HomeMy WebLinkAboutSubsoil StudyI(t,THffiåffiffiiiï:-*"
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'cotn
Office l¡cations: Denver (HQ), Parker, Colorado Springp, Fort Collins, Glenwood Springs, and Summit Cotmty, C-olorado
PRELIMINARY STJBSOIL STUDY
FOR FOUI\IDATION DESIGN
PROPOSED RESIDENCES
LOTS I - 4,BLOCK 1 AI{D LOTS t - 4,BLOCK 2
TTIE FAIRWAYS, BATTT,EMENT MESA
IIOGAIY CIRCLE
GARFIELD COUNTY, COLORADO
PROJECT NO.2l-1-229
JIILY 21,2021
PREPARED FOR:
VINCENT TOMASULO
c/o RUSSELL CARTIVRIGHT
35 U/ILLOW\rIEIV }VAY
PARACTTUTE, COLORADO 81635
russecart@gmail.com
T^A.BLE OF'CONTENTS
PURPOSE Al.{D SCOPE OF STUDY 1
2-
3
3-
J-
4-
5-
5-
6-
PROPOSED CONSTRUCTION I
SITE CONDITIONS.....I
FIELD ÐCLORATION
SUBSURFACE CONDITIONS
FOTINDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS ........
FOUNDATIONS
FOUNDATION AND RETAINING IÙI/ALLS
FLOOR SLABS.....
UNDERDRAIN SYSTEM
SURFACE DRAINAGE.
LrMrTATrONS...............
FIGURE I . LOCATION OF ÐGLORATORY BORINGS
FIGURE 2 . LOGS OF ÐGLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
6-
FIGLJFiE 4 through 6 - SÏVELL-CONSOLIDATION TEST RESULTS
FIGURE 7 - GRADATION TEST RESULTS
TABLE I- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Asooclates, lnc. o Pmjec'l No.2t-7-229
PI]RPOSE Ä,ND SCOPE OF'STUDY
This report presents the results of a preliminary subsoil study for proposed rcsidences to be
located on Lots I to 4, Block I and Lots I to 4,Block Z,The Fairways, Battlement Mes4 Hogan
Circle, Garfield County, Colorado. The project siæ is shown on Figure 1. Thç purpose of the
study was to develop preliminary recommendations for foundation designs. The study was
conducted in accordance with or¡r agreement for geotechnical engineering services to Russell
Carturright dated March 1,2021.
A freld exploration prograrn consisting of exploratory borings was conducted to obtain
information on the subsurface conditions, Sarrples of the subsoils obt¿ined during the field
exploration were tested in the laboratory to determine their classification, comprossibility or
swell and other engineering characteristics. The results ofthe field exploration and laboratory
testing were analyzed to develop recommend¿tions for foundation t]æes, depths and allowable
pressures for the proposed building foundation. This report surnmarizes the data obtained during
this study and preselrts our coüch¡sions, design recommendations and other geotechnical
engineering considerations based on the proposed construction and the zubsurface conditions
encountered'
pRopos*r) coNsrRucrroN
The proposed residences will be one- and two- story sfiuctures with attached garages. Ground
floors will be süuctural over crawlspace for the living areas and slab-on-grade for the garage.
Grading for the stnrchrres is assumed to be relatively minor with cut depths between about 2ta 5
feet. We assume relatively tight foundation loadings, typical of the proposed type of
construction,
If building loadings, location or grading plans change significantþ from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The subject site was vacant at the time of our fietd exploration. The ground surface is sloping
down to the east at an estimated grade of about l0 percent. Vegetation consists of grass and
sparse wçeds.
Kumar & Asgoclates, lnc. o Project l{0.21-7-229
I
-2-
FIELD EXPLORATION
The field exploration for the project was conducted on March 26,2021. Four exploratory
borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions.
The borings were advanced with 4-inch diameter continuous ftight augers powered by a truck-
mounted CME45B drill rig. The borings were logged by a representative of Kumar &
Associates,Inc.
Samples of the subsoils were taken with l%-inch and 2-inch I.D. spoon samplers. The samplers
were driven into the subsoils at various depths with blows from a 140-pound hammsr falling 30
inches. This test is similar to the ståndard penetration test desøibed by ASTM Method D-1586.
