HomeMy WebLinkAboutSubsoil Study for Foundation Design Report 06.23.261(+AKunw ni Associates, Inc 5020 County Road 154
Geotechnicat and Materials Engineers Glenwood Springs, CO 81601
and Environmental Scientists phone: (970) 945-7988
email: kagienwood@kumarusa.com
www.kumarusa.com
An Employee Owned Company
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
RECEIVED
June 23, 2026
Lealon Montgomery & Jordyn Christianson
2601 County Road 233 GARFIELD COUNT
Rifle, Colorado 81650 rOMMUNITY DEVELOPMEl'
ileechristianson(aD-hotmail.com
Project No.26-7-313
Subject: Subsoil Study for Foundation Design, Proposed Residence, Across from 2601
County Road 233, Garfield County, Colorado
Dear Lealon and Jordyn:
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 May 28, 2026. 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 a single -story, wood -framed modular
structure located on the site as shown on Figure 1. Ground floor will be structural over a
crawlspace. Cut depths are expected to range between about 3 to 5 feet. Foundation loadings
for this type of construction are assumed to be relatively light and typical of the proposed type of
construction.
If building conditions 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: At the time of our field exploration, the building site was a vacant field. The
ground surface appeared natural with a slight to moderate slope sown to the south. Vegetation
consisted of grass and weeds with nearby cottonwood trees. An active irrigation ditch crosses
the property uphill of the building site. The ditch will be piped as construction on the residence
begins.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
two exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about one foot of topsoil consisted of
medium dense/stiff silty sand and clay with scattered gravel. Results of swell -consolidation
testing performed on relatively undisturbed samples of the sand and clay soils, presented on
Figures 3 and 4, indicate low compressibility under existing low moisture content and light loading
and moderate collapse potential when wetted. No free water was observed in the pits at the time
of excavation and the soils were slightly moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, spread footings placed on the
undisturbed natural soil designed for an allowable bearing pressure of 1,000 psf can be used for
support of the proposed residence with a significant risk of settlement. The soils tend to compress
after wetting and there could be post -construction foundation settlement and building distress if
the bearing soils are wetted. Footings should be a minimum width of 24 inches for continuous
Lealon Montgomery & Jordyn Christianson Project No. 26-7-313
June 23, 2026 Page 2
walls and 30 inches for columns. The topsoil and loose disturbed soils at the foundation bearing
level should be removed and the exposed soils moistened and compacted. We should observe
the completed 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 heavily reinforced top and bottom to span local anomalies such as by assuming an
unsupported length of at least 14 feet. Foundation walls acting as retaining structures should be
designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 55
pcf for the on -site soil as backfill.
Floor Slabs: The natural on -site soils, exclusive of topsoil, can be used to support lightly loaded
slab -on -grade construction with a risk of settlement. 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 of relatively well graded sand and gravel such as %-inch road base
should be placed beneath slabs for support. This material should consist of minus - inch
aggregate with less than 50% passing the No. 4 sieve and less than 12% passing the No. 200
sieve.
All fill materials for support of floor slabs should be compacted to at least 95% of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on -
site soils devoid of vegetation and topsoil.
Underdrain System: It is our understanding the proposed finished floor elevation at the lowest
level is at or above the surrounding grade. Therefore, a foundation drain system is not required.
It has been our experience in the area that local perched groundwater can develop during times
of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a
perched condition. We recommend below -grade construction, such as retaining walls, be
protected from wetting and hydrostatic pressure buildup by an underdrain and wall drain system.
A shallow crawlspace should not need to be protected with an underdrain with proper foundation
wall backfill and surface grading.
If the finished floor elevation of the proposed structure is revised to have a floor level below the
surrounding grade, we should be contacted to provide recommendations for an underdrain
system. All earth retaining structures should be properly drained.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the residence has been completed:
1) Inundation of the 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% of the maximum standard Proctor density in pavement and slab areas
and to at least 90% 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 10 feet in unpaved areas and a minimum slope of 3 inches
in the first 10 feet in pavement and walkway areas. A swale will be needed uphill
to direct surface runoff around the residence.
Kumar & Associates, Inc.®
Lealon Montgomery & Jordyn Christianson
June 23, 2026
Project No.26-7-313
Page 3
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 10
feet from the building. Consideration should be given to the use of xeriscape to
limit potential wetting of soils below the foundation 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 1 and to
the depths 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 for the exclusive use by our client for design purposes. 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 verify 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 further assistance, please let us know.
Respectfully Submitted,
Kumar & Associates, Inc.
1J
David A. Noteboom, Staff Engineer
Reviewed by:
15222
Steven L. Pawlak, P.E.
DAN/kac
Attachments Figure 1 — L �dxrploratory
oratory Pits
Figure 2 — oPits
Figures 3 & 4— Swell -Consolidation Test Results
Table 1 — Summary of Laboratory Test Results
Kumar & Associates, Inc
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1 Irrigation drainage
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approx. location of
proposed cistern
PROPERTY IS ACROSS FROM
2601 CR 233
30 0 3C 5u
APPROXIMATE SCALE -FEET
26-7-313 I Kumar & Associates I LOCATION OF EXPLORATORY PITS I Fig. 1
PIT 1 PIT 2
0 0
WC=6.3
�; DD=95
WC=2.3—200=56
Sl DD=95
w WC=3.1 w
w
DD=107
= 5—200=16 5
WC=3.7 w
o DD=94
L10 10
LEGEND
TOPSOIL; SANDY SILT AND CLAY WITH ORGANICS, FIRM, SLIGHTLY MOIST TO MOIST, DARK
BROWN.
SAND AND CLAY (SC—CL) SILTY, SCATTERED GRAVEL TO GRAVELLY LAYERS, MEDIUM
DENSE/STIFF, SLIGHTLY MOIST, BROWN, SLIGHTLY POROUS.
HAND DRIVEN 2—INCH DIAMETER LINER SAMPLE.
NOTES
3 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JUNE 12, 2026.
04
c 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
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i 3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPTH.
0 4. THE EXPLORATORY PIT LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE
M IMPLIED BY THE METHOD USED.
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5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE
N APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
i
N 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE
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BACKFILLED SUBSEQUENT TO SAMPLING.
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7. LABORATORY TEST RESULTS:
i WC = WATER CONTENT (%) (ASTM D 2216);
o DD = DRY DENSITY (pcf) (ASTM D 2216);
M w —200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
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26-7-313 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
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SAMPLE OF: Very Sandy Silty Clay
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26-7-313
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SWELL —CONSOLIDATION TEST RESULTS
Fig. 3
SAMPLE OF: Sandy Silty Clay
FROM: Pit 2 ® 6'
WC = 3.7 %, DD = 94 pcf
2
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26-7-313
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SWELL —CONSOLIDATION TEST RESULTS
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