HomeMy WebLinkAboutSubsoil Study for Foundation Design 02.28.2020ELßF- o2-zf - 6b?g
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An Employoc Owrlcd Compony
5020 Cowtty Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax (970) 945-8454
email: kaglenwood@<umarusa.com
wwwkurna¡usa.com
Office L¡cations: Dørver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit Comty, Colorado
SUBSOIL STUDY
F'OR F'OI.INDATION DESIGN
PROPOSED RESIDENCE
LOT 12, F'AIRWAYS AT ASPEN GLEN
TBD GOLDEN BEAR DRIVE
GARFIELD COUNTY, COLORADO
9-7-742
FEBRUARY 28,2020
PREPARED FOR:
GSS PROPERTIES
ATTN: GARY SNOOK
P.O. BOX 3377
BASALT, COLORADO 81621
snookcolorado@smail.com
TABLE OT'CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS
SUBSIDENCE POTENTIAL
FIELD EXPLORATION
STIB SURFACE CONDITIONS
FOI"INDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS
FOUNDATIONS
FLOOR SLABS
TINDERDRAIN SYSTEM ........
SURFACE DRAINAGE
LIMITATIONS
FIGURE 1 - LOCATON OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF E)GLORATORY BORINGS
FIGIIRE 3 - LEGEND AND NOTES
FIGURES 4 and 5 - SWELL-CONSOLIDATION TEST RESULTS
FIGURE 6 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Aseociatos, lnc. o Proisc't No. 19-7:142
PURPOSE AND SCOPE OF STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on
Lot12, Fairways at Aspen Glen, TBD Golden Bear Drive, Garfield County, Colorado. The
proj ect 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 Gary Snook dated December 3 I, 2019 .
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 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
encoturtered.
PROPOSED CONSTRUCTION
The proposed residence will be a two story, wood frame structure with attached garage. Ground
floor will be structural over crawlspace for the residence and slab-on-grade for the garage.
Grading for the structure is assumed to be relatively minor with cut depths between about 2 to
5 feet. We assume relatively light foundation loadings, typical of the proposed type of
construction.
STTE CONDITIONS
The subject site was vacant at the time of our field investigation. There was between 8 and
12 inches of snow cover on the site at the time of our investigation. The ground surface is
relatively flat sloping gently down to the north at a grade of about 2 percent. Elevation
difference across the building area is estimated at around I foot. Vegetation consists of grass
and weeds.
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SUBSIDENCE POTENTIAL
Beclrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen Subdivision
These rocks are a seqLrence of gypsiferous shale, fine-grained sandstone and siltstone with some
massive beds of gypsum and limestone. There is a possibility that massive rypsum deposits
associated wrth the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the
rypsum under certain conditions can cause sinkholes to develop and can produce areas of
localized subsidence. During previous work in the are4 several sinkholes were observed
scattered throughout the Aspen Glen Development. These sinkholes appear similar to others
associated with the Eagle Valley Evaporite in areas of the Roaring Fork Valley.
Sinkholes were not observed in the immediate area of the subject lot. A sinkhole was previously
mapped about 400 feet ea.st of the subject lot. No eviclence of cavities was encountered in the
subsurface materials; however, the exploratory borings were relatively shallow, for foundation
design only. Based on orÌr present knowledge of the subsurface conditions at the site, it cannot
be said for certairt that sinkholes will not develop. The risk of future ground subsidence on
Lot 12 throughout the service life of the proposed residence, in our opinion, is low; however, 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.
F'IELD EXPLORATION
The field exploration for the project was conducted on January 6,2020. Two 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 flight augers powered by a truck-
mounted CME-458 drill rig, The borings were logged by a representative of Kumar &
Associates,Inc.
Samples of the subsoils were taken w'tth I% inch and 2 inchl.D. spoon samplers. The samplers
were driven into the subsoils at various depths wth blows fiom a 140 pound hammer f'alling 30
inches. This test is similar to the standard penetration test described by ASTM Method D-1586
The penetration resistance values are ari indication of the relative density or consistency of the
subsoils. Depths at r¡¡hich the samples were taken and the penctration resistance valucs arc
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shown on the Logs of Exploratory Borings, Figure 2. The samples were retumed to our
laboratory for review by the project engineer and testing.