The penefration resistance values are an indication of the relative density or consistency of the
subsoils. Depths at which the samples rü¡ere taken and the penetration resistanoe values are
shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our
laboratory for review by the project engineer il¡d fs5ring-
ST]BSURFACE CONDIÎIONS
Graphic logs of the subsurface conditions encountered at the site a¡e shown on Figure 2. The
subsoils consist of about 1 foot of topsoil mainly sandy silt soils to depths between
12 and 20 feet whcre dense, siþ clayey sand and gIavel with cobbles was encountered to the
maximum explored depth of 24 feetdeep. Drilling in the dense granular soils with auger
equipment was difficult due to the cobbles and possible boulders and drilling tefusal was
encountered in tbe deposit at Borings 1 and 4.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and gradation analyses. Results of swell-consolidation testing performed on
relatively undist¡rbed drive samples of the silt soils, presented on Figures 4 througb 6, indicate
low compressibitity under existing low moisture conditions and light loading and varied low
collapse to low swell potential when wetted under constant light surcharge. Results of gradation
analyses performed on small diameter drive samples (minus l%-nchfraction) of the coarse
granular subsoils are shown on Figure 7. The laboratory tÊsting is summarized in Table l-
No free water was encowrtered in the borings at the time of dritling and the subsoils were
slightþmoist.
Kumar & Assoclates, lnc. e Project No. 21-f -225
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FOTI¡IDATION BEARING CONDITIONS
The upper silt soils encountered in the borings possess low bearing capacíty and varied
compression/expansion potential when wetted. Our experience indicated the upper fine-grained
soils are mainly compressible when wetted under loading. The underlying gravel soils possess
moderate bearing capacity and typically low settlement potential. Spread footings placed on the
upper fine-grained soils can be used for support of the proposed residences with a risk of
foundation movement. A lower risk optiol would be to extend ths beartng level down to the
underþing gravel soils with a deep foundation system such as drilled piers or micro-piles.
Provided below are recommendations for a spread footing foundation system. If
recommondations for a deep foundation system are desired, we should be contacted to provide
them.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encor¡ntered in the exploratory borings and the nature of
the proposed construction, we recommend the building be formded with spread footings bearing
on the natt¡ral fine-grained soils.
The design and construction sriteriapresented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural fure-grained soils should be desþed
for an allowable bearing pressure of 1,500 psf. Based on experience, we expect
initial settlement of footings designed and constructed as discussed in this seotion
wilt be about 1 inch or less. Additional post-construction differential foundation
movement could occt¡r if the bearing soils becone wetted. The magnitude of
additional movement would depend on the depth and extent of wetting but could
be on the order of about L to lYz inohes.
Z) The footings should have a minimum width of l8 inches for continuous walls and
2feet for isolated Pads.
3) Exterior footings and footings berieath 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 found¿tion walls should be heavily reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 14 feet.
Kumar &Associate¡, lnc. o Profec.t No. 21-7-225
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Foundation walls acting as retaining structures should also be designed to resist
lateral earttr pressures as discussed in the "Foundation and Retaining Walls"
seçtion of this rePort.
Topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the firm natural fine-grained soils. The exposed
soils in footing area should then be moistened and compacted-
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 strr¡ch¡res 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 fïne-grained soits- Cantilevered retaining süuctures which are separate from the
residences and can be expected to deflect sufficientþ to mobilize the fuIl active earth pressure
condition shouldbe designed for a lateral earthpressure computed on the basis of an equivalent
fluid unit weight of at least 45 pcf for baclcfill consisting of the on-site fine-grained soils.
A1l foundation aûd retaining stn¡ctures shouldbe designed for appropriate hydrostatic and
surcharge press¡res such as adjacent footings, traffic, construction materials and equipment' The
pressures rsoommsnded above assume drained cotrditions behind thc 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 stucture. An underdrain
should be provided to prevent hydrostatic pressure buildup behind walls.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard proctor density at a moisture content near optimum. Backfill placed in pavement and
wallr:way areas should be compacted to at leastglo/a 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 ifthe material is placed corectþ, and could result in distress to
facilities constucted on thc backfill'
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resistance of the footing on the foundation materials andpassive earth pressure against
the side of the footing. Resist¿nce to sliding at the bottoms of the footings can be calculated
based on a coefficient of ûiction of 0.35. Passive pressure of compacted backfill against the
5)
6)
Kumar & Associates, lnc. @ Proiec{ No.2t-7-229
5
sides of the footings can be calculated using an equivalent fluid unit weight of 350 pcf. The
coefücient of friction and passive pressure values recommended above assume ultimate soil
stuength. Suitable factors of safety should be included in the desþ to limit the shain which will
occur at the ultimate strengt\ particulady in the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads should be compacted to at Least95o/" of the
maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suit¿bte to support lightly loaded slab-on-grade
construction with a risk of movement similar to that described above for 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 reinforeeurent should be est¿blished by the designor based on experience and
the intended slab use. A minimum 4-inch layer of free-draining gravel should be placed beneath
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 2% passing the No. 200
sieve.
