HomeMy WebLinkAboutSubsoil Study for Foundation Design 07.12.2022I (¡rt $,iffi;fi*trËsn'"'Ê;n'*^
An Employcc O{rncd 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 Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
July 12,2022
Terry Gambrel
P.O. Box 188
New Castle, Colorado 81647
teaelexinc@live.com
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Project No.22-7-347
Subject:Subsoil Study for Foundation Design, Proposed Shop Building,4050 County
Road 3l l, Divide Creek Road, Garfield County, Colorado
Dear Terry:
As requested, Kumar & Associates, Inc. observed the pits which were dug for design of
foundations at the subject site. The study was conducted in accordance with our agreement for
geotechnical engineering services to you dated May 6,2022. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: The proposed shop will be approximately 30 feet wide by 50 feet long
located on the site as shown on Figure 1. Ground floor will be slab-on-grade. Cut depths are
expected to be relatively minor. Foundation loadings for this type of construction are assumed to
be relatively light to moderate and typical of the proposed type of construction. We understand
that a thickened edge slab is the preferred foundation system.
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 is relatively flat. There is no vegetation in the
proposed building area and there appears to be up to one foot of existing fill. There is some sage
brush and trees around the building area. There is a steep slope down to the west below County
Road 3 1 I , to the east of the proposed building area. Divide Creek is located across the driveway
to the west of the proposed building area.
Subsurface Conditions: The subsurface conditions at the site were evaluated by observing
three exploratory pits previously excavated at the approximate locations shown on Figure l. The
logs of the pits are presented on Figure 2. The subsoils encountered, below about up to I foot of
road base and clay fill, consist of l%to ZYz feet of clay overlying relatively dense, slightly silty,
sandy gravel with cobbles. Results of swell-consolidation testing performed on a relatively
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undisturbed sample of sandy silty clay, presented on Figure 3, indicate low compressibility under
existing moisture conditions and light loading and a minor settlement potential when wetted.
Results of a gradation analysis performed on a sample of the slightly silty sandy gravel with
cobbles (minus 5-inch fraction) obtained from the site are presented on Figure 4. Free water was
only observed in Pit 3 at a depth of 4 feet and the upper soils were moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings or a
thickened edge slab placed on the undisturbed natural soil designed for an allowable soil bearing
pressure of psf for support of the proposed shop. The clay soils tend to compress after
wetting and there could be some post-construction foundation settlement. Footings or the
thickened edge of the slab should be a minimum width of 16 inches for continuous walls and
2 feet for columns. Loose and disturbed soils and existing fill 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 or insulation should be placed for frost protection. Placement of
footings at least 36 inches below the exterior grade is typically used in this area. Continuous
foundation walls (if any be reinforced top and bottom to span local anomalies such as by
assuming an unsupported length of at least l0 feet. Foundation walls acting as retaining
structures (if any) 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, are suitable to support lightly to
moderately 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 to facilitate
drainage. This material should consist of minus 2 inch aggregate with less than 50%o passing the
No. 4 sieve and less than 2o/opassingthe 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 fill can consist of road
base or screened rock devoid ofvegetation, topsoil and oversized rock.
Kumar & Associates, lnc. o Projec{ No. 22-7-347
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Underdrain System: A underdrain should not be needed for the proposed slab-on-grade
construction
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the shop has been completed:
1) Inundation ofthe 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 the maximum standard Proctor density in pavement and slab areas
and to at least 90%o 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 l0 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 atthis 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 I
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
Kumar & Associates, lnc. o Project No. 22-7-347
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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.
Ifyou have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
Kumar & Associates,
Daniel E. Hardin, P.
Reviewed by:
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Steven L. Pawlak, P.E.
DEH/kac
attachments Figure 1 - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Swell-Consolidation Test Results
Figure 4 - Gradation Test Results
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Kumar & Associates, lnc. @ Project No. 22-7-347
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APPROXIMATE SCALE-FEEÏ
22-7 -347 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
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WC= 19.2
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LEGEND
FILL: ROAD BASE SANDY GRAVEL WITH SCREENED ROCK, SCATTERED COBBLES, MEDIUM
DENSE, MOIST, BROWN (tN P|TS 't AND 2). THE F|LL CONSTSTED OF MOSTLY CLAY W|TH
ROOTS AND EALING TWINE IN PIT 3.
CLAY (Ct); SILTY, SANDY, MEDIUM STIFF, MOIST, BROWN.
GRAVEL (GM-cP); SANDY WITH COBBLES, SLIGHTLY SILTY, DENSE, MOIST TO wET, BROWN
HAND DRIVE SAMPLE
DISTURBED BULK SAMPLE
---> DEPTH AT WHICH PIT HAD CAVED.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE PRIOR TO OUR SITE VISIT ON MAY
6, 2022.
2. THE LOCATIONS OF THE EXPLORAÏORY PITS WERE MEASURED APPROXIMAÏELY BY PACING FROM
BUILDING CORNERS STAKED IN THE FIELD.
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 ÏHE 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 LEVELS SHOWN ON THE LOGS WERE MEASURED AT THE TIME AND UNDER
CONDITIONS INDICATED. FLUCTUATIONS IN THE WAÏER LEVEL MAY OCCUR WITH TIME.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (PCI) (ASTU D 2216);
+4 = PERCENTAGE RETAINED oN No. 4 SIEVE (ASTM D 422);
_2OA= PERCENTAGE PASSING NO.2OO SIEVE (ASTM D 1140).
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LOGS OF EXPLORATORY PITS Fig. 222-7 -347 Kumar & Associates
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SAMPLE OF: Sondy Silty Cloy
FROM: Pit 1 @ 1'
WC = 14.2 %, DD = 104 pcf
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ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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22-7-347 Kumar & Associates SWELL-CONSOLIDATION TEST RESULT Fig. 3
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HYDROMETER ANALYSIS SIËVE ANALYSIS
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U.S. SANOARD SERIES
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CUAR SOUARE OFENITOS
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.oor .oo2 .oo5 .ot 9 .125 2.OOF PARTICLES IN MILLIMETERS
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CLAY TO SILT COBBLES
GRAVEL 28 % SAND 66 %
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Sl¡ghtly Silty Sondy Grovel wilh Cobbles
SILT ANO CLAY 6 ?6
FROM:Pit1O2.5'-3'
lh.ec lssl rosulls opÞly only lo lho
rompl.s whlch e.r. lasLd. Thc
l63llng.oport sholl nol br raproducrd,
e¡cspl ln full, wllhoul lhe vrltlen
qpprovql ol Kumqr & Asgoclot.s, lnc,
Slavo qnoly3ls l.ílng l¡ Þcrfomed ln
ocêordoncc wlth ASTM 06913, ASTM 07928,
ASTM C136 qnd/or ASTI¡ Dll40.
SAND GRAVEL
FINE MEDTUM lCOrnSe FINE COARSE
22-7-347 Kumar & Associates GRADATION TEST RTSULTS Fig. 4