HomeMy WebLinkAboutSubsoil Study for Foundation Design 10.19.2021ICrti,'iffif;ffiËsni'iiå*"'
An Employcc ûrncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwoodf@kurnarusa.com
www.kumarusa.com
Ollìcc Locations: Dcnver (HQ), Parke¡ Colorado Springs. Fort Collins, Glenrvood Springs, and Summit C,ounty, Color¿do
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
2808 COUNTY ROAD IIl
GARFTELD COUNTY, COLORADO
PROJECT NO. 18-7-692
ocToBER 19,2021
PREPARED FOR:
DM NEUMAN CONSTRUCTION
ATTN: JASON NEUMAN
P.O. BOX 2317
GLENWOOD SPRTNGS, COLORADO 81601
imn@dmneuman.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION ....
SITE CONDITIONS
FIELD EXPLORATION
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS
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
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - GRADATION TEST RESULTS
TABLE I- SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Associates, lnc. o Project No. 18-7-692
PURPOSE AND SCOPE OF STUDY
This report presents the results ofa subsoil study for a proposed residence to be located at
2808 County Road 117 (4-Mile Road), Garfield County, Colorado. The project site is shown on
Figure 1, The pulpose of the shrdy was to develop recommendations for the foundation design.
The shrdy was conducted as additional seruices to and in accordance with our agreement for
geotechnical engineering services to DM Neurnan Construction dated November 13, 2018.
A fîeld exploration program consisting of exploratory borings was conducted to obtain
infonnation on the subsurface conditions. Samples of the subsoils obtained during the field
exploration were tested in the laboratory to determine their classification and other engineering
characteristics. The results of the field exploration and laboratory testing were analyzed to
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, clesign recommendations and other geotechnical engineering considerations basecl
on the proposed constructiolr and the sulrsurface conditions encountered.
PROPOSED CONSTRUCTION
Design plans for the residence were in progress at the time of our stucly. The proposed residence
will be a woocl-frame structure locatecl as shown on Figure 1. Ground floor will be structural
over crawlspace in the residence and slab-on-grade in the garage. Grading for the structure with
respect to the existing site grade is proposed to be relatively minor. 'We 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 CONDITIOI{S
The ground surface in the building area is relatively flat with a gentle slope down to the nofih
and a few feet of estimatecl elevation difference. The site is a small valley bottom r.vith a steep
hillside to the east and moderate slope to the west. The building site was disturbed and fillecl by
past grading including backfilling of an effluent sewage treatment pond. Vegetation consists of
weeds with native brush and trees on the adjacent natural slopes.
Kumar & Associates, lnc. Ô Project No. 18-7-692
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FIELD EXPLORATION
The field exploration for the project was conducted on September 1, 2021. Three exploratory
borirrgs were drilled at the locations showr on Figure 1 to evaluate the subsurface conditions.
The borings were advanced with 4-inch diameter continuous tlight augers powered by a truck-
mounted CME-458 drill rig. The borings were logged by a representative of Kumar &
Associates.
Samples of the subsoils were taken with l% irrch and 2-inch I.D. spoon samplers. The samplers
were driven into the subsoils at various depths with blows f,'om a 140 pound hammer falling 30
inches. This test is similar to the standard penetration test described by 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. 'lhe samples 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 Figwe 2. The
subsoils encounTered consist of about I to 13% feet of loose, silty clayey sand with gravel to
sandy silty clay flrll overlying medium stiff to stiff silty sandy clay in Borings I and 3 and
organic clay in Boring 2 underlain at depths of I0% to 18 feet by relatively dense, silty sandy
gravel, cobbles and boulders to the drilled depths af l3Yz to 26 feet. Drilling in the coarse
granular subsoils with auger equipment was difficult cltre to the cobbles and boulders and drilling
refusal was encountered in tlie deposit. The organic layer encountered at Boring 2 below the fill
soils is interpreted as pond bottom muck and could be present below much of the proposed
building site.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density, gradation analyses and liquid and plastic limits. Results of gradation
analyses performed on small diameter drive samples (tninus l%-inch fraction) of the coarse
granular subsoils are shown on Figure 4. The laboratory testing is sunmarized in Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to very moist.