All fill materials for support of floor slabs should be compacted to at least 95Yo 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 \ilas not encountered during our exploration, it has been our experience in
the area that local perched groundwater can develop during times of heavy precipitation or
seasonal runoff. Frozen ground during spring runoffcan create a perched condition. 'We
recommend below-grade constn¡ction, such as retaining walls, crawlspace (greaterthan 4 feet
deep) and basement areas (if any), 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 sr¡nounded above
the invert level with free-draining gfanular material. The drain should be placed at each level of
excavation and at least I foot betow lowest adjacent finish grade and sþed at a minimum lYoto
a suitable gravity outlet or sump and pump. Free-draining granular material used in the
underdrain system should cont¿in less than 2% passing the No. 200 sieve, less than 50% passing
Kumar &Astociates, lnc. o Projecl No.2f-7-229
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the No. 4 sieve and have a maximum stze of 2 inches. The drain gravel baclcfill should be at
least lt/zfeet deep. An impervious membrane such as 20 mil PVC should be placed beneath the
drain gravel in a trough shape and att¿ched to the foundation wall with mastic to prevent wetting
of the bearing soils.
SURFACE DRAJNAGE
providing proper surface sading and drainage will be critical to limiting subsr¡rface wetting and
potential buitding movement. The following drainage precautions should be observed during
construction and maintained at all times after the residences have been completed:
1) tnundationofthe foundationexcavations andunderslab areas shouldbe avoided
during construction.
Z) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95% of the maximum standa¡d Proctor density in pavement and slab areas
and to at least 90% of the maximum staûdåxd Froctor density in landscape afeas'
3) The ground surface sunounding the oxterior of the building should be sloped to
drain away from the foundation in alt directions. We recommend a minimurn
slope of 12 inches in the first 10 feet in unpaved areas and a minimum slope of
3 inches in the first l0 feet in paved af,eas. Freedraining 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 inigation should be located at least 10
feet from foundation walls. Consideration should be given to the use of xeriscape
to limit potential wetting of soils below the foundation caused by inigation.
LINIITATIONS
This study has been conducted in accordance with generally accepted geotechnical eugineering
principles and practices in this arcaatthis 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 l, the proposed tlfc of
construction and our experience in the area. Our services do not include determining the
presence, prevention or possibility of mold or other biological sont¿minaûts (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 ñndings include interpolation and extrapolation of the
Kumar & A¡sociatos, lnc. o Project l{o. 21:l-229
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subsr¡rface conditions identified at the exploratory borings and væiations in the subsurface
conditions may not become evident until excavation is performed. If conditions e,lrcountered
during constn¡ction appear different from those described in this rqport, we should be notified so
that re-evaluation of the recommendations may be made.
This report has been prepared for the exclusive use by or¡r client for planning and preliminary
design purposes. We are not respoûsible for technical interpretations by others of our
information. As the project evolves, we should provide continued consultation and field serviccs
during construction to review and monitor the implementation of ourrecommendations, and to
veriff that the recomme,ndations have been appropriately interpreted. Significant design changes
may require additional analysis or modifications to the recommendations presented herein. Vfe
recommend on-site observation of excavations and foundation bearing stata and testing of
stnrctural fill by a relresentative of the geotechnical engineer.
Respectfully Submitted,
Kumar & Associates, Inc"
James H. Parsons, P.E.
Reviewed by:
Steven L. Pawlak, P.E.
JHP/kac
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Kumar & Associates, lnc. ?"Project No. 21-7-229
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BORING 4
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Fig. 1LOCATION OF EXPLORATORY BORINGSKumar & Associates21 *7 -229
BORING 1 BORING 2 BORING 3 BORING 4
0 2e/12
WC=4.8
DD*98
-2OO=92
o
19/ 12 45/12
WG=5.7
DD=107
5
22/12
WC=5.8
DD=1Ol
26/12
28/1?
