HomeMy WebLinkAboutSubsoil Study for Foundation Design 09.11.20251(+AKumar & Associates, Inc.° 5020 County Road 154
Geotechnical and Materials Engineers Glenwood Springs, CO 81601
and Environmental Scientists phone: (970) 945-7988
email: kaglenwood@kumarusa.com
www.kumarusa.com
r An Employee Owned Company
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
September 111, 2025
Stueven Structures, LLC
Attn: Ryan Stueven
33 Woodruff Place
Glenwood Springs, Colorado 81601
Nan Cal stu eve n str uctu res. co m
Project No.25-7-533
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 14, Filing 8, Los
Amigos, 2647 Elk Springs Drive, Garfield County, Colorado
Dear Ryan:
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 Stueven Structures dated August 15, 2025. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered
are presented in this report. nr
Proposed Construction: Plans for the proposed residence were conceptual at the time of our
field exploration. The proposed residence is assumed to be a one- or two-story wood frame
structure with attached garage located on the site within the building envelope shown on Figure
1. Ground floors could be structural over crawlspace or slab -on -grade. Cut depths are expected
to range between about 2 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: The subject site was vacant at the time of our field exploration. The ground
surface was gently sloping down to the south/southwest in the building area with steeper slopes
at the rear of the lot away from Elk Springs Drive. Basalt boulders were visible on the ground
surface south and southwest of the building area. Vegetation consists of grass and sagebrush in
the area of the lot near Elk Springs Drive with Juniper trees away from Elk Springs Drive.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
three 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'/2 foot of topsoil, consist of nil to
2% feet of sandy clay overlying silty sandy gravel and cobbles with boulders to the maximum
explored depth of 4% feet deep. Results of swell -consolidation testing performed on a sample of
sandy clay, presented on Figure 3, indicate moderate compressibility under conditions of loading
and wetting. No free water was observed in the pits at the time of excavation and the soils were
slightly moist.
Stueven Structures, LLC Project No. 25-7-533
September 11, 2025 Page 2
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
placed on the undisturbed natural rocky soil below the clay designed for an allowable soil bearing
pressure of 2,500 psf for support of the proposed residence. The soil matrix tends to compress
after wetting and there could be some post -construction foundation settlement. Footings should
be a minimum width of 16 inches for continuous walls and 2 feet for columns. The clay 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 granular soils.
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 a lateral earth pressure based on an
equivalent fluid unit weight of at least 50 pcf for the on -site soil as backfill excluding rock larger
than 6 inches.
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 slabs -on -grade to facilitate drainage. This
material should consist of minus 2-inch aggregate with less than 50% passing 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 and where clay soils are present 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, crawlspace and basement areas, be protected from wetting and hydrostatic
pressure buildup by an underdrain system.
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 Y2% to a suitable gravity outlet. 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
Kumar & Associates, Inc
Stueven Structures, LLC Project No. 25-7-533
September 11, 2025 Page 3
sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least 1'/ feet
deep and covered with filter fabric such as Mirafi 140N or 160N.
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.
Free -draining wall backfill should be covered with filter fabric and capped with
about 2 feet of the on -site, finer graded soils to reduce surface water infiltration.
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.
4) Roof downspouts and drains should discharge well beyond the limits of all backfill.
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.
Kumar & Associates, Inc
Stueven Structures, LLC
September 11, 2025
Project No. 25-7-533
Page 4
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
Kumar & Associz
James H. Parsons
Reviewed by:
Steven L. Pawlak, P.E.
JHP/kac
Attachments Figure 1 — Location of Exploratory Pits
Figure 2 — Logs of Exploratory Pits
Figure 3 — Swell -Consolidation Test Results
Cc: Brad Jordan (brad 'ordanarchitec# maii.coni )
Kumar & Associates, Inc
ELK SPRINT ORIVE
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30 0 3❑ 60
APPROXIMATE SCALE -FEET
25-7-533 1 Kumar & Associates
LOCATION OF EXPLORATORY PITS I Fig. 1
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o d
un
O M
o M
I
in
N N
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N eq
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N N
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PIT 1
PIT 2
PIT 3
0 0
WC=8.0 — W
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DD=90
W W
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5 5 —
LEGEND
TOPSOIL; SILT, SANDY, CLAYEY, ROOTS AND ORGANICS, FIRM, SLIGHTLY MOIST, MEDIUM
BROWN.
CLAY (CL); SANDY, SILTY, STIFF, SLIGHTLY MOIST, MEDIUM BROWN.
GRAVEL (GM—ML); SILTY TO VERY SILTY, SANDY, CALCAREOUS, ANGULAR GRAVEL, DENSE,
SLIGHTLY MOIST, PALE TAN.
o•
GRAVEL AND COBBLES (GM); BOULDERS, SANDY SILT CALICHE MATRIX, DENSE, SLIGHTLY
MOIST, GRAY AND WHITE.
HAND DRIVE SAMPLE.
t PRACTICAL REFUSAL TO THE EXCAVATION.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON AUGUST 19, 2025.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPTH.
4. THE EXPLORATORY PIT LOCATIONS 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).
125-7-533 1 Kumar & Associates I LOGS OF EXPLORATORY PITS I Fig. 2 1