HomeMy WebLinkAboutSubsoil Study 10.19.2021lClIåitir,ffi:;"fÉ:in'"'Êü*'*
An Employcc 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
Ofñce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR F'OUNDATION DESIGN
PROPOSED RESIDENCE
2808 COUNTY ROAD 117
GARFIELD COUNTY, COLORÄDO
PROJECT NO. 18-7-692
ocToBER 19,2021
PREPARED FOR:
DM NEUMAN CONSTRUCTION
ATTN: JASON NEUMAN
P.O. BOX 2317
GLENWOOD SPRINGS, 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 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Associates, lnc. @ Project No. 18-7-692
PURPOSE AND SCOPE OF STUDY
This report presents the results of a 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 purpose of the sfudy was to develop recommendations for the foundation design.
The study was conducted as additional services to and in accordance with our agreement for
geotechnical engineering services to DM Neuman Construction dated November 13, 2018.
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 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, design recommendations and other geotechnical engineering considerations based
on the proposed construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
Design plans for the residence were in progress at the time of our study. The proposed residence
will be a wood-frame structure located as shown on Figure 1. Ground floor will be structural
over crawlspace in the residence and slab-on-grade in the garuge. 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 CONDITIONS
The ground surface in the building area is relatively flat with a gentle slope down to the north
and a few feet of estimated elevation difference. The site is a small valley bottom with a steep
hillside to the east and moderate slope to the west. The building site was disturbed and filled 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. @ Project No. l8-7-692
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F'IELD EXPLORATION
The f,reld exploration for the project was conducted on September 1,2021. Three exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions.
The borings were advanced with 4-inch diameter continuous flight augers powered by a truck-
mounted CME-45B drill rig. The borings were logged by a representative of Kumar &
Associates.
Samples of the subsoils were taken with l% inch and Z-inch I.D. spoon 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 by ASTM Method D-1586,
The penetration resistance values are aî 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 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 encountered consist of about 7 to 13% feet of loose, silty clayey sand with gravel to
sandy silty clay fill overlying medium stiff to stiff silty sandy clay in Borings 1 and 3 and
organic clay in Boring 2 underlain at depths of l}Yz to 18 feet by relatively dense, silty sandy
gravel, cobbles and boulders to the drilled depths of 13% to 26 feet. Drilling in the coarse
granular subsoils with auger equipment was difficult due to the cobbles and boulders and drilling
refusal was encountered in the 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 (minus l%-inch fraction) of the coarse
granular subsoils are shown on Figure 4. The laboratory testing is summarized 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.
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FOUNDATION BEARING CONDITIONS
The fill material encountered in the borings appears 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 fill after complete removal down to the native soils.
Organic soils such as encountered in Boring 2 should be discarded. Structural fill placed up to
footing bearing level throughout the entire building footprint and below driveway and parking
areas should be compacted to at least 98% of standard Proctor density atnear optimum 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
suitability of the existing fill as structural material should be further evaluated at the time of
construction.
DESIGN RACOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded with spread footings 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 risk, we should be contacted for
additional analysis and recommendations.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed or ?o-pu"t"d rt*"t rtul ftll thgnld be designed for an allowable
bearing pressure o?þf. Based on experience, we expect initial settlement
of footings designed and constructed as discussed in this section will be about I
inch or less. Additional long-term settlement could be around lYo of the fill depth
or about I to 2 inches for possible fill depths of 10 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 frost protection. Placement
of foundations at least 36 inches below exterior grade is typically used in this
area.
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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. If soft soils are encountered, the
subgrade should be stabilized before fill placement.
A representative of the geotechnical engineer should evaluate structural fill
compaction on a regular basis during placement and observe all footing
excavations prior to concrete placement for bearing conditions.
FOT]NDATION 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 50 pcf for backfill 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 40 pcf for backfill consisting of the on-site soils. Backfill should not contain organics,
debris or rock larger than about 6 inches.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The
pressures recommended 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 imposed on a foundation wall or retaining structure. An underdrain
should be provided 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 atnear optimum moisture content. Backfill placed in pavement and
walkway areas should be compacted to at least 95Yo of the maximum standard Proctor density.
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. Some settlement of deep foundation wall
backfill should be expected, even if the material is placed correctly, and could result in distress to
facilities constructed on the backfill.
