HomeMy WebLinkAboutSubsoils Report for Foundation Design1(+AKumar ni Associates, Inc.° 5020 County Road 154
Geotechnieal and Materials Engineers Glenwood Springs, CO 81601
and Environmental Scientists phone: (970) 945-7988
email: kaglenwood@kumarusa.com
www.kumarusa.com
�J An ErnployeiOvoeFtied Company
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
May 20, 2025
Roxy's Red Barn, LLC
P.O. Box 5085
Santa Barbara, CA 93150
c/o Galambos Architects
Attn: John Galambos
igalambos _.galambosarchitects.com
Project No. 25-7-326
Subject: Subsoil Study for Foundation Design, Proposed Residence, 5644 County Road
102, Garfield County, Colorado
Gentlemen:
As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations at
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the subject site. The study was conducted in accordance with our agreement for geotechnical
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engineering services to Roxy's Red Barn, LLC dated May 13, 2025. 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 located on the north side of the
ranch, just south of County Road 102, in the area shown on Figure 1. The proposed residence
will be one story over crawlspace. The attached garage will have a slab -on -grade floor. Cut
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depths are expected to range between about 2 and 6 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 proposed building site slopes at 15 to 20% grade down toward the south.
The site is vegetated with pinon pine and cedar trees with an understory of sparse grass and
weeds. Scattered basalt rocks were observed on the ground surface.
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 1 to
2 feet of stiff sandy clay with basalt fragments overlying mainly basalt rocks in a sandy clay
matrix. 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, we recommend spread footings
placed on the undisturbed natural soils below topsoil designed for an allowable soil bearing
pressure of 2,50�r support of the proposed residence. Footings should be a minimum
width of 16 inches for continuous walls and 2 feet for columns. Loose and disturbed soils
Roxy's Red Barn, LLC
May 14, 2025
Project No. 25-7-326
Page 2
encountered at the foundation bearing level within the excavation should be removed and the
footing bearing level extended down to the undisturbed natural 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 shouldnforced top and bottom to span local anomalies such as by
assuming an unsupported length of at least 10 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.
Floor Slabs: The natural on -site soils, exclusive of topsoil and oversized rock, 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 garage
slabs 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 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 and crawlspace
areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system.
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 1 % 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 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. Free -draining wall backfill (if any) should be capped with about 1 foot of
the on -site, finer graded soils to reduce surface water infiltration.
Kumar & Associates, Inc
Roxy's Red Barn, LLC Project No. 25-7-326
May 14, 2025 Page 3
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 may be
needed on the uphill side to direct surface runoff around the residence.
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.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
Kumar & ASSO
Daniel E. Ha
Rev by: SLP
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attachments Figure 1 — Location of Exploratory Pits
Figure 2 — Logs of Exploratory Pits
COUNTY ROAD 102
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APPROXIMATE SCALE —FEET
25-7-326 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
PIT 1 PIT 2 & PP-1 PP-2
EL. 6912' EL. 6910' EL. 6905'
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LEGEND
ORGANIC SANDY SILTY CLAY WITH ROOTS, MEDIUM STIFF, DARK BROWN WITH
®TOPSOIL;
SCATTERED BASALT ROCKS.
F] CLAY (CL); SILTY, SANDY WITH BASALT ROCKS, VERY STIFF, SLIGHTLY MOIST, GRAY BROWN.
BASALT ROCKS IN CLAYEY SAND AND GRAVEL MATRIX, DENSE, SLIGHTLY MOIST,
GRAY —BROWN.
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t PRACTICAL REFUSAL TO THE EXCAVATION.
.NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON MAY 14, 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 BASED ON ELEVATIONS PROVIDED BY
ARCHITECT.
4. THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS 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.
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25-7-326
Kumar &Associates
LOGS OF EXPLORATORY PITS
Fig.
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