HomeMy WebLinkAboutSubsoil Study for Foundation Design 09.14.18H.PVKUMAR
Qegtechnlcal Engineering I Engineering Geology
Maþrlals Testlng I Environmental
5020 County Road 154
Glenwood Springs, CO 91601
Phone: (920) 94S-79S8
Fax (970) 94S-84S4
Email : hpkglenwood@kumarusa.com
Office Locations: Denver (HQ), Parker, colorado springs, Fort collins, Glenwood springs, summit county, colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 55, PINYON MESA
GARFIELD COUNTY, COLORADO
PROJECT NO. 18-7-53s
SEPTEMBER 14,2018
PREPARED FOR:
INTEGRATED MOUNTAIN DEVELOPMENT INC.
ATTN: JIM GORNICK
P.O. BOX 908
GLENWOOD SPRINGS, COLORADO 81602
.i im.sornick @ intesratedmtn.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS ,..
SUBSIDENCE POTENTIAL
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 - LF,GEND AND NOTES
FIGURES 4 and 5 - SWELL-CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
1
1
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H.PVKUMAR
Project No. 18-7-535
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Paintbrush Way, Lot 55, Filing 2,Pinyon Mesa, 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 Integrated Mountain Development, Inc. dated Augu st22, Z0lg.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils and bedrock 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 werc 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 encouuteretl.
PROPOSED CONSTRUCTION
The proposed residence will be a I to 2 story structnre over a walkout basement with attached
garage and located as shown on Figure 1. Ground floors will be slab on grade. Grading for the
structure is assumed to be relatively minor with cut depths between about 3 to 8 feet, We
assume relatively light foundation loadings, typical of the proposed type of construction.
Ifbuilding 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
Thc subject site was vacant at the time of our fieltl exploration. The ground surface is sloping
down to the west at a grade of around l5%o. Elevation difference across the building area is
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Prolect No. 18-7-535
a
about 10 feet ancl across the lot is about 20 feet. Vegetation consists of grass, weeds, sagebrush,
and small pinyon pines.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the subject site. These rocks
are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds
of gypsum and limestone. There is a possibility that massive gypsum deposits associated with
the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the gypsum under certain
conditions can cause sinkholes to develop and can produce areas oflocalized subsidence.
During previons work in the area, sinkholes have been observed scattered throughout the lower
Roaring Fork Valley. These sinkholes appeff similar to others associated with the Eagle Valley
Evaporite in this area.
Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities
was encountered in the subsurfacc materials; howcver, the exploratory borings were relatively
shallow, for foundation design only. Based on our present knowledge of the subsurface
conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of
futttre ground subsidence on Lot 55 throughout the service life of the proposed residence, in our
opinion, is low; howevet, the owner should be made aware of the potential for sinkhole
development. If further investigation of possible cavities in the bedrock below the site is desired,
we should be contacted.
FIELD EXPLORATION
The field exploration for the project was conducted on August 27 ,20L8. Two exploratory
borings wele 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-458 drÌll rig. The borings were logged by a representative of H-P/Kumar.
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
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subsoils and hardness of the bedrock. 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 consist ofabout 1 foot oftopsoil overlying 4Yzto27 feetofsandy to very sandy silt and
clay to sandy clay with gravel. Siltstone of the Eagle Valley Evaporite was encountercd at 5vz
feet in Boring 2 and ar.28 feet in Boring 2.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and finer than sand size gradation analyses. Results of swell-consolidation
testing performed on relatively undisturbed drive samples, presented on Figures 4 and,5,indicate
low compressibility unde¡ conditions of light loading and natural moisture content then variable
collapse or expansion when wetted.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
FOUNDATION BEARING CONDITIONS
The natural sandy silt and clay soils within about the upper 5 to 7 feet are low density and highly
compressible. The underlying soils possess low bearing capacity and variable swell or
settlement potential mainly when wetted. The siltstone bedrock materials encountered below the
soils possess moderate bearing capacity and low settlement potential. At assumed excavation
depths we expect the subgrade will expose sandy silt and clay soils and siltstone bedrock.
Excavations of less than 5 feet in depth may need to be deepened to expose less compressible
soils and the sub-excavated depth backfilled with structural fill. Spread footings should be
feasible for foundation support of the residence with a risk of differential movement due to
variable bearing conditions. A low settlement risk option would be to extend the foundation
bearing level down to the bedrock with a deep foundation system such as micro-piles or helical
piers.
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Project No. 18-7-535
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DESIGN RECOMMENDATIONS
FOUNDATIONS
The following design recommendations are for a spread footing foundation system. If design
recommendations for a lower risk, deep foundation system are desired we should be notified to
provide those.
