HomeMy WebLinkAboutSubsoils Report for Foundation DesignlGrtfliffilflffifffin$:'i**
An Emdoyca Orncd 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 f,ocations: Denver (HQ), Parter, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
July 29,2024
Bramco, LLC
Attn: Brad Mollman
105 Mid Valley Drive
New Castle, Colorado 81647
brad@bramcollc.com
24-7-395
Subject: Subsoil Study for Foundation Design, Proposed Pole Barn/ADU, Riverview
Ranch, 563 County Road 335, Silt, Colorado
Dear Mr. Mollman:
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 you dated July 8, 2024. The data obtained and our recommendations
based on the proposed construction and subsurface conditions encountered are presented in this
report.
Proposed Construction: The proposed pole barn/ADU will be a tall, one-story, wood frame
structure located on the site in the area of the pits shown on Figure 1. Ground floor will be slab-
on-grade. Cut depths are expected to range between about 2%to 4 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 recolnmendations presented in this report.
Site Conditions: The site is a relatively flat grass meadow with a slight slope down to the north.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
four exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. The subsoils encountered, below up to about 1 foot of topsoil, consist of
medium stiff to stiff sandy silt and clay. Results of swell-consolidation testing performed on
relatively undisturbed samples of the clay subsoils, presented on Figures 3 and 4, indicate low
compressibility under existing moisture conditions and light loading and a low collapse
(settlement under constant load) potential when wetted. The samples were moderately to highly
compressible under increased loading after wetting. No free water was observed in the pits at
the time of excavation and the soils were slightly'moist to moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
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placed on the undisturbed natural soil designed for an allowable bearing pressure of 1,500 psf
for support of the proposed pole bam/ADU. The soils tend to compress after wetting and there
could be some post-construction foundation settlement if the bearing soils become wet. Footings
should be a minimum width of I 8 inches for continuous walls and 2 feet for columns. Loose
and 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 soils. We
should observe the completed foundation excavation for bearing conditions. 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 (if any) should be designed to resist alateral earth pressure based on an equivalent
fluid unit weight of at least 55 pcf for the on-site soil as backfill.
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 the slabs to act as a leveling course and
facilitate drainage. This material should consist of minus 2 inch aggregate with less than50%o
passing the No. 4 sieve and less than2Yo passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95o/o of maximum
standard Proctor density at a moisture content near optimum. Required filI can consist of the
on-site soils devoid of vegetation, topsoil and oversized rock.
Underdrain System: A perimeter drain system should not be needed for the proposed slab-on-
grade floor.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the pole barnlADU 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 95Yo of thc 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 pavement and walkway areas.
Kumar & Associates, lnc. @ Project No, 24-7-395
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4) Roof downspouts and drains (if any) should discharge well beyond the limits of
all backfill.
5) Landscaping which requires regular heavy irrigation should be located at least
5 feet from the building. Consideration should be given to the use of xeriscape to
limit potential wetting of soils below the foundation 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 pits excavated at the locations indicated on Figure 1
and to the depths shown on Figure 2,theproposed 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 exhapolation 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
recoflrmendations may be made.
This report has been prepared for the exclusive use by our client for design putposes. 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 veriry 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 geotechnicai engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
Kumar & Associates,lne.
Daniel E. Hardin, P.
Rev. by: SLP
DEH/kac
attachments Figure 1 - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figures 3 and 4 - Swell-Consolidation Test Results
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Kumar & Associates, lnc.6 Proiect No. 24-7-395
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24-7 -395 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
PIT 1 PIT 2 PIT 5 PIT 4
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WC=7.5
DD=1 00 WC=7.6
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TOPSOIL; ORGANIC CLAYEY SILT, SANDY, SOFT, SLIGHTLY MOIST, LIGHT BROWN.
POSSIBLE FILL; SANDY SILTY CLAY WITH ROCKS (PlT 1 ONLY).
SILT AND CLAY (CL-ML); SANDY TO SILTY CLAYEY SAND WITH SCATTERED COBBLES AND
GRAVEL, MEDIUM STIFF TO STIFF, SLIGHTLY MOIST, MORE MOISTURE WITH DEPTH, BROWN.
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HAND DRIVEN LINER SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JULY 16, 2024.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPTH. THE SITE WAS RELATIVELY FLAT.
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 (PCT) (ISTU D 2216);
-200= PERGENTAGE PASSING No. 200 SIEVE (ASTM D 1140).
24-7-395 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
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SAMPLE OF: Sondy Silty Cloy
FROM:Plt3@5'
WC = 7.5 %, OO = 100 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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24-7-395 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5
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SAMPLE OF: Very Sondy Cloyey Silt
FROM:Pii4O4'
WG = 7.6 %, DD = 96 pcf
-2OO = 54 %
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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SWELL-CONSOLIDATION TEST RESULTS Fig. 424-7-395 Kumar & Associates