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SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDE¡{CE
3554 COUNTY ROAD 2I4
SILT. COLORADO
PROJECT NO.22-7-406
JULY 7,2022
PREPARED FOR:
DAYBREAK CONSTRUCTION
ATTN: DANA YERIAN
P.O. BOX 587
GLEÀIWOOD SPRINGS, COLORADO 81602
davbreakconst@hotmail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY.
PROPOSED CONSTRUCTION ........
SITE CONDITIONS...
FIELD EXPLORATION .....
SUBSURFACE CONDITIONS
FOT}NDATION BEARTNG CONDTTIONS
DESIGN RECOMMENDATIONS ...............
FOUNDATIONS
FOUNDATION AND RETAINING WALLS
FLOOR SLABS
UNDERDRAIN SYSTEM .....
SURFACE DRAINAGE........,
LIMITATIONS
FIGURE, I - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGIJRE,3 - LEGEND AND NOTES
FIGURES 4 and 5 - SWELL-CONSOLIDATION TEST RESULTS
TABLE I- SUMMARY OF LABORATORY TEST RESULTS
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PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located at
3554 County Road 214, Silt, Coloraclo. The project site is sholi'n on Figure l. 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 Daybreak
Construction dated ïu:ne 1,2022.
A field extrrloration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Sarnples of the subsoils obtained during the field
exploration rvere testecl in the laboratory to determine their classifìcation, compressibility or
swell and other engineering characteristics. The results of the 1ìelcl exploration and laboratory
testing were analyzed to develop recornmendations for foundation types, depths and allowable
pressures for the proposed building fcrundation. This report summarizes the data obtairred during
tliis study and presents oul conclusions, design recomrnendations and other geotechnical
engineering consiclerations based on the proposed constmction and the subsurface conclitions
encountered.
PROPOSED CONSTRUCTION
The proposecl residence will be a one-story wood-frame structure over a partial basement with
attached garage. Ground floors will be a combination of slab-on-grade and strucfural over
crawlspace. Grading for the structure is assumed to be relatively miuor with cut depths between
about 3 to l0 feet. We assume relatively light foundation loadings, typical of the proposed type
of construction.
tf building loadings, location or grading plans change significantly from those described above,
we shoulil be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The subject site was developed with a single-story residence over a lower basement level (which
will be rernoved). The grourd surfäce is relatively flat with a gentle slope down to the south.
An inigation ditch was tlowing along the west property line. Vegetation consists of landscaped
lawn. bushes and deciduous trees.
FIELD EXPLORATION
The field exploration for the project was conducted on June 13, 2A22. Two exploratory borings
were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The
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borings lvere advanced with 4-inch diameter continuous flight augers powered by a truck-
mounted CME-458 drill rig. The borings were logged by a representative of Kunar &
Associates, Inc.
Samples of the subsoils were taken rvith a 2-inch I.D. spoon sampler. The sarnpler was cldven
into the subsoils at rrarious depths with blows from a 140-pound harntner falling 30 inches. This
test is similar to the standard penettation 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
slrown on the Logs of Exploratory Borings, Figure 2. The sarnples were returned to our
laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils encountereci below about %lootof topsoil consist of loose to vety loose, clayey to very
clayey sand down to the maxirnum explored clepth of 40 feet. A layer of medium stiff, sancly
clay was encountered in Boring I below the topsoil fromYz to 4 feet deep.
Laboratory testing perftrrmecl on samples obtained fiom the borings inoluded natural moisture
content and density and finer than sand grain gradation analyses. Results of swell-consolidation
testing performed on relatively undisturbed drive samples of the very clayey sand, presented on
Figure 4. indicate low to moderate compressibility under conditions of loacling and wetting. The
laboratory testing is summarized in Table 1.
No fì'ee lvater was encountered in the borings at the time of drilling and the subsoils were moist
to very moist.
FOUNDATION BEARING COI\DITTONS
The clayey sand soils encountered in the borings possess low bearing capacity and low to
moderate settlement potential. Boring I was drilled to a maximum depth of 40 feet and no dense
granular soils or hard bedroc,k rnaterial was encountered. Lightly loaded spread t-ootings plaoed
on the clayey sand can be used for support of the proposed residence with a risk of settlement.
Provicling a clepfh of sfnrcfilral fi11, lypically 3 feet, helow the spread fbotings can reduce the risk
of settleruent. Provided belorv are recomlnendations for a spread footing foundation system
bearing on the natural soils. If recommendations for strucfi.ral fill are desired, we should be
contacted to provide thern.