The design and construction criteria presented below should be observed for a sprcad footing
foundation system.
1) Footings placed on the undisturbed natural soils below a depth ofaround 5 to T
feet or bedrock should be designed for an allowable bearing pressure of 1,200 psf.
Footings placed entirely on bedrock can be designed fol an allowable bearing
pressure of 2,500 psf. Based on experience, we expect initial settlement of
footings designed and constructed as discussed in this section will be about 1 inch
or less with about Vzto I inch of additional differential settlement if the bearing
soils ale wetted.
2) The footings 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 providecl 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 and especially across the soil/bedrock transition area, such as by
assuming an unsupported length of at least 12 feet. Foundation walls acting as
retaining stl'tlctures should also be designed to resist lateral earth pressures as
discussed in the "Foundation and Retaining Walls" section of this report.
5) The topsoil, low density material (upper 5 to 7 feet) and any loose disturbed soils
and rock should be removed and the footing bearing level extended down to the
firm natural soils or bedrock. The exposed soils in footing area should then be
moistened and compacted. Stntctural fill placed below footing areas can consist
H-PV(UMAR
Project No. 18-7-535
5
of the onsite soils compacted to at least 98Vo of standard Proctor density at near
optimum moisture content and to at least rvz feet beyond the footing edges.
A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOUNDATION AND RETAINING WALLS
Foundation walls and retaining structnres 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 backfill consisting
of the on-site fine-grained 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 45 pcf for backfill consisting of the on-site fine-grained soils.
All foundation and retaining structures shor,rld 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 wali or an upward sloping backfill s'rface will
increase the lateral plessure 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 riniform lifts and compacted to at least 90Vo of the maximum
standard Proctor density at a moisture content near optimum. Backfill placed in pavement and
walkway areas should be compacted to at least 95Vo of the maximum standard Procto¡ 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. Backfill should not contain organics, debris or rock larger
than about 6 inches.
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
6)
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Project No. 18-7-535
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the sicle 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 backfìll against the
sides of the footings can be calculated using an equivalent fluid unit weight of 350 pcf. The
coefficient of f¡iction 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, particuiarly in the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads should be a nonexpansive material compacted to at
least957o of the maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab-on-grade
construction with a settlement risk mainly if the bearing soils are wetted. 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 free-draining gravel should be placed beneath
basement level slabs fo facilitate drainage. This material shoriid consist of minus 2 inch
aggregate '"vith at least 50Vo retained on the No. 4 sieve and less than 27o passing the No. 200
sieve.
All fill materials for support of floor slahs should be compactecl to at least 95To of maximum
standard Proctor density at a moisture content near optimum. Requirecl fill can consist of the on-
site soils devoid ofvegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area and where there are clay soils and shallow bedlock that local perched groundwater can
develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring
rrinoff can create a perched condition. We recommend below-grade construction, such as
retaining walls and basement areas, be protected from wetting and hydrostatic pressure buildgp
H.PryKUMAR Project No. 18-7-535
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by an underdrain system. An underdrain should not be placed around shallow crawlspace areas
to help limit the potential for wetting the bearing soils.
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 1 foot below lowest adjacent finish grade and sloped at a minimum IVo to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 27o passing the No. 200 sieve, less than 507o passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least IVz feet deep. An
impervious membrane sttch 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
Proper surface grading and drainage will be critical to keeping the bearing soils dry and limiting
potential diffelential foundation settlements. The following drainage precautions should be
observed dr"rring construction and maintained at all times after the residence has been completed:
1) Inundation ofthe foundation excavations and underslab areas should be avoided
dr-rring construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 957o of the maximum standard P¡octor density in pavement and slab areas
and to at least 907o of the maximum standard Proctor density in landscape areas.
3) The gror.rnd 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 weli beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation should be located at least 10
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.
H-PVKUMAR Project No. 18-7-535
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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
f¡om the exploratory borings drilled excavated 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 ofthe 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 continued consultation and field services during construction to review and
monitor the implementation of our recommendations, and to verify 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,
H-P+KUMAR
James H. Parsons, E.I.
Reviewed by:
Steven L. Pawlak,
JHPlkac
Project No. 18-7-535
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BORINC f
EL. 6204'
BORING 2
EL. 521 1'
0 0
6/ 12
3/12
WC=4.4
DD=9 I
5 57/12
WC=4.5
DD=92
21/12
t0 t01s/ 12
WC=5.6
DD= 1 02
-200=7 1
so/3
f5 15Ft!UL!
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27/12
WC=5.4
DD=1 13
so/ 1 FLd
t!l"!
