HomeMy WebLinkAbout180829 Shapiro Soils Report.pdf mAR5020 County Road 154
Glenwood Springs, CO 81601
Geotechnical Engineering I Engineering Geology Phone:(970)945-7988
Materials Testing I Environmental Fax: (970)945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Denver(HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County,Colorado
August 29, 2018
Cohen Construction, Inc.
Attn: Jeff Cohen
P. O. Box 1889
Edwards, Colorado 81632
jcohen@cohenconstructioninc.com
Project No. 18-7-533
Subject: Observation of Excavation, Proposed Addition to Shapiro Residence,4425 Glen
Falls Lane, Vail, Colorado
Dear Jeff:
As requested, a representative of H-P/Kumar observed the excavation at the subject site on
August 28, 2018 to evaluate the soils exposed for foundation support. The findings of our
observations and recommendations for the foundation design are presented in this report. The
services were performed in accordance with our agreement for professional engineering services
to Cohen Construction, Inc. dated August 23, 2018.
The addition will be a bump out attached to the southeast side of the residence. The addition will
be two-story wood frame construction over crawlspace. There will also be two nearby footing
pads to the east for support of a deck addition. The additions have been designed to be supported
on spread footings assuming an allowable soil bearing pressure of 2,000 psf. The existing
residence is apparently founded on shallow spread footings.
At the time of our site visit, the foundation excavation for the addition and the two footing pads
had each been cut in one level from about 4 to 5 feet below the adjacent ground surface. The
excavation subgrade was at to about 2 feet below the existing building spread footing bearing
level. The soils exposed in the bottom of the excavations consisted of relatively dense, silty
clayey sand and gravel with cobbles. The soils were too rocky to obtain an undisturbed sample
for swell-consolidation testing. The results of a gradation analysis performed on a disturbed bulk
sample of the sand and gravel soils (minus 3-inch fraction) obtained from the site are presented
on Figure 1. No free water was encountered in the excavations and the soils were generally
moist.
Considering the conditions exposed in the excavations and the nature of the proposed
construction, spread footings placed on the undisturbed natural granular soil designed for an
allowable bearing pressure of 2,000 psf can be used for support of the proposed additions. There
could be some settlement of the addition foundations with respect to the existing structure which
Cohen Construction, Inc.
August 29, 2018
Page 2
should be considered in the design. Footings should be a minimum width of 16 inches for
continuous walls and 2 feet for columns. Loose and disturbed soils in footing areas should be
removed and the bearing level extended down to the undisturbed natural soils, and the subgrade
compacted. Exterior footings should be provided with adequate soil cover above their bearing
elevations for frost protection. Continuous foundation walls should be reinforced top and bottom
to span local anomalies such as by assuming an unsupported length of at least 10 feet.
Foundation walls acting as retaining structures should also be designed to resist a lateral earth
pressure based on an equivalent fluid unit weight of at least 50 pcf for on-site sand and gravel
soil as backfill. A perimeter foundation drain should be provided to prevent temporary buildup
of hydrostatic pressure behind the foundation walls and prevent wetting of the crawlspace.
Backfill placed around the structure should be compacted to at least 90% (95% in pavement
areas) of standard Proctor density and the surface graded to prevent ponding within at least
10 feet of the building. Landscape that requires regular heavy irrigation, such as sod, and
sprinkler heads should not be located within 5 feet of the foundation.
The recommendations submitted in this letter are based on our observation of the soils exposed
within the foundation excavations and do not include subsurface exploration to evaluate the
subsurface conditions within the loaded depth of foundation influence. This study is based on
the assumption that soils beneath the footings have equal or better support than those exposed.
The risk of foundation movement may be greater than indicated in this report because of possible
variations in the subsurface conditions. In order to reveal the nature and extent of variations in
the subsurface conditions below the excavations, drilling would be required. It is possible the
data obtained by subsurface exploration could change the recommendations contained in this
letter. Our services do not include determining the presence, prevention or possibility of mold or
other biological contaminants (MOBC) developing in the future. If the client is concerned about
MOBC, then a professional in this special field of practice should be consulted.
If you have any questions or need further assistance, please call our office.
Sincerely,
H—PI KU a .�`� ° �sj'�•
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David A. Young, P � 191 •
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attachment Figure 1, Gradation Test Results
cc: Cohen Construction—Kathy Fagan (admin@cohenconstructioninc.com)
H-PWUMAR
Project No. 18-7-533