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DESIGN RECOMMENDATIONS
FOLINDATIONS
Considerìng the subsurface conditions encountered in the exploratory borings and the nature of
the llroposed construction, we recommend the building be founded with spread footings bearing
on the natural soils.
The design and constnrction criteria presented below should be observed tbr a spread footing
foundation systern.
1) Footings placecl on the undisturbed natural soils shoulct be clesigned for an
allowable bearing pressure of 1,500 psf. Based on experience, we expect
seftlernent of footings designed and constructed as discussed in this section will
be about lY" inch or less.
2) The footìrrgs should have a minimum width of 20 inches for continuous walls and
2 feet for isolated pads.
3) Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover al¡ove their bearing elevation for û'ost pt'otection. Placement
of foundations at least 36 inches below exterior grade is typically used in this
area.
4) Continuous foundation wal1s should be heavily reinforced top and bottotn to span
local anomalies and better r¡'ithstand differential movement such as by assurning
an uûsupported length of at least l4 feet. Formdatiou rvalls acting as retaining
structures should also be designed to resist lateral earth pressures as discussed in
the "Foundation and Retaining Walls" section of this report.
5) All existing fill, topsoil and any loose disturbed soils should be rentoved and the
footing bearing level extended down to the relatively firm natural soils, The
exposecl soils in footing areas should then be moistened and compacted. If water
seepage is encountered, the footing areas should be dewatered lrefore concrete
placement.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOUNDATION AND RETAINiNG WALLS
Foundation r.valls ancl retaining stmctures which are laterally supported and can be expected to
undergo only a slight arnount of deflection should be designed for a lateral earth pressure
computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting
of the on-site soils. Cantilevered retaining süructures which are separate frorn the residence ancl
can be expectecl to cleflect sufficiently to ruobilize the full active ea$h pressure condition should
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be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight
of at least 45 pcf for backfill consisting of the on-site soils.
All f'ounclation arrd retaining structures should be designed for appropriate hyclrostatic artd
surclrarge pressures such as adjacent footings, traffic, construction materials and equipment. The
pressures recommended above assune drained conditions behind the walls and a horizontal
backfill surface. The builclrrp of water behind a wall or an upward sloping backfill surface will
increase the lateral pressure imposed on a foundation wall or retaining stntcture. An underdrain
should be prorìded to prevent hydrostatic pressure buildup behind walls.
Backfill should be placed in uniform lifts and compacted to at least 90o/o of the maximum
standard Proctor density at a moisture content near optimum. Backfìll placed in pavement attd
walkway areas should be compacted to at least 95o/o of the maximum standard Proctor density.
Care should be taken not to overcornpact the backfill or use large equipment near the wall, since
this could calrse excessive lateral pressure on the wall, Some settlement of deep foundation wall
backfill should be expected, even if the traterial is placecl correctly, and could result in clistress to
t'acilities constructed on the backfitl.
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resistance of the footing on tlie foundation materials and passive earth pressure against
the side of the footing. Resistance to sliding at the boltoms of the footings can be calculatecl
based on a coefficient of friction of 0.35. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluici unit weight of 375 pcf. The
coefflcient of friction and passive pressure values reconrmended above asswï.e ultimate soil
strength. Suitable factors of safety should be included in the design to limit the strain which will
occur at the ultinate strenglh, particularly in the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads shoulci be cotnpacted to at least 95% of the
maxirnum standard Prcctor density at a moistwe content near optirnurn.
FLOOR SLABS
The natrral on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-gratle
construction. To reduce the effects of some differential movement, floo¡ slabs should be
separated from all bearirg walls and colurnns with expansion joints which allow unrestrained
veftical rnovement. Floor slab control joints should be used to reduce damage due to shrinkage
cracking. The requirenents for joint spacing and slab reinforcement should be established by the
ciesigner based on experience and the intended slab use. A minimmn 4-inch layer of relatively
well graded sancl and gravel should be placed beneath basement level slabs ttrr support. This
material should consist of minus 2-inch aggregate r.vith at least 50% retained on the No. 4 sieve
and less thatl2o/o passing the No.200 sieve.
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All fill materials for support of f'loor slabs should be compacted to at least95Yo of maximunr
standard Proctor clensity at a moisture content near optimum. Required fill can consist of the
on-site granular soils devoid of vegetation, topsoil and oversized rock^
UNDERDRAIN SYSTEM
Although fì'ee water was not encountered during our exploration, it has been our experience in
the area that local perched groundrvater can develop during times of heavy precipitation or
seasonal runoff. Frozen ground during spring runoff can create a perched condition. 'We
recomrnend 6.1eq,-grade construction, such as retaining walls, crawlspace and basement ateas,
be protected from wetting and hydrostatic pressure buildup by an underdrain system.
