HomeMy WebLinkAboutSubsoil Study for Foundation Design 08.21.2023I(;rA[1fr1[ftrffi*'""r;"**5020 Cornty Road 154
Clcnwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
cmai l: kaglenwood@kumarusa.corn
An Employee Owned Gompony www.kunlarusa,com
OIfice Locations: Denver (HQ), Parker, Colorado Springs, Fon Collins, Ghnwood Sprirtgs, and $rmmit County. Clolondo
RECEIVED
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GAIRFIELD COI.JNTY
COMMUNITY DEVELOPMENT
SUBSOIL STUDY
F'OR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 8, FOUR ndILE RANCH
408 RED CLIFF'CIRCLE
GARFIBLD COUNTY, COLORADO
PROJECT NO.23-7-44s
AUGUST 21,2023
PREPARED FOR:
RICHARD DOOLEY
P.O. BOX 183
GLENWOOD SPRTNGS, COLORADO 81602
Richard. doolev@gmail.com
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TABLE OF'CONTENTS
PTIRPOSEAND SCOPE OF STTIDY..
PROPOSED CONSTRUCTION ....
SITE CONDITIONS
FIELD DGLORATION
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMEN DATION S
FOUNDATIONS .........
FOT]NDATION AND RETAINING WALLS ..
TT r\rrD ET AEIE1!VVA\ U!/ UU...r.
UNDERDRAIN SYSTEM
SURFACE DRAINAGE
LIMITATIONS....
FIGI]RE I - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF DGLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURES 4 and 5- SWELL-CONSOLIDATION TEST RESULTS
FIGTIRE 6 - GRADATION TEST RESULTS
.IABLE I- SUMMARY OF LABORA'I'ORY I'EST RESUL'I'S
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2
3
4
5
5
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Kumar & Assoclatee, lnc. 6 Prdect No. 23.7.4.1,5
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GAITFIhLD CT]UN"['Y
COMMUNITY DEVELOPMENT
PURPOSE ANI} SCOPE Otr'STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on
Lot 8, Four Mile Ranc[ 408 Red CliffCircle, Garfield County, Colorado. The project site is
shown 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 Richard Dooley dated July 24'2023.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the 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 analyzed to develop recommendations for foundation qryes, 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 assumed construction and the subsurface conditions
encountered.
PROPOSED CONSTRUCTION
The design for the proposed residence had not been determined at the time this report was
prepared but is assumed to be a one- and two-story wood frame structure located in the building
envelope shown on Figure l. Ground floors could be slab-on-grade or structuml above
crawlspace. Grading for the structure is assumed to be relatively minor with cut depths between
about 4 to l0 feet. We assume relatively light foundation loadings, typical of the proposed type
of construction.
If building loadings, location or grading plans differ significantly from those described above,
we should be notified to re-waluate the recommendations contained in this report.
SITE CONDITIONS
The site was vacant at the time of our field exploration. The lot slopes gently to moderately
down to the southwest, with little change in elevation across the building envelope. Vegetation
consists of sage brustr, grass and weeds.
FIELD EXPLORATION
The field exploration for the project was conducted on July 31,2023. Two exploratory borings
were drilled at the locations shown on Figure I to evaluate the subsurface conditions. The
borinp were 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 Kumar &
Associates, Inc.
Kumar & Assoclates, lnc.6 Project No.2Y74415
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Samples of the subsoils were taken with I % inch and 2-inch I.D. California type liner samplers.
The samplers were 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 bv
ASTM Method D-l586. 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 Logs of Exploratory Borings, Figure 2. The
samples were returned to otu'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 encountered, below about I foot of topsoil, consist of between about 6 to 7 feet of stiff
to very stiff, sandy clay and silt overlying relatively dense, siltrT sandy gravel with cobbles and
probable boulders down to the maximum drilled depth of 1l% feet. Drilling in the dense
grcnular soils with auger equipment was difficult due to thc cobblcs and probablc bouldcrs and
drilling refusal was encountered in the deposit in both borings.