Kumar & Associates, lnc. ô Project No. 18-7-692
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FOUNDATION BEARING CONDITIONS
The fill material encountered in the borings appearu to be relatively loose and not placed for
structural support of building or driveway/parking loads. The fill soils appear relatively clean
and should be suitable for use as structural till after complete removal down to the native soils.
Organic soils such as encountered in Boring 2 should be discarded. Stmctural fill placed up to
footing bearing level throughout the entire building fooþrint and below driveway and parking
areas should be compacted to at least 987o of standard Proctor density at near optimurn moisture
content. The structural fill should extend laterally beyond the building foundation or pavement
edge a distance of at least one-half the fill depth below the foundation or pavement section. The
suitabitity of the existing fîll as structural material should be further evaluated at the time of
construction.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borirrgs arrd the nature of
the proposecl construction, we recommend the builcling be founded with spread fbotings bearing
on properly placed and compacted structural fill with a risk of long-term settlement depending on
the depth and quality of the structural fill. If extending the bearing down to the underlying
dense, natural coarse granular soils is desired for low settlement dsk, we should be contacted for
additional analysis and recotnmendations.
The design and constnrction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on compacted structural fill should be designed for an allowable
bearing plessuïe of 2,000 psf. Based on experience, we expect initial settlement
of footings designed and constnrcted as discussed in this section will be about 1
inch or less. Additional long-term settlement could be around l% of the fill depth
or about I to 2 inches for possible fill depths of l0 to 15 feet.
2) The footings should have a minimum width of 18 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 fi'ost protection. Placement
of foundations at least 36 inches below exterior gracle is typically used in this
ãTea.
Kumar & Associates, lnc. o Projec't No. 18:l-692
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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 14 feet.
Foundation walls 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.
All existing fill, organics and any loose or disturbed soils should be removed
down to the undisturbed natural soils. The exposed soils should then be moisture
adjusted to near optimum and compacted. lf soft soils are encountered. the
surbgrade should be stabilized before fill placernent.
A representative of the geotechnical engineer should evaluate structural fill
compaction on a regular basis duing placement and observe all footing
excavations prior to concrete placement for bearing conditions.
FOLTNDATION AND RETATNING WALLS
Foundation walls and retaining structures which arcTaterally supported and can be expected to
undergo only a slight amount of cleflection should be designed for a lateral earth pt'essure
oomputed on the basis of an equivalent fluid unit weight of at least 50 pcf for baokfill corrsisting
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 eafih pressure computed on the basis of an equivalent fluid unit weight
of at least 40 pcf for backfill consisting of the on-site soils. Backfill should not contain organics,
debris or rock larger than about 6 inches.
Atl foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The
pressures recommencled above assume drained conditions behind the walls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
increase the lateral pressure irnposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure builclup behind walls.
Backfill should be placed in unifonn lifts and compacted to at least 9AYo of the maxrmum
standarcl Proctor density at near optimum moisture content. Backfill placed in pavement and
walkway areas should be compacted to at least95o/o of the maximum standard Proctor density.
Care should be taken not to overcompact the backfill or use large equiptnent near the wall, since
this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall
backfîll should be expected" even if the material is placed conectly, and could result in distress to
facilities constructed on the backfill.
