HomeMy WebLinkAboutSubsoils Report for Foundation DesignI (tA fliffilffi*l:lt:fr'""sd'
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An Employcc Owncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenrvood@kumarusa.com
rvlvrv. kutn arusa. com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs. and Sununit County, Colorado
April2,2025
Kyle Byman
213 County Road 228
Silt, Colorado 81652
k),lebvrnan@ icloud.corn .'
Project No.24-7-709
Subject: Subsoil Study for Foundation Design, Proposed Residence, 213 County Road
228, Garfreld County, Colorado
Dear Mr. Byman:
As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations at
the subject site. The study was conducted in accordance with our agreement for geotechnical
engineering services to you dated December 26, 2024. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: The proposed residence will be approximately 30 feet by 96 feet in
size with the long axis of the building in the east-west direction located as shown on Figure l.
Ground floor will be slab-on-grade in the garage and above crawlspace in the living room. Cut
depths are expected to range between about2 to 5 feet. Foundation loadings for this type of
construction are assumed to be relatively light and typicalof the proposed type of construction.
If building location, construction type or foundation loadings are significantly different from
those described above, we should be notified to re-evaluate the recommendations presented
in this report.
Site Conditions: The property is cunently developed with an existing residence and several
outbuildings. The property slopes down to the south-southwest at grades of 5oh to 8% in the
proposed building area. The proposed building area is vegetated with grass.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
two exploratory pits at the approximate locations shown on Figure l. The logs of the pits are
presented on Figure 2. The subsoils encountered, below aboutVz to I foot of topsoil, typically
consist of sandy silt and clay down to the maximum depth explored of 8 feet. The subsoils were
more sandy and with gravel and scaffered cobbles in Pit 1. Results of swell-consolidation testing
performed on relatively undisturbed samples of sandy silty clay, presented on Figures 3 through
5, indicate low compressibility under existing moisture conditions and light loading and
moderate compressibility potential under increased loading after wetting. No free water was
observed in the pits at the time of excavation and the subsoils were moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
N
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s
.,
placed on the undisturbed natural soil designed for an allowable bearing pressure of 1,500 psf for
support of the proposed building. The soils tend to compress under loading and when wetted and
we expect that there will be some sefflement as the building loads are applied. Footings should
be a minimum width of 18 inches for continuous walls and 2 feet for columns. The topsoil and
loose disturbed soils encountered at the foundation bearing level within the excavation should be
removed and the footing bearing level extended down to the undisturbed natural soils. We
should observe the completed foundation excavation for bearing conditions. Exterior footings
should be provided with adequate cover above their bearing elevations for frost protection.
Placement of footings at least 36 inches below the exterior grade is typically used in this area.
Continuous foundation walls should be reinforced top and bottom to span local anomalies such
as by assuming an unsupported length of at least 12 feet. Foundation walls acting as retaining
structures (should be designed to resist alateral earth pressure based on an equivalent fluid unit
weight of at least 50 pcf for the on-site soil as backfill. A foundation drain is not needed for the
relatively shallow crawlspace depth.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded
slab-on-grade construction. To reduce the effects of some differential movement, floor slabs
should be separated from all bearing walls and columns with expansion joints which allow
unrestrained vertical movement. Floor slab control joints should be used to reduce damage due
to shrinkage cracking. The requirements for joint spacing and slab reinforcement should be
established by the designer based on experience and the intended slab use. A minimum 4 inch
layer ofroad base gravel should be placed beneath slabs-on-grade to provide support.
All fill materials for support of floor slabs should be compacted to at least 95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of
properly placed and compacted on-site soils devoid of vegetation, topsoil and oversized rock.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the building has been completed:
1) Inundation ofthe foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95%o of the maximum standard Proctor density in pavement and slab areas
and to at least 90o/o of the maximum standard Proctor density in landscape areas.
