HomeMy WebLinkAboutSubsoils Report for Foundation Designl.*n Hiffilfl..ffi:ffii'I;d**
An Employca Owncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE AND SHOP BUILDING
5473 COUNTY ROAD 320
GARFTELD COUNTY, COLORADO
PROJECT NO.25-7-246
MAY 16,2025
PREPARED F'OR:
CLAYTON HOMES
ATTN: DAVID MAHOVSKY
67123 ROAn
GRAND,TIINCTION, COT,ORADO 81 505
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david.mahovskv@ clavtonhomes.com
TABLE OF'CONTENTS
PURPOSE AND SCOPE OF STUDY.................
PROPOSED CONSTRUCTION
SITE CONDITIONS
FIELD EXPLORATION
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS .....................
FOUNDATIONS
FOUNDATION AND RETAINING WALLS
FLOOR SLABS
I.INDERDRAIN SYSTEM
SURFACE DRAINAGE................
LIMITATIONS
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURES 4 and 5 - SWELL-CONSOLIDATION TEST RESULTS
TABLE I- SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Associates, lnc. @ Project No. 25-7-246
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence and shop building to
be located at 5473 County Road 320, Garfield County, Colorado. The project site is shown on
Figure 1. The purpose of the study was to develop recommendations for the foundation design
The study was conducted in accordance with our agreement for geotechnical engineering
services to Clayton Homes dated April 2,2025.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils obtained during the field
exploration were tested in the laboratory to determine their classification, compressibility or
swell and other engineering characteristics. The results of the field exploration and laboratory
testing were analyzed to develop recommendations for foundation types, depths and allowable
pressures for the proposed building foundation. This report summarizes the data obtained during
this study and presents our conclusions, design recommendations and other geotechnical
engineering considerations based on the proposed construction and the subsurface conditions
encountered.
PROPOSED CONSTRUCTION
The proposed residence and shop building will be one-story structures located on the site
generally as shown on Figure 1. Ground floors could be structural over crawlspace or slab-on-
grade. Grading for the structure is assumed to be relatively minor with cut depths between about
2 to 4 feet. We assume relatively light foundation loadings, typical of the proposed Wpe of
construction.
If building loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The subject site was vacant at the time of our field exploration. The ground surface was gently
sloping down to the west. Vegetation consists of sagebrush, grass and weeds.
FIELD EXPLORATION
The field exploration for the project was conducted on April 30, 2025. Two exploratory borings
were drilled at the locations shown on Figure I to evaluate the subsurface conditions. The
borings were advanced with 4 inch diameter continuous flight augers powered by a truck-
mounted CME-45B drill rig. The borings were logged by a representative of Kumar &
Associates, Inc.
Kumar & Associates, lnc. o Proiect No. 25-7-246
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Samples of the subsoils were taken with a 2-inch I.D. spoon sampler. The sampler was driven
into the subsoils at various depths with blows from a 140-pound hammer falling 30 inches.
This test is similar to the standard penetration test described by ASTM Method D-1586. The
penetration resistance values are an indication of the relative density or consistency of the
subsoils. Depths at which the samples were taken and the penetration resistance values are
shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our
laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about I foot of topsoil overlying medium stiff to stiff; sandy silty clay to the
boring depth of 20 feet deep. In Boring l, a silty sand and gravel layer was encountered from
about 14 to 17 feet deep.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and finer than sand grain size gradation analyses. Results of swell-
consolidotion tcsting pcrformcd on rclativcly undisturbcd drivc samplcs of thc clay soils,
presented on Figures 4 and 5, generally indicate low to moderate compressibility under
conditions of loading and wetting. The laboratory testing is summarized in Table l.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to moist.
FOUNDATION BEARING CONDITIONS
The upper clay soils possess low bearing capacity and low to moderate settlement potential
especially when wetted. The underlying granular soil layer encountered in Boring I possesses
moderate bearing capacity but appears to be of localized extent. The proposed residence and
shop building can be founded with spread footings placed on the natural clay soils with a risk of
settlement if the bearing soils become weffed. Observing and following the recommendations in
the SURI'ACL, DRAINAGB section of this report will be critical to the long-term satisfactory
performance of the structures.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, the building can be founded with spread footings bearing on the
ttatural soils with a risk uf settlernent.
