HomeMy WebLinkAboutSubsoils Study for Foundation DesignlGrtHäffirfiffifffirnriiå*"'
An Emdoycc Owncd 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, Foft Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
308 CINDYS \ilAY
GARFTELD COUNTY, COLORADO
PROJECT NO.22-7-738
FEBRUARY 17,2023
PREPARED FOR:
KATE FRATZKE
308 CINDYS WAY
RIFLE, COLORADO 81650
katefratzke@ gm ail. com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS.
FIEI,D EXPLORATION
SUBSURFACE CONDITIONS .......
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS
FOI]NDATIONS
FLOOR SLABS
TINDERDRAIN SYSTEM .....
SI]RFACE DRAINAGE.........
LIMITATIONS...
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2 - LOG OF EXPLORATORY BORING
FIGURE 3 - SV/ELL-CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Associates, lnc. o Project No.22-7-738
PURPOSE AND SCOPE OF STUDY
This report presents the results ofa subsoil study for aproposed residence to be located at
308 Cindys 'Way, north of Silt, 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 Kate Fratzke dated November I1,2022.
A field exploration program consisting of an exploratory boring was conducted to obtain
information on the general 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 analyzedto 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
The proposed residence will be a single-story structure about 950 square feet in plan size and
located as shown on Figure 1. Ground floor could be slab-on-grade or structural over
crawlspace. Grading for the structure is expected to be relatively minor with cut depths between
about 2 to 4 feet. V/e assume relatively light foundation loadings, typical of the proposed type of
construction.
If building loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The proposed building site was vacant grass pasture land at the time of our field exploration and
bordered by Cindys Way on the north and a driveway on the west. Topography at the site is
valley bottom with a gentle slope down to the south.
FIELD EXPLORATION
The field exploration for the project was conducted on December 28,2022. One exploratory
boring was drilled at the location shown on Figure 1 to evaluate the subsurface conditions.
The proposed building was located after the boring was drilled. The boring was advanced with
4-inch diameter continuous flight augers powered by a truck-mounted CME-458 drill rig and
logged by a representative of Kumar & Associates.
Kumar & Associates, lnc. @ Project No. 22'7-738
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Samples of the subsoils were taken with a 2-inch I.D. spoon sampler. The sampler was driven
into the subsoils at various depths with blows from a 140 pound hammer falling 30 inches. This
test is 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 Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory
for review by the project engineer and testing.
SUBSURFACE CONDITIONS
A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The
subsoils consist of about Yzfoot of topsoil overlying stiff to medium stiff, sandy to very sandy
silty clay underlain at a depth of about 8 feet by loose, silty sand to the boring depth of 21 feet.
Laboratory testing performed on samples obtained from the boring 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 silty clay, presented on Figure
3, indicate low to moderate compressibility under conditions of loading and wetting. The
laboratory testing is summarizedínTable 1.
Free water was encountered in the boring at a depth of about 9 feet at the time of drilling. The
upper soils were slightly moist becoming very moist and wet with depth.
FOUNDATION BEARING CONDITIONS
The upper clay soils possess low bearing capacity and low to moderate settlement potential. The
drier clay soils could possess a minor expansion potential. Spread footings placed on the natural
clay soils should be feasible for support of the proposed residence with a low risk of movement.
Presented below are recommendations for spread footings bearing on the natural soils. If
recommendations for spread footings bearing on compacted structural fill are desired to limit
movement risk, we should be contacted.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the natural silty clay soils with a low risk of settlement/heave, primarily if the bearing soils
were to become wetted.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
Kumar & Associates, lnc. @ Project No.22-7-738
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1) Footings placed on the undisturbed natural soils should be designed for an
allowable bearing pressure Based on experience, we expect initial1,500
2)
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less. There could be some additional post-construction
settlement or heave on the order of 1 inch, primarily if the bearing soils were to
become wetted.
The footings should have a minimum width of 18 inches for continuous walls and
2 feet" for isolated pads.
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. -"àContinuous foundation walls should be heavily 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 also be designed to resist a
laleral earth pressure conesponding to an equivalent fluid unit weight of at least
55 pcf for the onsite soils as backfill.
The topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to firm natural soils. The exposed soils in footing
areas should then be moistened and compacted.
A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
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4)
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FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade
construction with a risk of movement similar to shallow spread footings as described above. 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 relatively well
graded sand and gravel, such as road base, should be placed beneath floor slabs for support. This
material should consist of minus 2-inchaggregate with at least 50% retained on the No. 4 sieve
and less than 72o/o passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95%o of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
onsite soils or imported granular soils devoid of vegetation, topsoil and oversized rock.
