extend down into the bedrock. Footings
placed entirely on bedrock can be sized for an allowable bearing pressure of 4,000 psf. The
remaining recommendations presented on page 4 of our previous report should be followed.
Recommendations for drilled piers are presented below. Slab -on -grade placed on non -expansive
soils or compacted structural fill should be feasible with low potentia! for movement. The
structural fill can probably consist of the onsite soils and should be further evaluated at the time
of construction.
Drilled Pier Al(ernative: Considering the subsurface conditions encountered in the exploratory
borings on the lot and the nature of the proposed construction, straight -shaft piers drilled into the
underlying bedrock can be used for building support. The design and construction criteria
presented below should be observed for a straight -shaft drilled pier foundation system.
1) The piers should be designed for an allowable end bearing pressure of 25,000 psf
and a skin friction of 2,500 psf for that portion of the pier embedded in bedrock.
Pier penetration through the upper clay soils should be neglected in the skin
friction calculations.
2) All piers should have a minimum total embedment length of 5 feet and a
minimum penetration into the bedrock of 1 foot. The bedrock appears cemented
Nick Daley
March 10, 2017
Page 2
below a thin weathered layer and practical penetration into the bedrock (without
rock bit coring) could be limited to about 2 to 4 feet.
3) The pier holes should be properly cleaned prior to placement of concrete. The
natural clay soils are stiff which indicates that casing of the holes should not be
required. Placing concrete in the pier hole the same day as drilling is
recommended.
4) The pier drilling contractor should mobilize equipment of sufficient size to
achieve the design pier sizes and depths. We recommend a minimum pier
diameter of 10 inches.
5) Grade beams and pier caps should have a minimum depth of 3 feet for frost cover
and void form below them is not needed.
6) Free water was not encountered in the borings made at the site and dewatering
should not be needed.
7) A representative of the geotechnical engineer should observe pier drilling
operations on a full-time basis.
If you have any questions or need further assistance, please call our office.
Sincerely,
H-PKUMAR
Steven L. Pawlak, P.E.
SLP/ksw
cc: Lindauer-Dunn — Jeff
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RM Construction — Blake Piland (blake@buildwithrm.com)
H -Pk KUMAR
Project No, 16-7-570