Laboratory testing performed on samples obtained from the borings included natural moisture
content, dorsity, and gradation analyses. Results of swell-consolidation testing performed on
relatively undisturbed drive samples of the clay and silt soils, presented on Figures 4 and 5,
indicate low compressibility under light loading and a low to moderate hydrocompression
potential when wetted. The laboratory testing is summarized in Table l.
No free water was encountered in the borings at the time of drilling and the subsoils were moist.
FOUNDATION BEARING CONDITIONS
The upper clay and silt soils exhibit a low to moderate hydrocompression potential when wetted
that could result in post-construction building movement or distress. Care should be taken in the
surface and subsurface drainage arorurd the house to prevent clay bearing soils from becoming
wet. It will be critical to the long-term performance of the strucfure that the recommendations
for surface gading and subsurface drainage contained in this report be followed. The amount of
movement will mainly be related to the depth and extent of subsurface wetting of the clay and
silt soils. Extending the foundation bearing levels down to the ganular soils or replacing the
clay and silt soils with at least 2 feet of compacted structural fill could be provided to achievc a
lower risk of differential movement and distress.
DE SIGN RECOMMENDATI_ON S
FOTINDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
thc proposed construction, we recommend the building be founded with spread footings beartng
Kumar & Assoclates, lnc. @ Project No. 8.7.4415
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on the natural granular soils or on compacted structural fill bearing on the natural granular soils.
The hydrocompression potential of the clay and silt soils exposed at design bearing level should
be further evaluated for sub-excavation and replacement with compacted structural fill.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
l) Footings placed on the undisturbed soils or compacted structural fill should be designed
forana11owablebearingp'"*'ruLBasedonexperience,weexpectinitial
settlement of footings designed and consffuctEd as discussed in this section will be about
I inch or less with around % to I inch of post-construction settlement depending on the
bearing soil and wetting conditions.
2) The footings should have a minimum width of 16 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 above their bearing elevation for frost protection. Placement of foundations at
least 36 inches below exterior grade is typically used in this area.
4) Continuous foundation walls should be heavily reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least I 2 feet. Foundation
walls acting as retaining sffuctures should also be designed to resist lateral earth pressures
as discussed in the "Foundation and Retaining Walls" section of this report.
5) The topsoil, clay and silt soils, and any loose or disturbed soils should be removed and
the footing bearing level extended down to the firm natural soils. The exposed soils in
footing area should then be moistened and compacted. If needed, structural fill
consisting of 3/c-inch road base can be placed and compacted in thin lifts to at least 98%
of the maximum standald Proctor density at a moisfure content near optimum to re-
establish design footing bearing grades.
6) A representative of the geotechnical engineer should observe all footing excavations prior
to concrete placement to evaluate bearing conditions.
FOTINDATION AND RETAINING WALLS
Foundation walls and retaining structures which are laterally supported and can be expected to
undergo only a slight amount 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 bacldill consisting
of the on-site soils. Cantilevered retaining structures which are separate from the residence and
can be expected to deflect sufficiently to mobilize the full active earth pressure condition should
be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight
of at least 50 pcf for bacHill consisting of the on-site soils.
All foundation and retaining sffuctures should be designed for appropriate hydrostatic and
swcharge pressures such as adjacent footinp, haffic, consffuction materials and equipment. The
Kumar & Assoclates, lnc, o Project No. 2+744,5
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pressures recommonded above ttsfllmo d'rained conditions behind the wslls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure buildup behind walls.
Bacldill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at a moisture content near optimum. Bacldrll placed in pavement and
walkway arcas should bc compactcd to at least 95% of the maximum standard Proctor dcnsity.
Care should be taken not to overcompact the backfill or use large equipment near the wall, since
this could cause excessive lateral pressure on the wall, and increase expansion potential of clay
soils used as backfill. Some settlement of deep foundation wall backfill should be expected,
even if the material is placed correctly, and could result in disffess to facilities constnrcted on the
backfill. Backfill should not contain organics, debris or rock larger than about 6 inches.