The design and construction criteria presented below should be observed for a spread footing
[ounclal.iou systern.
Kumar & Associates, lnc. @ Project No.25-7-246
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1)Footings placed on the undisturbed natural soils should be designed for an
allowable bearing pressure olllp@\ith a risk of settlement primarily if the
bearing soils become wetted. Based on experience, we expect initial settlement of
footings designed and constructed as discussed in this section will be about I inch
or less. Additional post construction settlement could occur if the bearing soils
become wetted. The magnitude of additional settlement would dcpcnd on thc
depth and extent of wetting but could be on the order of I to 1% inches.
The footings should have a minimum width of 20 inches for continuous walls and
2 feet for isolated pads.
Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
of foundations at least 36 inches below exterior grade is typically used in this
afea.
Continuous foundation walls should be heavily reinforced top and bottom to span
local anomalies and resist differential movement such as by assuming an
unsupported length of at least l4 feet. Foundation walls acting as retaining
structures should also be designed to resist lateral earth pressures as discussed in
the "Foundation and Retaining Walls" section of this report.
Topsoil and any loose disturbed soils should be removed and the footing bearing
level extended down to the relatively firm natural soils. The exposed soils in
footing area should then be moistened and compacted.
A representative ofthe geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
3)
4)
FOLINDATION AND RE,TAINING WALLS
Foundation walls and retaining structures which are laterally supported and can be expected
to undergo only a slight amount of deflection should be designed for a lateral earth pressure
computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting
of the on-site fine-grained soils. Cantilevered retaining structures which are separate from the
buildings and can be expected to deflect sufficiently to mobilize the full active earth pressure
condition should be designed for a lateral earth pressure computed on the basis of an equivalent
fluid unit weight of at least 45 pcf for backfill consisting of the on-site fine-grained soils.
Backfill can consist of the onsite soils devoid of topsoil, organics and rock larger than about
6 inches.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffrc, construction materials and equipment.
The pressures recommended above assume drained conditions behind the walls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
2)
5)
6)
Kumar & Associates, lnc. @ Project No. 25-7-246
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increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure buildup behind walls.
Backfill should be placed in uniform lifts and compacted to at least 90Yo of the maximum
standard Proctor density at a moisture content slightly above optimum. Backfill placed in
pavement and walkway areas should be compacted to at least95Yo of the maximum standard
Proctor density. Care should be taken not to overcompact the backfill or use large equipment
near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of
deep foundation wall backfill should be expected, even if the material is placed correctly, and
could result in distress to facilities constructed on the backfill.
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resistance of the footing on the foundation materials and passive earth pressure against
the side of the footing. Resistance to sliding at the boffoms of the footings can be calculated
based on a coefficient of friction of 0.30. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 300 pcf. The
coefficient of friction and passive pressure values recommended above assume ultimate soil
stlcngth. Suitable factors of safety should be included in the design to linrit the strain whir;h will
occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads should be compacted to at least 95/o of the
maximum standard Proctor densitv af e mo!sture content near ontimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade
construction. To rcducc thc cffccts of somc diffcrcntial movcmcnt, floor slabs should bc
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 CDOT Class 6 base course should be placed beneath slabs-
on-grade for support. This material should consist of minus 2-inch aggregate with at least 50%
retained on the No. 4 sieve and less than 12%o passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
on-site soils devoid of vegetation, topsoil and oversized rock.
LTNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area and where clay soils are present that local perched groundwater can develop during
Kumar & Associates, lnc. @ Project No. 25-7-246
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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 and
basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain
system. The proposed shallow crawlspace and slab-on-grade construction does not need a
foundation drain provided the finished floor level is at or above the surrounding grade.
