HomeMy WebLinkAboutDrilled Pier Recommendations 01.06.2017H-P~·l<UMAR
Geolechnical Engineering I Engineering Geology
Materials Testing I Environmental
5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945·8454
Emall: hpkglanwoodC kumarusa.com
Office Locations: Parker, Glenwood Springs, and Sllverthome, Colorado
January 6, 2017
RM Construction
Attn: Blake Piland
5030 County Road 154
Glenwood Springs, Colorado 81601
blake@buildwithrm.com
Project No. 16-7-570
Subject: Drilled Pier Recommendations, Proposed Residence, Lot 30, Heron Crossing at
Ironbridge, River Bend Way, Garfield County, Colorado
Gentlemen:
As requested, we are providing drilled pier recommendations for foundation support at the
subject site. Hepworth-Pawlak Geotechnical (now H-P/Kumar) previously conducted a subsoil
study for preliminary design of foundations at the site and presented the findings in a report
dated February 8, 2016, Job No. 116 014A.
The residence is proposed to be single-story above crawlspace with slab-on-grade garage and
located in the lower, front part of the lot. The recommended settlement precaution with spread
footings was to deepen the bearing level to have no more than 6 feet of compressible, finc-
grained soils below the footings. Since the previous boring on the lot encountered about IS feet
of the fine-grained soils, deepening the footing bearing level or replacing the fine-grained soils
compacted would be needed. As an alternative to spread footings, a drilled pier foundation
which extends down into the underlying dense, gravel and cobble soil could be used with low
settlement potential.
Drilled Pier Alternative: Considering the subsoil conditions encountered in the exploratory
l;>oring on the lot and the nature of the proposed construc.tion, straight-shaft piers drilled into the
underlying gravel and cobble soils 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 10,000 psf
and a skin friction of 1,000 psf for that portion of the pier embedded in gravel.
Pier penetration through the upper silt and clay soils should be neglected in the
skin friction calculations.
2) All piers should have a minimum total embedment len8lh of 10 feet and a
minimum penetration into the gravel of 1 foot. The gravel and cobble soils will
tend to cave and penetration into the bearing soils should be limited to about 2
feet.
RM Construction
January 6, 2017
Page2
3} The pier holes should be properly cleaned prior to placement of concrete. The
natural silt and clay soils are stiff which indicates that casing of the holes should
not be required. Some caving and difficult drilling may be experienced in the
bearing soils due to cobbles and possible boulders. 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 12 inches.
5) Grade beams and pier caps should have a minimum depth of 3 feet for frost cover
and void fonn below them is not needed.
6) Free water was not encountered in the boring made at the site and dewatering
should not be needed.
7) A representative of the geotechnicaJ 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-P~KUMAR
SLP/ksw
cc:
H-P-KUMAR Project No, 1f>..7-570