6)
Kumar & Associates, lnc. o Project No.22-7-738
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LINDERDRAIN SYSTEM
It is our understanding the proposed finished floor elevation at the lowest level is at or above
the surrounding grade. Therefore, a foundation drain system is not required. It has been our
experience in the areathat local perched groundwater can develop during times of healy
precipitation or seasonal runoff. Frozen ground during spring runoffcan creale aperched
condition. We recommend below-grade construction, such as retaining walls and crawlspace
areas greater than 4 feet deep be protected from wetting and hydrostatic pressure buildup by an
underdrain and wall drain system.
If the finished floor elevation of the proposed structure is revised to have a floor level below the
surrounding grade, we should be contacted to provide recommendations for an underdrain
system. All earth retaining structures should be properly drained.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence 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 90o/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 12 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, such as sod, and sprinkler
heads should be located at least 5 feet from foundation walls. Consideration
should be given to use of xeriscape to reduce the potential for wetting of soils
below the building caused by inigation.
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
Kumar & Associates, lnc. @ Project No.22-7-738
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from the exploratory boring drilled at the location 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 extrapolation of the subsurface conditions
identified at the exploratory boring 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.
This report has been prepared for the exclusive use by our client for design pulposes. 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 recontmendations, and to verifli that the recoÍìmendations
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 & Associateso Inc.
Steven L. Pawlak, P.E
Reviewed by:
David A. Y
SLPlkac
P.E.
Cc: Jeff Johnson Architectural - Jeff Johnson (jeff@jiarchitectural.corg)
(t,15222
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22-7 -738 Kumar & Associates LOCATION OF EXPLORATORY BORING Fig. 1
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BORING 1 LEGEND
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TOPS0|L; SANDY SILTY CLAY WITH ORGANICS, FIRM, SLIGHTLY
MOIST, DARK BROWN.
|s/12
WC=8.1
DD= 1 07
cLAy (cL) sANDy T0 VERY SANDY, S|LTY, STTFF T0 MEDTUM
STIFF, SLIGHTLY MOIST TO VERY MOIST WITH DEPTH, BROWN.
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s/12
WC=19.0
DD= 1 04
-200=8 1
SAND (SM) S|LTY, SLTGHTLY CLAYEY, L00SE, WET, BRolVN
DRIVE SAMPLI, 2-INCH I.D. CALIFORNIA LINER SAMPLE
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,orrcDR|VE SAMPLE BL0W COUNT. INDICATES THAT 19 BL0WS 0F''I'. A 14o-PoUND HAMMER FALLING 30 INcHES wERE REQUIRED
TO DRIVE THE SAMPLER f2 INCHTS.
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DEPTH TO WATER LEVEL ENCOUNTERED AT THE TIME OF
= DRILLING,
---> DEPÏH AT WHICH BORING CAVED.
15 4/12
NOTES
THE EXPLORATORY BORING WAS DRILLED ON DECEMBER 28,
2022 V'IITH A 4-INCH DIAMETER CONTINUOUS FLIGHT POWER
AUGER.
20
2, THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED
APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE
SITE PLAN PROVIDED.
25
3. THE ELEVATION OF THE EXPLORATORY BORING WAS NOT
MEASURED AND THE LOG OF THE EXPLORATORY BORING IS
PLOTTED TO DEPTH.
4. THE TXPLORATORY BORING LOCATION SHOULD BE CONSIDERED
ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY
BORING LOG REPRESENT THE APPROXIMATI BOUNDARIES BETWEEN
MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATTR LEVEL SHOWN ON THE LOG WAS MEASURED AT
THE TIME AND UNDER CONDITIONS INDICATED. FLUCTUATIONS IN
THE WATER LEVEL MAY OCCUR WITH TIME.
7 LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSTTY (pcf) (lSrU O ZZr0);
-2OO = PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1 1 4o).
LOG OF EXPLORATORY BORING Fis. 222-7 -738 Kumar & Associates
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SAMPLE OF: Sondy Silty Cloy
FROM:Boringle^2,5'
WC = 8.1 %, DD = 107 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
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SWELL_CONSOLIDATION TEST RESULTS Fig. 322-7 -738 Kumar & Associates
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SOIL TYPE
81
1 at/
5
ATTERBERG LIMITS
Sandy Silty Clay
Sandy Silty Clay
GRADATION
t07
r04
8.1
19.0
SAMPLE LOCATION
DEPTHBORING LIQUID LIMIT
UNCONFINED
COMPRESSIVE
STRENGTH
PERCENT
PASSING NO.
2OO SIEVE
NATURAL
DRY
DENSITY
NATURAL
MOISTURE
CONTENT
SAND
("/ù
GRAVEL
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PLASTIC
INDEX
Pro No. 22-7-738