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The lateral resistance of foundation 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 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 recommended above assume 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
the sides of the footings to resist lateral loads should be compacted to at least 95Yo of the
maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
Structural fill soils placed as part of the building site development are suitable to support lightly
loaded slab-on-grade construction with a settlement risk similar to footings. 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 interior slabs for subgrade. This material should consist of
minus 2-inch aggregate with at least 50%o retained on the No. 4 sieve and less tharr l2Yo passing
the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95Yo of maxlmum
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 develop during times of heavy
precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched
condition. We recommend below-grade construction, such as retaining walls, crawlspace and
basement areas, 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
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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 2o/opassingthe No. 200 sieve, less than 50% passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least llz feet deep. An
impervious membrane such as 20 mll 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 improvements. 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 95%o 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 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 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
from the exploratory borings drilled at the locations indicated on Figure 1, the proposed type of
construction and our experience in the arca. Our services do not include determining the
presence, prevention or possibility of mold or other biological contaminants (MOBC) developing
Kumar & Associates, lnc. @ Project No. l8-7-692
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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 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 recommendations, 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:
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Daniel E. Hardin, P.E.
SLP/kac
cc: DM Neuman Construction- Rich Carter (richrliglltlrç1¡4al1.ciuu)
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Kumar & Associates, lnc. i Project No.18-7-692
2808 CR 117
NOT TO SCALE
18-7 -692 Kumar & Associates LOCATION OF EXPLORAÏORY BORINGS Fig. 1
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12/12 s/12 5/12
5 57/12 13/12 7 /12
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WC=17.8
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-2OO=79
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+4=30
-2OO=17
20 62/12
WC=4.6
*4=57
-200= 1 5
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25 2550/o
30 30
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WC=13.1
-2OO=49
LL=21
Pl=2
18-7 -692 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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LEGEND
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FILL: 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, MOIST, BROWN.
ORGANIC CLAY (CL); SILTY, SANDY, SOFT, VERY MOIST, GRAY-BROWN
GRAVEL, COBBLES & BOULDERS (OU); SII-IV, 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, '.t 3/1-|NCH l.D. SPLIT SPOON STANDARD PENETRATION TEST
- r.^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 7 BLOWS OF A 140-POUND IJAMMER'/ '' FALLTNG Jo TNcHES wERE REQUTRED To DRrvE THE sAMpLER r2 rNcHEs.
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 PLOTTED TO DEPTH.
4. THE EXPLORATORY BORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE
DEGREE IMPLIED BY THE 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 THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);
DD = DRY DENSTTY (pcr) (nSrV D2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ISTU OOEIS);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM 01140);
LL = LIQUID LIMIT (ASTM D4518);
PI = PLASTICITY INDEX (ASTM 04518).
18-7 -692 Kumar & Associates LEGEND AND NOTES Fig. 3
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DIAMETER OF INM RS
CLAY TO SILT COBBLES
GRAVEL 57 % SAND
LIQUID LIMIT
SAMPLE OF: Sllty Sondy Grovêl
28%
PLASTICITY INDEX
SILT AND CLAY 15 %
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DIAMETER OF IN
CLAY TO SILT COBBLES
GRAVEL 30 % SAND
LIQUID LIMIT
SAMPLE OF: Sllty Sond ond Grovel
55%
PLASTICITY INDEX
SILT AND CLAY 17 %
FROM:Borlng2O15'
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occordonc. wllh ASTI D6915, ASTM 07928,
ASTM Cl56 ondlor ASTM Dll.l0.
SIEVE ANALYSISHYDROMETER ANALYSIS
TIHE RUDINôS
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SIEVE ANALYSISHYDROMETER ANALYSIS
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18-7 -692 Kumar & Associates GRADATION TEST RESULTS Fig. 4
lGrtii':;1f;'åifffifn'""3ü'**TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo. 18-7-692SOIL TYPEGravelly SandyClavev SiltSilty SandClayey Sandy GravelGilr)(psf)UNCONFINEDCOMPRESSIVESTRENGTHPLASTICINDEX("/"1ATTERBERG LIMITSLIQUID LIMITloÂlPERCENTPASSING NO.200 stEVE54aa-) -)SAND(%)a-t1GRADATIONGRAVELl:/"18154NATURALDRYDENSITYlocfì95P/"1NATURALMOISTURECONTENT6.59.57.5DEPTHBORING2Vr-34y,2r/r-3SAMPLE LOCATIONI2