Where provided, the drains should consist of drainpipe placed in the bottom of the wall backfill
surrounded above the invert level with free-draining granular material. The drain should be
placed at each level of excavation and at least 1 foot below lowest adjacent finish grade and
sloped at a minimum l%o to a suitable gravity outlet or sump and pump. Free-draining granular
material used in the underdrain system should contain less than 2Yo passing the No. 200 sieve,
less than 50olo passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel
backfill should be at least lYz feet deep. An impervious membrane such as 20 mil PVC should
be placed beneath the drain gravel in a trough shape and attached to the foundation wall with
mastic to prevent wetting of the bearing soils.
SURFACE DRAINAGE
Providing and maintaining proper surface drainage will be critical to the long-term satisfactory
performance of the proposed buildings. The following drainage precautions should be observed
during construction and maintained at all times after the buildings have 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 90Yo 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 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in paved areas. Free-draining wall backfill should be
covered with filter fabric and capped with about 2 feet of the on-site soils to
reduce surface water infiltration.
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 foundation walls.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this arca at this time. We make no warranty either express or implied
Kumar & Associates, Inc. o Project l{o. 25-7-246
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The conclusions and recommendations submitted in this report are based upon the data obtained
from the exploratory borings drilled at the locations indicated on Figure 1, the proposed type of
construcfion and otr experience in the area, Our services do not include dete.rmining the
presence, prevention or possibility of mold or other hiological contaminanfs (MORC) de.veloping
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 borings 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
so that 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 implernentation of our recommendations, and to veri& that the recommendations
have been appropriateiy interpreted. Significant design changes may require additionai 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.
Respectfu lly Submitted,
Kumar & Associates,
James H. Parsons,
Reviewed by:
Steven L. Pawlak, P.E.
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25-7 -246 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
LEGEND
TOPSOIL; CLAY, SILTY, SANDY, ORGANICS' FIRM, MOIST, DARK BROWN.
CLAY (CL); SILTY, SANDY, MEDIUM STIFF TO STIFF, SLIGHTLY MOIST TO MOIST, DARK BROWN,
LOW PLASTICITY.
SAND AND GRAVEL
MEDIUM DENSE, SLI
(SM-GM); SILTY, SCATTERED COBBLES, INTERLAYERED WITH SILTY SAND,
GHTLY MOIST, BROWN.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
.I.^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 8 BLOWS OF A 14o-POUND HAMMERo/ '' FALLTNG Jo TNCHES WERE REQU|RED To DRtvE THE SAMPLER 12 lNcHEs.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON APRIL 30, 2025 WITH A 4-INCH-DIAMETER
CONTINUOUS_FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OF
THE EXPLORATORY BORINGS ARE PLOTTED TO DEPTH.
4. THE EXPLORATORY BORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE
DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);
DD = DRY DENSITY (PCt) (NSTU D2216);
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D1140).
Fig. 325-7-246 Kumar & Associates LEGEND AND NOTES
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SAMPLE 0F: Sondy Cloy
IROM: tsoring 1 Gl 2'
WU = 'l 5,1 "/", UU = 6b pct
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
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Fig. 425-7-246 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS
SAMPLE OF: Sondy Cloy
FROM:Boringl@9'
WC = 1 4.8 %, DD = 100 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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25-7-246 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No.25-7-246
sAlrpl F I ocaTtoil
NATURAL
MOISTURE
CONTENT
to/"\
NATURAL
DRY
DENSITY
lbcll
GRADATION
PERCENT
PASSING NO.
200 slEvE
ATTERBERG LII,lITS UNCONFINED
COMPRESSIVE
STRETIGTI]
ab3ll
SOIL TYPEBORINGDEPTI{
aft)
GRAVEL
(%)
SAND
(%)
LIQUID LIMIT
l%l
PLASTIC
INDEX
P/"1
I 2 l5.l 86 Sandy Clay
9 14.8 100 Sandy Clay
t9 14.0 ll5 82 Sandy Clay
2 4 5.6 99 Sandy Clay
t4 14.2 110 98 Slightly Sandy Clay