WG=3.8
DD=1 04
ss/12
18/12
WC=4.0
DD=l O3
5
24/12
23/12 23/12 24/12
10 10
24/12 22/12
WC=4.3
DD=99
24/12
WC=6.4
DD=99
25/12
WC=4.8
DD=l 09
15
25/6, ,O/s
WC=4.6 15
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31 /12
WC=5.5
DD=l 1 5
-200=94
40/12 e2/12 +4=26
-200=45
zo 20
43/12 50/1 50/2
25 25
30 30
21-7-229 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
I
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TOPSOIL: SILT' SANDY, ORGANICS, FIRM, SLIGHTLY MOIST' BROWN'
stLT (ML): SLIGHTLY SANDY TO SANDY, SANDTER WITH DEPTH, SLIGHTLY CLAYEY, SLIGHTLY
CALCÀREôUS, VERY STIFF TO I{ARD, SLIGHTLY MOIST' TAN.
GRAVEL (CC-CU): SANDY, SILTY, CLAYEY, COBBLES, POSSIBLE BOULDERS, DENSE, SLIGHTLY
MOIST, GREY BROWN.
DRIVE SAMPLE, z-INCI.I I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE, 1 S/A-INCH l.D. SPLIT SPOON STANDARD PENETRATION TEST-
.^1.^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 49 BLOWS OF A l4O-POUND HAMMER
'4r/ t¿ rtùr-ñC sólñcttÈS wERE REQUIRED To oRIVE THE SAMPLER 12 INCHES.
I enacrrcAL AUcER REFUSAL.
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NOTES
1. TI.IE EXPLORATORY SORINGS WERE DRILLED ON MARCH 26, 2021 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 PLAN PROVIDED.
3. THE ELEVATIONS OF THË EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS ARE
PLOTTED TO DEPTH.
4. THE EXPLORATORY BORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO TI{E
DEGREE IMPLIED BY THE METHOD USECI.
5. THE LINES 8ETÏ/EEN MATERIALS SHOWN ON T¡{E EXPLORATORY BORING LOGS REPRESENT ÏHE
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 (pct) (lSru t2216);
+4 = PERCENTAGE RÈTA¡NED ON NO. 4 SIEVE (ASTM 06915);
-200= PERCENTAGE PASSING NO. 20o slEvE (ASTM 01140).
21-7-229 Kumar & Associates LEGEND AND NOTES Fig. 3
SAMPLE OF: Sondy Sllt
FROM:Boringtg4'
WG = 3.8 %, DD = 1Ol Pcf
NO MOVEMENT UPON
WEfiING
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t00PRESSURE -1.0
1.0
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SAMPLE OF: Silt ond Cloy
FROM:Bortngl@15'
WC = 5.5 %, ÐD = 115 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
21-7-229 Kumar & Associates SWTLL-CONSOLIDATION TEST RESULTS Fig. 4
I
I
à
SAMPLE OF: Sondy Silt
FROM:Boring2(å 2.5'
WC = 5.7 %, DD = 107 pcf
ADDITIONAL COMPRESSION
UNDËR CONSTANT PRESSURE
DUE TO WEÏTING
1
0
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=tn
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- KSF t01,01
,I APPUED
SAMPLE 0F: Sondy Silt
FROM: Boring 2 @ 10'
WC = 4.3 %, DD = 99 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
Fig. 5SWELL-CONSOLIDATION TEST RTSULTS21-7-229 Kumar & Associates
SAMPLE OF: Sondy Silt
FROM:Boring3O4'
WC = 3.8 %, DD = 104 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
às
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PRESSURE -t
SAMPLE OF: Sondy Silt
FROM:Boring4@10'
WC = 4.8 %, DD = 1O9 pcf
ËXPANSION UNDER CONSTANÏ
PRESSURE UPON WETTING
21*7-229 Kumar & Associates SWELL-CONSOLIDATION TEST RTSULTS Fig. 6
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I(l'TKumr & Associates, lnc."Geotechnical and Materials Engineersand Environmental ScientistsTABLE 1SUMHARY OF LABORATORYTEST RESULTSSlightly Sandy SiltSandy SiltSandy SiltSandy SiltSandy SiltSilty Clayey Sand andCravelSandy SiltSilt and ClaySandy SiltSandy Siltsot Tï?Elosllrs{coilFNEoCONPRESSIESTRËIIGTHPLASTIC[{DEXr%tAÏTERBERG LMTS$tLH'þI."HÍT9243PERCENTPASSIIGr*0.200 sEvE94I3f/6)SAND26GRADATION(%)GRAVET10111510799981M99103109I{AÏT'RATDRYDËI¡SITYlocll4.84.6t%tNÀTURAtrotsTt REcü{rEllÎ3.85.55.74.34.83.86.44.00150I4I45I2t/,l0I4tftìDEPTH2J4BORI}¡G1