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20 2021/12
¿a 2528/12
WC=2.6
DD= 1 02
-2OQ=75
30 3043/12
35 35
1 8-7-53s H.PryKUMAR LOGS OF EXPLORATORY BORINGS Fig. 2
LEGEND
NI
þ! ToPSolL; SILTY sAND AND GRAVEL wtrH SCATTERED coBBLES, Morsr, BRowN, Roor zoNE.N
9I|I å!P.-C-q!-(ML-CL);--S¡NDY, sLIGHTLY To. MoDERATELY cALcAREoUs, soFT îo STIFFAND VERY STIFF WITH DEPTH AT BORING I, SIrCrrÍiY-úóîir, iiîilV'N" rO U¡¡.
SAND AND CLAY (sc-cL); srlrv, scATTERED cRAvEL, MEDTuM DENsE, sLrcHTLy Morsr, TAN
SILTSTONE BEDROCK; SOME GYPSUM, MEDIUM HARD To VERY HARD WITH DEPÏH, SLIGHTLYMOIST, WHITE TO GRAY. EAGLE VALLEY EVAPORITE
RELATIVELY UND|STURBED DRIVE sAMpLE; 2-|NCH t.D. cALtFoRNTA LTNER sAMpLE.
ozt z pf[e*.'1ffli.T'.1*',i.'#-l¡dü?ÄEå'i:
'JliJ,'r,îå'å'fr,r%rf,^'th??!H', iiixñE..
NOTES
1. THE EXPTORATORY BORINGS WERE DRILLED ON AUGUST 27,2018 WITH A 4-INCH DIAMETERCONTINUOUS FLIGHT POWER AUGER.
2' ÏHE LOCATIONS OF THE EXPLORATORY BOR1NGS WERE MEASURED AppROXtMATELy By TAptNGFROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED 8Y INîERPOLATION BETWEENCONTOURS ON THE SITE PLAN PROVIDED.
4. ÏHE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATEONLY TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THEAPPROXIMATE BOUNDARIES BETWEEN MATERIAL wÞÈs-Ãrlo rsË rnrruslloNs MAy BE GRADUAL.
6' GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:wc = wATER CÕNTENT (%) (ASTM D 2216);DD = DRy DENS|Ty (pcf) (ASTM D zzts)i
-20a= PERCENTAGE pASStNc No. 200 srÈve llsru D 1140).
n
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n
n
1 8-7-535 H-PryKUMAR LEGEND AND NOTES Fig, 3
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d
SAMPLE OF: Sondy Cloy wilh Grovel
FROM: Boring 1 @ 15'
WC = 5.4 %, tD = 11J pcf
EXPANSION UNDTR CONSTANT
PRESSURE UPON WETTING
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lh.!6 t.st rclull! oppry oñty to thc!ôñpìá iê!t.d. lh€ t.sli¡q ¡.eortrholl not bê r.produc.d, .xc¿Þt ;ñ
tull, withovt lh. ,'itt6. opÞroiot ot
Kumo. dnd tulociol!!, ldc. Sslll
CoÂtolidotion t.diñq p.dom.d ¡no.cordo¡c! fith m 0-4548.
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=ln
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fo
U)zo(J
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-t
1.0 APPLIEO P - KSF 100
1 8-7-535 H.PryKUMAR SWELL-CONSOLIDATION TEST RESULTS Fig.4
.,i
SAMPLE 0F: Sondy Ctoyey Sitf
FROM:Boring2@2.5
WC = 4.4 %, DD = 91 pcf
I-f
I +
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
)i
I
I
I
I
lh!!c lld .€!ult! opply o¡ly to th!sompllt t!!Ì.d. lhr t.!tí¡E râlod
shdll ñot b6 rcproduc.d. 6¡ccÞt rn
lul¡, wiüout thc rdlt!ı .pprovôr ol
Kumor ond &rociol!!. lñc. Sw.lr
Conlolidotio^ t.iling p.dormcd íuoccordd¡.. H¡lh Ám D-¡5¡6
2
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JJ
t¡J
=an
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o
Jo(nzo()
-¿
-4
-6
-8
0
-12
-14
1.0 SURE - KSF l0 100
1 8-7-535 H-PryKUMAR SWELL_CONSOLIDATION TTST RISULTS Fig.5
H-P*KUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProjectNo. I8-7-535PERCENTPASSINGNO.200SIEVELIMITSUNCONFINEDCOMPRESSIVESTRENGTHGRAVELSAND(%\LIQUIDLIMITPLASTICINDEX(%)SOILTYPESandy Clayey SiltSandy Clayey SiltSandy Clay rvith GravelSandy Silt and ClaySandy Clayey Silt7I75NATURALMOISTURECONTENTNATURALDRYDENSITYBORINGDEPTHI54.692l05.6r02155.4i13102912.64.4252Yz2