The lateral resistance of fourdation or retaining wall footings will be a combination of the
sliding resistance of the footing on the foundation materials and passive earth pressure against
the side of the footing. Resistance to sliding at the bottoms of footings placed on the natrual
granular soils or on compacted structural fill can be calculated based on a coefficient of friction
of 0.45, and a coefficient of friction of 0.30 for footings placed on the clay soils. Passive
pressure of compacted bacldll against the sides of the footings can be calculated using an
equivalent fluid unit weight of 350 pcf. The coefficient of friction and passive pressure values
recommended above assume ultimate soil sffength. Suitable factors of safety should be included
in the design to limit the strain which will occur at the ultimate strengtlL particularly in the case
of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be
compacted to at least 95% of the maximum standard Proctor density at a moisture content near
optimum.
FLOOR SLABS
Lightly loaded slab-on-grade construction placed on the clay and silt soils will have a risk of
movement and distress. We recommend at least 2 feet of granular soil such as road base be
placed below slabs in clay and silt soil areas. To reduce the effects of some differential
movernent, floor slabs should be separated from all bearing walls and columns with expansion
joints which allow uuestrained 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 bensath basement level
slabs to facilitate drainage. This material should consist of minus 2-inch aggregate with at least
50% retained on the No. 4 sieve and less than?o/o passing the No. 200 sieve. All fill materials
for support of floor slabs should be compacted to at least 95% of maximum standard Proctor
Kumar & A,ssoclates, lnc. 6 Prdect No. 23.7.4r'l5
5
density at a moisture content near optimum. Required fill should consist of granular soils devoid
of vegetation, topsoil and oversized rock.
I-TNDERDRAJN SYSTEM
Although free water was not encountered during our exploratiorq it has been our experience in
the area and where there are clay soils that local perched groundwater can develop during times
of heavy precipitation or seasonal runoff. Frozen grourd during spring runoffcan create a
perched condition. We recommend below-grade consbrrction, such as retainingwalls,
crawlspace and basement areaso 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 I foot below lowest adjacent furish grade and sloped at a minimum lolo
to a suitable gfavity outlet or sump and pump. 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 bacldill should be at
least I % feet deep and covered with filter fabric such as Mirafi l40N or 160N.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
l) 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.
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
l2 inches in the first l0 feet in unpaved areas and a minimum slope of 3 inches in the
first l0 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 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
irrigation.
Kurnr & Assoclates, lnc.6 Prdect No. ?J.744r5
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LII\{ITATIONS
This study has been conducted in accordance with genu'ally accepted geotechnical engineering
principles ond prnctices in this area at this tirne. We makE no rvarrarrty either oxprest or implied.
The conclunions and recommendations srrhmitted in this repofi are hase<l npnn the data ohtained
from the exploratory borings drilled at the locotiorrs indicnted on Figurc l, the assumed typc of
construction and our experience in the area. Our services do not include determining the
presencc, preveirtion or possibility of mold or other biological contaminants (MOBC) developing
ilr the future. lf the client is concemed about MOBC, then a professional in this special field of
practice should be consulted. Our findings include interpolation and extrapolation of the
subsurface conditiotts identified at the exploratory borings and variations in the subsurface
conditions may not become evident until excavation is performed. if conditions encountered
during construction appear different trom those described in this report, we should be notified so
that re-evaluation of the recommendations mav be made.
This report has been prepared for the exclusive use by our clie,lrt for design puposes. We are not
responsible for technical interpretations by others of our information. As tlre project evolveso we
should provide {)ontinued consultation and field serices during construction to review and
monitor the implementation of our recornmendations, and to veriry that the reccmmendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recornmendations presented herein. We recommend on-site observation
of excavations and foundation bearing strata and testing of structural fiIl by a representative of
the geotechnical engineer.
