HomeMy WebLinkAboutObservation of Excavation 07.28.20151 r
July 28, 2015
Kiel Williams
33 Cardinal Lane
Glenwood Springs, Colorado 81601
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Job No. 115 335A
Subject: Observation of Excavation, Proposed Residence, Lot I5, Callicotte
Ranch, Sopris Lane, Garfield County, Colorado
Dear Mr. Williams:
As requested, a representative ofHepworth-Pawlak Geotechnical, Inc. observed the
excavation at the subject site on July 22 and 27, 2015 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 you, dated July
22, 2015.
Tlie proposed residence will be a two story wood frame structure over a crawlspace. The
attached garage will have a slab -on -grade floor. Foundations were designed for an
assumed allowable soil bearing pressure of 1,500 psf.
At the time of our initial visit to the site, the foundation excavation was underway and the
northeast comer of the house had been excavated along with a shallow pit near the
southeast building corner. The exposed soils consisted of stiff, sandy silty clay typical of
the area. Samples of the soils were taken for laboratory testing.
Upon our second visit to the site, the foundation excavation was complete and had been
cut in one level from 1 to 5 feet below the adjacent ground surface. The soils exposed in
the bottom of the excavation consisted of stiff, sandy silty clay. The clay soils in the
deeper cut areas on the north side of the house were whitish brown. Results of swell -
consolidation testing performed on samples taken from the site, shown on Figure 1,
indicate the soils have low to moderate compressibility under conditions of loading and
wetting with a minor collapse potential (settlement under constant load) when wetted.
Kiel Williams
July 28, 2015
Page 2
No free water was encountered in the excavation and the soils were slightly moist to
moist.
Considering the conditions exposed in the excavation and the nature of the proposed
construction, spread footings placed on the undisturbed natural soil designed for an
allowable soil bearing pressure of 1,500 psf can be used for support of the proposed
residence. The exposed soils tend to compress when wetted and there could be some
post -construction settlement of the foundation if the bearing soils become wet and
precautions must be taken to keep the bearing soils dry. Footings should be a minimum
width of 18 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. 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
Iength of at least 12 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 55 pcf for on-site soil as backfill. A perimeter foundation drain should be provided
to prevent temporary buildup of hydrostatic pressure behind the crawlspace walls and
prevent wetting of the crawlspace but only on the uphill side of cut depths of 4 to 5 feet.
An impervious membrane, such as 20 mil PVC should be provided below the drain gravel
in a trough shape and attached to the foundation wall with mastic to prevent wetting of
the bearing soils. Structural fill placed within floor slab areas is proposed to be "pit run"
gravel compacted to at least 95% of standard Proctor density at a moisture content near
optimum. Backfill placed around the structure should consist of the onsite soils
compacted to at least 90% of standard Proctor density at near optimum moisture content
and the surface graded at a minimum 10% 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 10 feet of the foundation.
The recommendations submitted in this letter are based on our observation of the soils
exposed within the foundation excavation 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
excavation, drilling would be required. It is possible the data obtained by subsurface
Job No. 115 335A
GeStech
Kiel Williams
July 28, 2015
Page 3
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,
HEPWORTH — PAWLAK GEOTECHNICAL, INC.
Daniel E. Hardin, P.E. ;a rt244 43
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attaclunent Figure 1— Swell -Consolidation Test Results
cc: RM Construction Blake Piland blakc(c buildwithrm.coni
Job No. 115 335A
Gecgtech
Compression 4
Compression %
0
1
2
3
4
5
6
0
1
2
3
4
5
Moisture Content = 7.7 percent
Dry Density = 97 pcf
Sample of: Sandy Silty Clay
From: Footing Grade at North Side of House
Compression
upon
wetting
0.1
1.0 10
APPLIED PRESSURE - ksf
100
0
Moisture Content = 9.3
Dry Density = 89
Sample of: Sandy Silty Clay
From: Footing Grade at Southeast Comer of
Hous@
percent
pcf
°N\\C_______ompression
upon
wetting
0.1
115 335A
1.0 10
APPUED PRESSURE - ksf
H
Hepworth—Patrlak Geotechnical
SWELL -CONSOLIDATION TEST RESULTS
100
Figure 1