3) The ground surface surrounding the exterior of the building should be sloped to
drain away from the foundation in all directions. We recommend a minimum
slope of 12 inches in the first l0 fcct in unpavcd arcas and a minimum slopc of
3 inches in the first 10 feet in pavement and walkway areas. A swale may be
needed uphill to direct surface runoff around the building.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation should be located at least
l0 feet from foundation walls. Consideration should be given to the use of
Kumar & Associates, lnc. @ Project No. 24-7-709
J.
xeriscape to limit potential wetting of soils below the building caused by
irrigation.
Limitations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this area at this time. We make no warranty either
express or implied. The conclusions and recommendations submitted in this report are based
upon the data obtained from the exploratory pits excavated at the locations indicated on Figure I
and to the deplhs shown on Figure 2, the proposed type of construction, and our experience in
the area. 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. Our
findings include interpolation and extrapolation of the subsurface conditions identified at the
exploratory pits and variations in the subsurface conditions may not become evident until
excavation is performed. If conditions encountered during construction appear different from
those described in this report. we should be notified at once so re-evaluation of the
recommendations may be made.
This report has been prepared fbr the exclusive use by our client for design pulposes. We are
not responsible for technical interpretations by others of our information. As the project evolves,
we should provide continued consultation and field services during construction to review and
monitor the implementation of our recommendations, and to veri$r that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recommendations presented herein. We recommend on-site observation
of excavations and foundation bearing strata and testing of structural fill by a representative of
the geotechnical engineer.
If you have any questions or if we may be of fuither assistance, please let us know.
Respectfully Submitted,
Kumar & Associates, lnc.
Daniel E. Hardin, P.E.
Reviewed by
Steven L. Pawlak,
DEH/kac
attachments Figure 1 *Exploratory Pits
Figure 2 *Logs of Exploratory Pits
Figure 3 through 5 - Swell-Consolidation Test Results
Table 1 * Summary of Laboratory Test Results
a 15222
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24-7 -709 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
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PIT 1
EL. 5742'
PIT 2
EL. 5749'
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DD=94
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LEGEND
TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, MOIST, BROWN
CLAY AND SILT (CL-ML); SANDY, STIFF, MOIST, BROWN
SAND AND SILT (SM-ML); GRAVEL, SCATTERED COBBLES, MEDIUM DENSE, MOIST, BROWN
F
HAND DRIVEN 2_INCH DIAMETER LINER SAMPLE
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON MARCH 12,2025.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY
TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
wC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (PCf) (ASTM D 2216);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1 1 4o).
LOGS OF EXPLORATORY PITS Fig. 224-7 -709 Kumar & Associates
SAMPLE OF: Sondy Silty Cloy
FROM: Pit 1 @ 1.5'
WC=21 .5%,DD =91 pcf
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ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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24-7 -709 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 5
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SAMPLE OF: Sondy Cloy ond Silt
FROM:Pit2@3'
WC = 1 4.7 %, DD = 104 pcf
NO MOVEMENT UPON
WETTING
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24-7 -709 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
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SAMPLE OF: Sondy Cloy ond Silt
FROM:Pit2@6'
WC = 17.4 %, DD = 94 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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24-7 -709 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5
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TABLE 1
SUMMARY OF LABOMTORY TEST RESULTS
Project N0.24.7-709
NATURAL
MOISTURE
CONTENT
to/"\
NATURAL
DRY
DENSITY
lDcll
GRADATION
PERCENT
PASSING NO.
200 stEVE
ATI LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
losfl
SOIL TYPEPITDEPTH
tfil
GRAVEL
(%l
SAND
(%)
LIOUID LIMIT
lo/^r
PLASTIC
INDEX
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l l%21.5 9l Sandy Silty Clay
4 14.5 98 48 Very Silty Sand
6 15.9 104 54 Very Sandy Silt
2 J 14.7 104 Sandy Clay and Silt
6 17.4 94 Sandy Clay and Silt