5)
6)
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The lateral resistance of foundation or retaiuing 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 bottorns of the footings can be calculated
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 fluid unit weight of 350 pcf. The
coefficient of friction and passive pressure values recotnmended above assurne ultimate soil
strength. Suitable factors of safety should be included in the design to limit the strain which will
occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against
tlre sides of the footings to resist lateral loads should be compacted to at least 95o/o of the
maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
Structural fill soils placed as pafi of the building site development are suitable to support lightly
loaded slab-on-gracle construction with a settlement risk similar to footings. To reduce the
effects of some differential rnovement. floor slabs should be separated ÍÌom all bearing walls and
columns with expansion joints which allow unrestrainecl vertical tnovement. Floor slab control
joints shoulcl 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 interior slabs for subgrade. This material should consist of
minus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less than l2o/o passing
the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least95o/o of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site soils devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
mountainous areas that local perched groundwater can der.elop during times of heavy
precipitation or seasonal runofT. Frozen ground during spring runotT can create a perched
condition. We recommend below-grade construction, such as retaining walls, crawlspace and
basement areas, be protected frorn wetting and hydrostatic pressure buildup by an underdrain
system.
The drains should consist of drainpipe placed in the bottom of the wall backfill sunounded above
the invert level with free-draining granular material. The drain should be placed at each level of
Kumar & Associates, Inc. o Project No. 18-7-692
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excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum Io/o to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2Yo passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a
nraximum size of 2 inches. The drain gravel baclcfill should be at least llz feet deep. An
impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a trough
shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils.
SURFACE DRAINAGE
Providing proper surface grading and drainage will be important to keeping the bearing soils dry
and limiting settlement of the building and site itnprovements. The following drainage
precautions should be observ'ed during construction and maintained at all times after the
residence has been completed:
1) Inundation of the foundation excavations and underslab areas should be avoided
cluring construction.
2) Exterior backfill should be adjusted to near optirnum moisture and compacted to
at least 95Yo of the rnaximurn standard Proctor density in pavernent and slab areas
and to at least 90Yo of the maximum standard Proctor density in landscape ateas.
3) The ground surfãce sunouncling the exterior of the building should be sloped to
drain away from the foundation in all directions. We reconrmend a minimum
slope of 12 inches in the first l0 feet in unpavecl areas and a minirnum 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 ou-site soils to
reduce surface water infiltration.
4) Roof downspouts and drains should discharge wellbeyond the lirnits of all
backfill.
5) Landscaping which requires regular heavy inigation should be located at least
5 feet fi'orn fourdation walls. Consideration should be given to use of xeriscape
to recluce the ¡rotential tbr 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 atthis time. 'We make no warranty either express or irnplied.
The conclu"qions 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 out experience in the area. Our services do not include determining the
presence. prevention or possibility of mold ol other biological contaminants (MOBC) developing
Kumar & Associates, lnc. @ Project No, 18-7S92
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in the future. If 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 conditions 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 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 continue.d consultation and field services during construction to review and
monitor the implementation of our recommendationso and to veriff 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,
Kumar & Associates, Inc.
Steven L.
Reviewed by:
Þ,,.^..ß
Daniel E. Hardin, P.E.
SLP/kac
cr: DM Neuman Construction - Rich Carter (rich@drnLreuman.com)
Kumar & Associates, lnc.iì Project No, 18-7-692
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18-7 -692 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
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BORING ,I BORING 2 BORING 5
0 0
12/12 5/ 12 s/12
5 1s/ 12 7 /12
e/ 12
WC= 17.8
DD= 1 06
-2QQ=79
9/6,16/6
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DD=1'l 5
47 /12
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7 /12
10 4/12 10
21 /12
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+4=30
-2OO=17
20 20
62/ 12
WC=4.6
+4=57
-200= 1 5
25 50/o
5o 3o
26/12
WC=15.1
-2OQ=49
LL=21
Pl=2
18-7 -692 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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LEGEND
FILLI CLAYEY SILTY SAND TO SANDY SILTY CLAY, SCATTERED GRAVEL TO GRAVELLY, LOOSE,
SLIGHTLY MOIST TO MOIST, RED-BROWN.
