HomeMy WebLinkAboutSubsoils Report for Foundation DesignKumar & Associates, Inc."
141 Geotechnical and Materials Engineers 5020 County Road 154
and Environmental 5cienlists Glenwood Springs, CO 81601
phone: (970) 945-7988
--��. email: kaglenwood@kumarusa.com
An Employee Owned Company www.kumarusa.com
Office Locations: Denver (Fitz). Parker. Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED SHOP BUILDING
LOT 1, BOOMS PLACE SUBDIVISION
22 BOOMS PLACE
GARFIELD COUNTY, COLORADO
PROJECT NO. 25-7-663
DECEMBER 19, 2025
PREPARED FOR:
GONZALO BAUTISTA MENDOZA
22 BOOMS PLACE
RIFLE, COLORADO 81650
men dozafinishcar ent l IcAn mail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY ................................ - -
PROPOSED CONSTRUCTION........................................................•--......:.............
SITECONDITIONS........................................................................•---•--................-----.------..._... 1 -
FIELD EXPLORATION .................................. ............._....................... 1 -
SUBSURFACE CONDITIONS _ 2-
FOUNDATION BEARING CONDITIONS.............................................................................- 2-
DESIGN RECOMMENDATIONS...................................................
FOUNDATIONS _ 2-
FOUNDATION AND RETAINING WALLS ....... ............................................:....................
. 3 -
FLOORSLABS ............................ .................... ...........- 4 -
UNDERDRAIN SYSTEM.............••-..............................._................... ,..._...- 4 -
SURFACEDRAINAGE ................ ........ ....................................................... ........................ .4 -
LIMITATIONS...........................................................................................................................- 4 -
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2 - LOG OF EXPLORATORY BORING
FIGURES 3 and 4 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. ® Project No. 25-7-663
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed shop building to be located on
Lot 1, Booms Place Subdivision, 22 Booms Place, 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 Gonzalo Bautista Mendoza dated October 29, 2025.
An exploratory boring was drilled to obtain information on the subsurface conditions. Samples of
the subsoils and bedrock 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 shop building will be a single -story steel -frame metal -skin structure with a footprint
of approximately 80x40 feet. Ground floor will be slab -on -grade. Grading for the structure is
assumed to be relatively minor with cut depths between about 3 to 5 feet. We assume relatively
light to moderate foundation loadings, typical of the proposed type 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 a vacant field south of, and below, the exisitng residence. The ground
surface was gently sloping down to the south at a grade of less than 5 percent. The existing
residence is a single story structure over a walkout basement level. Vegetation consists of grass
and weeds. Based on cursory field observations and conversations with the client, the existing
residence is in good condition from a foundation viewpoint.
FIELD EXPLORATION
The field exploration for the project was conducted on November 13, 2025. One exploratory
boring was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The
boring was advanced with 4-inch diameter continuous flight augers powered by a truck -mounted
CME-45B drill rig. The boring was logged by a representative of Kumar & Associates, Inc.
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 and hardness of the bedrock. Depths at which the samples were taken and the
penetration resistance values are shown on the Log of Exploratory Boring, Figure 2. The samples
were returned to our laboratory for review by the project engineer and testing.
Kumar & Associates, Inc. 11 Project No. 25-7-663
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SUBSURFACE CONDITIONS
A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The
subsoils consist of about 1 foot of topsoil overlying stiff to very stiff, sandy clay to a depth of 18
feet where weathered claystone was encountered, becoming harder down to the drilled depth of
25 feet.
Laboratory testing performed on samples obtained from the boring included natural moisture
content and density and finer than sand grain size gradation analyses. Results of swell -
consolidation testing performed on relatively undisturbed drive samples of the clay soils,
presented on Figure 3, indicate low to moderate compressibility under conditions of loading and
wetting. Results of swell -consolidation testing performed on a relatively undisturbed drive sample
of the weathered claystone, presented on Figure 4, indicate low compressibility under existing
moisture conditions and loading and a minor settlement potential to moderate expansion potential
when wetted under constant light surcharge load. The laboratory testing is summarized in Table
1.
