HomeMy WebLinkAboutSubsoils Report for Foundation DesignKumar & Associates, Inc. °
K Geotechnical and Materials Engineers 5020 County Road 154
and Environmental Scientists Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employee Owned Company 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
LOT 33, RAPIDS ON THE COLORADO
RAPIDS VIEW LANE
GARFIELD COUNTY, COLORADO
PROJECT NO.25-7-359
AUGUST 11, 2025
PREPARED FOR:
JUSTIN SANFORD
200 MOUNTAIN SHADOWS DRIVE
GLENWOOD SPRINGS, COLORADO 81601
iustin@ifo-rentals.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY........................................................................................ 1
PROPOSEDCONSTRUCTION................................................................................................. 1
SITECONDITIONS...................................................................................................................- 1
FIELDEXPLORATION............................................................................................................- 1 -
SUBSURFACECONDITIONS.................................................................................................. 2-
FOUNDATION BEARING CONDITIONS.............................................................................. - 2-
DESIGN RECOMMENDATIONS............................................................................................. 2-
FOUNDATIONS.......................................................................................................... 2-
FOUNDATION AND RETAINING WALLS....................................................................... - 3-
FLOORSLABS............................................................................. 4 -
UNDERDRAINSYSTEM..................................................................................................... 4-
SURFACEDRAINAGE......................................................................................................... - 5
LIMITATIONS.....................................................
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
................... .- 5 -
Kumar & Associates, Inc. 0 Project No. 25-7-359
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
33, Rapids on the Colorado, Rapids View Lane, 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 Justin Sanford dated May 20, 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
Plans for the proposed residence were conceptual at the time of our study. The proposed
residence is generally planned to be a single -story structure with an attached garage. 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 6 feet. We assume relatively light
foundation loadings, typical of the proposed type of construction.
If building location, grading or loading information is significantly different than described
above, we should be notified to re-evaluate the recommendations presented in this report.
SITE CONDITIONS
The subject site was vacant at the time of our field exploration. The ground surface was
realatively flat and gently sloping down to the northwest toward the Colorado River. Vegetation
consists of grass and weeds.
FIELD EXPLORATION
The field exploration for the project was conducted on June 25, 2025. Two exploratory borings
were drilled at the locations shown on Figure 1 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.
Samples of the subsoils were taken with 1%-inch and 2-inch I.D. spoon samplers. The samplers
were driven into the subsoils at various depths with blows from a 140-pound hammer falling 30
Kumar & Associates, Inc. 0 Project No. 25-7-359
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inches. This testis 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 encountered below about %2 foot of topsoil consist of about 2 to 4 feet of stiff, sandy
silty clay above silty sand with gravel to about 3'/z to 5'/z feet deep overlying relatively dense,
silty sandy gravel and cobbles to the maximum drilled depth of 13% feet. Drilling in the coarse
granular soils with auger equipment was difficult due to the cobbles and probable boulders and
drilling refusal was encountered in the deposit.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and finer than sand size gradation analyses. Results of swell -consolidation
testing performed on a relatively undisturbed drive sample of the clay soil, presented on Figure
4, indicate initial low compressibility under light loading and moderate compressibility under
conditions of loading and wetting. The laboratory testing is summarized in Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to moist with depth.
FOUNDATION BEARING CONDITIONS
The upper clay soils encountered in the borings possess low bearing capacity and low to
moderate settlement potential especially when wetted under load. The underlying granular soils
possess moderate bearing capacity and typically low settlement potential. At assumed excavation
depths, we expect the exposed subsoils to transition between clay and granular (sand and gravel)
soils. The proposed residence can be supported on spread footings bearing on the natural
granular soils. Clay soils exposed at foundation bearing level should be removed and the bearing
level lowered to the granular soils or replaced with compacted structural fill.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the natural granular soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 2,000 psf Based on experience, we expect
�.4
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settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less. The settlement risk can be limited by extending the
bearing level completely down to the dense gravel.
2) The footings should have a minimum width of 18 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.