CLAY (CL); SILTY, SANDY TO VERY SANDY, MEDIUM STIFF To STIFF, MolST, BROWN
ORGANIc CLAY (CL); SILTY, SANDY, SOFT, VERY MOIST, GRAY-BROWN
GRAVEL, COBBLES & BOULDERS (CV); SII-IY, SANDY, DENSE, SLIGHTLY MOIST, MIXED BROWN,
BASALT AND SANDSTONE ROCK.
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DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
DRTVE SAMPLE, 1 3/8-|NCH t.D. SPLrr SPOON STANDARD PENETRATION TEST
-;,^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 7 BLOWS OF A 14O-POUND HAMMER'/ '' FALLTNG 30 TNCHES wERE REQUTRED To DRIvE THE sAMpLER '12 tNcHES.
I PRACTICAL AUGER REFUSAL.
NOTES
1 . THE EXPLORATORY BORINGS WERE DRILLED ON SEPTEMBER 1, 2021 WITH A 4-INCH DIAMETER
CONTINUOUS-FLIGHT POWER AUGER.
2, THE EXPLORATORY BORINGS WERE DRILLED AT THE CLIENT DESIGNATED LOCATIONS
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY BORINGS ARE PLOITED TO DEPTH.
4. THE EXPLORATORY BORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE
DEGREE IMPLIED BY THE MEÏHOD 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 THE BORINGS AT THE TIME OF DRILLING
7. LABORATORY TEST RESULTS:
Wc = wATER CONTENT (%) (ASTM D2216);
DD = DRY DENSITY (pcf) (ASTM D2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913);
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM Dl140);
LL = LIQUID LIMIT (ASTM D4318):
PI = PLASTICITY INDEX (ASTM 04318).
18-7 -692 Kumar & Associates LEGEND AND NOTES Fig. 3
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DIAMETER OF
2,OIN MILLIMETERS
CLAY TO SILT COBBLES
GRAVEL 57 % SAND
LIQUID LIMIT
SAMPLE OF: Sìlly Sondy Grovel
2A%
PLASTICITY INDEX
SILT AND CLAY
FROM:Borlngl@20'
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DIAMETER OF FARTICLES IN MILLIMETERS
CLAY TO SILT COBBLES
GRAVEL 30 % SAND
LIQUID LIMII
SAMPLE OF: Silty Sond qnd Grovel
55%
PLASTICITY INDEX
SILT AND CLAY 17 %
FROM:Boring2O15'
'fh.s€ tscl rssulls opply only lo lhe
sompl€! whlch wore lolltd. Th€
lcsllng rcport sholl nol bc reproduc.d,
€xc€pl fn full, wllhoul lhe wrlllçn
opprovql of Kumor & Âssoolofes, lno.
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occordonc€ wlth ASTM D6915, ASTM D792E,
ASTM C156 ondlor ASÍM D|140.
SIEVE ANÂLYSISHYDROMETER ANALYSIS
IIME NüDINçS
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U.5. STANDARD SERIES CLEAR SQUAFE OPENINOS
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MEDIUM ICOARSE FIN E COARSEFIN E
HYDROMETER ANALYSIS SIEVE ANALYSIS
CLEAR SOUARE OPENINCSI¡UE REÀOINCS
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U.S. SIANDARD SÊRIES
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FIN E MEDIUM CÔARSE FINE COARSE
GRADATION TEST RTSULTS Fig. 418-7 -692 Kumar & Associates
rcrf irffih:ffi:ËH1"'Ëü**'TABLE 1SUMMARY OF LABORATORY TEST RESULTSPNo.18.7.692Clayey Sandy GravelSOIL TYPEGravelly SandySilty SandsikCUNCONFINEDCOMPRESSIVESTRENGTH(olrlPLASTICINDEXATTERBERG LIMITS(ololLIQUID LIMITPERCENTPASSING NO.200 srEvESAND(%)GRADATION(%)GRAVELNATURALDRYDENSITYlocfl(%lNATURALft|OISTURECONTENT(ft)BEPTHSAMPLE LOCATIONBORING1318957.52t/z-354JJ54I16.s9.52t/z-34y,