No free water was encountered in the boring at the time of drilling, and the subsurface materials
were slightly moist to moist.
FOUNDATION BEARING CONDITIONS
The clay soils encountered in the boring possess low bearing capacity and low settlement
potential, primarily when wetted. The deeper claystone encountered in the borings possess
moderate bearing capacity and low to moderate expansion potential when wetted. At assumed
excavation depths, we expect the foundation to bear on the clay soils. The proposed shop
building can be supported on spread footings bearing on the clay soils with a risk of foundation
settlement if the bearing soils become wet.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the natural soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils should be designed for an
allowable bearing pressure of 1,500 psf. Based on experience, we expect initial
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less. Additional long-term settlement could occur if the bearing
soils become wetted. The magnitude of additional settlement would depend on
the depth and extent of wetting but could be on the order of 1 inch.
2) The footings should have a minimum width of 20 inches for continuous walls and
2 feet for isolated pads.
3) 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 area.
Kumar & Associates, Inc. ® Project No. 25-7-663
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4) Continuous foundation walls should be well 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 also be designed to resist
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this report.
5) 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.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOUNDATION AND RETAINING 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 soils. Cantilevered retaining structures which are separate from the shop 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 soils. Foundation backfill can consist of the on -
site soils devoid of topsoil, organics and rock larger than about 5 inches.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, 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
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 90% 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 least 95% 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 bottoms 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 350 pcf. The coefficient of
friction and passive pressure values recommended above assume ultimate soil strength. Suitable
factors of safety should be included in the design to limit the strain which 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% of the maximum standard Proctor
density at a moisture content near optimum.
Kumar & Associates, Inc. ® Project No. 25-7-663
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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 forjoint 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 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% 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, topsoil and oversized rock.
UNDERDRAIN SYSTEM
The proposed shallow foundations should not need a perimeter foundation drain, provided that
the exterior foundation wall backfill is well -compacted and good surface drainage, as described
below, is maintained around the shop building.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at
all times after the shop 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 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 5
feet from foundation walls. Consideration should be given to use of xeriscape to
reduce the potential for 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 boring drilled at the location indicated on Figure 1, the proposed type of
construction and our experience in the area. Our services do not include determining the
Kumar & Associates, Inc. 11 Project No. 25-7-663
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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 boring 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 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.
Respectfully Submitted,
Kumar & Associates, Inc.
9ZM40'-' M r
James H. Parsons, P.E.
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Kumar & Associates, Inc. 8 Project No. 25-7-663
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BORING 1
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TOPSOIL; CLAY, SANDY, ORGANICS, FIRM, BROWN, SLIGHTLY
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MOIST.
CLAY (CL); SANDY, SCATTERED SAND LAYERS, STIFF TO VERY
9/12
STIFF, MOIST, BROWN.
WC=13.5
DD=107
CLAYSTONE BEDROCK, WEATHERED TO HARD, SLIGHTLY MOIST TO
8/12
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MOIST, TAN AND GRAY.
WC=15.6
DD=113
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
9/12
DRIVE SAMPLE BLOW COUNT. INDICATES THAT 9 BLOWS OF
A 140--POUND HAMMER FALLING 30 INCHES WERE REQUIRED
16/12
TO DRIVE THE SAMPLER 12 INCHES.
WC=11.1
DD=116
NOTES
1.
THE EXPLORATORY BORING WAS DRILLED ON NOVEMBER 13, 2025
18/12
WITH A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER.
2.
THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED
APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE
PLAN PROVIDED.
3.
THE ELEVATION OF THE EXPLORATORY BORING WAS OBTAINED
46/12
BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN
WC=13.4
PROVIDED.
DD=119
4.
THE EXPLORATORY BORING LOCATION AND ELEVATION SHOULD BE
—200=77
CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE
METHOD USED.
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5.
THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY
50/5
BORING LOG REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN
MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6.
GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE
TIME OF DRILLING.
7.
LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DO = DRY DENSITY (pcf) (ASTM D 2216);
—200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
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