4) Continuous foundation walls should be well reinforced top and bottom to span
local anomalies and resist differential movement 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, clay and any loose disturbed soils should be removed and the footing
bearing level extended down to the natural granular soils. The exposed sand soils
in footing areas should then be moisture conditioned and compacted. Structural
fill placed to reestablish design bearing level can consist of the onsite granular
soils compacted to at least 98% of standard Proctor density at near optimum
moisture content. The fill should extend beyond the footing edges a distance
equal to at least one-half the depth of fill below the footing.
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 50 pcf for backfill consisting
of the on -site soils. Cantilevered retaining structures which are separate from the residence 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 40 pcf for backfill consisting of the on -site soils. Backfill should not contain organics
or rock larger than about 6 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.
Kumar & Associates, Inc. 0 Project No. 25-7-359
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Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at a moisture content near 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 0.35. 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.
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 of free -
draining gravel should be placed beneath basement level slabs (if provided) to facilitate drainage.
This material should consist of minus 2-inch aggregate with at least 50% retained on the No. 4
sieve and less than 2% 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
Although free water was not encountered during our exploration, it has been our experience in
the area that the groundwater level can rise and 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,
crawlspace areas deeper than 4 feet and basement areas (if any), be protected from wetting and
hydrostatic pressure buildup by an underdrain system.
Kumar & Associates, Inc. 0 Project No. 25-7-359
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The drains should consist of rigid perforated PVC 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 ''/2% to a suitable gravity outlet or drywell. Free -draining granular material
used in the underdrain system should contain less than 2% passing the No. 200 sieve, less than
50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill
should be at least 1'/2 feet deep.
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 6 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
10 feet from foundation walls.
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 borings drilled at the locations indicated on Figure 1, 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 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.
Kumar & Associates, Inc." Project No. 25-7-359
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.
L
Steven L. Pawlak, P.
Reviewed by: •'� ��
Daniel E. Hardin, P.E.
SLP/kac
Cc: Jordan Architecture — Brad Jordan(bradjordanarchitect(a_-.gmail.con-i)
Kumar & Associates, Inc. 0 Project No. 25-7-359
Edge of chip/seal
JRAPIDSW
VIEW' Found 1-1/2" aluminum cap and
a.LANE rebar set flush with grade, PLS
No. 13501
ie riser +�`�. �� 65 / 200' ISDS setback from
domestic well located
side S nai aon Lot 30.
h � � �
/ p -Curb stop
1Fet nai lath
N'
./2" aluminum cap
flush with grade,
20' and 10' Utility, Drainages
and Irrigation easements
the Rapids on the ColoradgSubd� _
Outline of building setbacks
\� as per the final plat: c# the ��
\ Rapids on the Colora�o Subd. _
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Domestic well Lot 30
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BORING 1 \Fn-1/2" aluminum c,
set 011ush with grade
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et flush with grade, PLS
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rebar set flush with grade, PLS aA COAAO�
No. 13501
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APPROXIMATE SCALE —FEET
25-7-359 1 Kumar & Associates
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Road
LOCATION OF EXPLORATORY BORINGS I Fig. 1
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LEGEND
TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, SLIGHTLY MOIST, DARK BROWN.
CLAY (CL); SILTY, SANDY, STIFF, SLIGHTLY MOIST, BROWN, LOW PLASTICITY.
SAND (SM); SILTY, SCATTERED GRAVEL, MEDIUM DENSE, SLIGHTLY MOIST, BROWN.
GRAVEL AND COBBLES (GM); SILTY, SANDY, PROBABLE BOULDERS, MEDIUM DENSE TO DENSE,
SLIGHTLY MOIST TO MOIST WITH DEPTH.
hDRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
I
DRIVE SAMPLE, 1 3/8-INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST.
DISTURBED BULK SAMPLE.
25/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 25 BLOWS OF A 140-POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO ❑RIVE THE SAMPLER 12 INCHES.
DEPTH AT WHICH BORING CAVED.
t PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON JUNE 25, 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 (pcf) (ASTM D2216);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140).
25-7-359 1 Kumar & Associates
LEGEND AND NOTES
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