Respectfllly Submitted,
Kumnr &
Robert L. Dutan,
Reviewed By:
DanielE. Hardin, P.E.
RLD/kac
Kumar & Associatcs, lnr, t Frojeo-l Ho, ?Xl-ddf'
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HOUSE T
APPROXIMATE SCALE_FIET
3tvWP
LOT 8
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23*7-445 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
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BORING 1
EL. 100'
BORING 2
El.101'
0 0
21 /12
WC='l 0.0
D0=92 17 /12
5 17 /12
WC=1 1.1
DD=88
-200=60
16/12
WC=8,6
DD=97
5
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IrFo-ul6 10
49/ 12 50/6
WC=4.1
+4=24
*2OO=28
10
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23-7-445 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fis. 2
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LEGEND
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TOPSOIL. SANDY CLAY AND SILT WITH ORGANICS, FIRM, SL]GHTLY MOIST' BROWN.
CLAY AND SILT (cL-ML)i SANDY, VERY STIFF, SLIGHTLY MolsT, BROWN, CALCAREOUS.
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GRAVEL (GM)r SANDY, SILTY, WITH COBBLES, DENSE, SLIGHTLY MOIST' TAN' SLIGHTLY
CALCAREOUS.
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DRIVE SAMPLE, 2.INCH I.D. CALIFORNIA LINER SAMPLE.
DRrVE SAMPLE, I 5/8-INCH l.D. SPLIT SPOON STANDARD PENETRATION TEST
^. I.^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 21 BLOWS OF A l4O.POUND HAMMER
''/ '' FALLTNG so tNcHEs wERE REQU|RED To DRtvE THE SAMPLER 12 lNcHEs.
I rnlcncll AUGER REFUsAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON JULY 31,2023 WITH A 4-INCH-DIAMETER
CONTINUOUS-FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PI.AN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER
TO BORING 1 AS 1OO, FEET ASSUMED.
4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE
ONLY TO THE DEGREE IMPLIED BY IHE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN TIIE BORINGS AT THE TIME OF DRILLING.
7. I-ABORATORY TEST RESULTS:
wc = WATER CONTENT (X) (lSrU OZZte);
DD = DRY DENSITY (pct) (ASTM D2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D69I3);
_2OO = PEREENTAGE PASSING NO. 2OO SIEVE (ASTM D11/TO).
23-7-445 Kumar & Associates LEGEND AND NOTES Fis. 3
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SAMPLE OF: Sondy Sllt ond Cloy
FROMrBoririglA2'
WC - 10.0 ft, DD - 02 pcf
ADDITIONAT COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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6b M. rir hdr! rwfHdbAdd,6!tln
h/L dUEt h fr oFdnl dk od lmHr hc. SrI6mlffi d4Fbdlh&ffAflO-.&
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t.0 APPUED PRESSURE - KSF IO
23-7-445 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fis. 4
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SAMPLE OF: Sondy Sllt ond Cloy
FROM:Boring2Ol'
WC = 8.6 X, DD = 99.7 pcf
NO MOVEMENT UPON
WETTING
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23-7-445 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5
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'pFnpadu .q pc ilDqr l,odu tu|tDl,ql 'p.lrl ur qclqr rlduB.ql ot lt$ ltddo qtm tst...ql
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TABTE I
SUMMARY OF I.ABORATORY TEST RESULTS
Ulr'SGRAI'AIITil
LNUID UITI
041
PLAS'IC
I{DEX
l{}Ian
tr{coNHilE)
corPRESSlvE
STREIIGTH g(tLTYPEBfiII{G
Iil
DEPTH
tqal
NATURA
TOFTURE
co{rEilr
I{ATURAL
DRY
DBISITY
1ili
GRAVEL
(16)
SA'{D
(jt)
PERCENT
PASSINGNO.
200 sra/E
Sandy Silt and ClayI210.0 92
Sandy Silt and Clay6041l.l 88
Sandy Silt and Clay97248.6
28 Gravelly Silty Sand94.1 24 48