The drains should consist of clrainpipe placed in the bottom of the wall backfill surrourded above
the invert level vi'ith free-draining granular material. The drain should be placed at each level of
excavation and at least 1 foot below lowest adjacent tìnish gracle and sloped at a minimum lYo to
a suitable gravity outlet or sump and purnp. Free-draining granular material usecl in the
underdrain system should contain less than 2o/opassing the Nr¡. 200 sieve, less than 50% passing
tlre No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at
least I Yzfeet deep arrd covered with filter fabric such as Mirafi 140N or 160N.
SURFACE DRAINAGE
The follor.ving drainage precautions should be observed cluring construction ancl maintained at all
times after the residence has been completed:
1) Inrndation of the founclation excavations and underslab areas should be avoided
during constnrction.
2) Exterior backfill should be adjustecl to near optimum moisture and compacted to
at least 95Yo of the maxirnun standard Proctor density in pavement and slab areas
and to at least 90o/o o{ the rnaximum standard Proctor density irr larrdscape areas.
3) The ground surface surrounding the exferior of tire building should be sloped to
clrairr away from the foundation in all directions. We recommend a minimum
slope of 6 inches in tlre first 10 fbet ìn unpaved areas and a minimum slope of
3 inches in the first 10 feet in paved areas. Free-chaining rvall 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.
4) Roof downspouts and drains should discharge well beyond the limits of ail
backfill.
5) Landscaping which requires regular hear.y irrigation shoulcl be located at least
5 feef from foundation walls.
K¡mr & *sosciates, lnc. o Froj'cnt lt{e., Ær-,T406
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LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this areaatthis 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 borings drilled at the locations 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 interpolation and extrapolation of the
subsurface conditions idèntified at the exploratory borings and variations in the subsurface
conditions may not become evident until excavation is performed. If conditions encountered
during conskuction 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 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 veri$ 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.
Respectfully Submitted,
Ku¡nar & Associ:rte;, lnt
James H. Parsons, P
Reviewed by:
Daniel E. Hardin, P.E.
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22-7 -446 Kumar & Associates LOCATION OF TXPLORATORY BORINGS Fig. 1
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BORING 2
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LEGEND
TOPSOIL. CLAY, SANDY, ORGANIC, FIRM, MOISÏ, DARK BROWN.
CLAY (CL); SÀNDY, MEDIUM STIFF, MOIST, BROWN.
SAND (SC); CLAYEY IO VERY CLAYEY, SILTY, LOOSE TO VERY LOOSE, VERY MOIST,
BROWN.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
ezr,¡ DRTVE SAMPLE BLOW COUNT. IND|CATES THAT 6 BLOWS OF A 14o-POUND HAMMER"/ . . FELLING 50 INCHES WERE REQUIRED TO DRIVE THE SAMPLER .I2 INCHES.
.-> BEPTH AT WHICH BORING CAVED.
NOTES
1 THE EXPLORATORY BORINGS WERE DRILLED ON JUNE 13, 2422 WITH A 4-INCH_D¡AMETER
CONTINUOUS-FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE S E PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXFLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER
TO THE EXISTING FINISHED FLOOR EL. 1OO" ASSUMED.
4. TIIE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE
ONLY TO THE DEGREE IMPLIED BY THE MEÏHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENÏ THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AÏ THE TIME OF DRILLING
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2?16);
DD = DRY DENSIIY (pcf) (ASTM D2216);
-ZQO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D1140).
Fig. 3LEGEND AND NOTES22-7 -406 Kumar & Associates
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SAMPLE OF: Cloyey Sond
FROM:Boringl@5'
WC = 20.6 %, Ðù = 142 pcl
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ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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22-7-446 Kumar & Associates SWELL_CONSOLIDATION TTST RESULT Fis. 4
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SAMPLE OF: Cloyey Sond
FROM: Boring 1 @ 10'
DD = 111 pcf
ÁÐDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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SWTLL_CONSOLIDATION TIST RTSULT Fig. 522-7 -406 Kumar & Associates
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No. 22-7-406
Clayey Sand
Clayey Sand
Clayey Sand
Clayey Sand
Clayey Sand
43
102
111
il0
108
106
20.6
16.0
t7.8
19.2
5
10
0I
15
20
2
1
SOIL TYPEUQUID LIMITDEPÏHBORING
GRADATION UNCONFINED
COMPRESSIVE
STRENGTH
PLASTIC
INDEX
PERCENT
PASSING NO.
200 stEVE
NATURAL
DRY
DENSITY
NAÏURAL
MOISTURE
CONTENT
SAND
%t
GRAVET
(%)