SUBSURF'ACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about 6 inches of topsoil overlying medium stiff to stiff, silty sandy clay to
gVzfeet. Medium dense to dense silty sand and gravel underlies the clay to the maximum drilled
depth of l6 feet.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and gradation analyses. Results of swell-consolidation testing performed on relatively
undisturbed drive samples, presented on Figures 4 and 5, indicate low compressibility under
existing moisture conditions and light loading and a low swell or collapse (settlement under
constant load) potential u¡hen wetted. The samples showed a moderate to high compressibility
upon increased loading after wetting. Results of gradation analyses performed on small diameter
drive samples (minus lYz-inch fraction) of the coarse granular subsoils are shown on Figure 6.
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 moist.
FOUNDATION BEARING CONDITIONS
The clay subsoils encountered at the site possess a low bearing capacity and low to moderate
movement potential. The underlying gravel soils possess moderate bearing capacity and a
typicatly low settlement potential. At assumed excavation depths we expect the subgrade will
consist of silty sandy clay soils. Spread footings bearing on the clay subsoils should be feasible
for foundation support of the residence with a risk of movement.
DESIGN RECOMMENDATIONS
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 the natural soils.
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The design and construction criteria presented below should be observed for a spread f'ooting
foundation systenr.
1) Footings placed on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 1,500 psf. Based on experience, we expect
settlement of footings designed and constructed as discussed in this section will
be about I inch.
2\ The footings should have a minimum width of 18 inches for continuous walls and
2 fcct 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 reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 12 feet.
Foundation walls acting as retaining structures should also be designed to resist a
lateral earth pressure coresponding to an equivalent fluid unit weight of at least
55 pcf.
5) All existing fill, topsoil and any loose or disturbed soils should be removed and
the footing bearing level extended down to the relatively dense natural granular
soils. The exposed soils in footing area should then be moistened and compacted.
If water seepage is encountered, the footing areas should be dewatered before
concrete placement.
6) A representative ofthe geotechnical engineer should observe all footing
excavations prior to concrete placement to evah¡ate bearing cclnrlitions,
FLOOR SLABS
Thc natural on-sitc soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-gradc
construction. 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. 'Ihe requirements for joint spacing and slab reinforcement should be established by the
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designer based on experience and the intended slab use. A minimum 4 inch layer of free-
draining gravel should be placed beneath slabs to facilitate drainage. This material should
consist of minus 2-inch aggregatewith at least 50% retained on the No. 4 sieve and less than2Yo
passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site granular 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
the area and where clay soils are present 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, and deep
crawlspace are¿Ìs, be protected from wetting and hydrostatic pressure buildup by an underdrain
system. Shallow crawlspace (less than 3 feet below exterior grade) should not need an
underdrain system provided that good surface drainage is maintained around the residence.
If installed, the drains should consist of drainpipe placed in the bottom of the wall backfill
surrorurded 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 finish grade and
sloped at a minimumTYo to a suitable gravity outlet, such as a drywell. Free-draining granular
material used in the underdrain system should contain less than 2Yopassingthe No. 200 sieve,
less than 50% passing the No. 4 sieve and have a maximum size af 2 inches. The drain gravel
backfill should be at least IYzfeeL deep. An impervious membrane such as 20 mil PVC should
be placed beneath the drain gravel in a trough shape and affached to the foundation wall with
mastic to prevent wetting of the bearing soils.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
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1)lnundation ofthe fbundation excavations and underslab areas should be avoided
during construction.
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.
The ground surface sunounding the exterior of the building should be sloped to
drain away from the foundation in all directions. We recommend a minimum
slope of 6 inches in the first l0 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
capped with filter fabric and about 2 feet of the on-site soils to reduce surface
water infiltration.
Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Landscaping which requires regular heavy inigation should be located at least
5 feet from foundation walls.
2)
3)
4)
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 l, 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 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 rcport has becn prcpared for the exclusive use by our client for dcsign purposcs. Wc arc not
responsible for technical interpretations by others of our infonnation. As the project evolves, we
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should provide continued consultation and field services during construction to review and
monitor the implernentation of our recommendations, and to veriry that the recommendations ,
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recommendations presented herein. W'e 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 & Associafes, Inc.
James H. Parsons, E.I.
Reviewed by:
Daniel E. Hardin,
JHP/kac
cc: Studio M (micbaca(4yahoo.com)
Kumar & AsEociates, lne. o Project No, 19-7-742
APPROXIMATE SCALE-FEET
19-7 -7 42 Kumar & Associates LOCATION OF TXPLORATORY BORINGS Fig. 1
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Fig. 2Kumar & Associates LOGS OF EXPLORATORY BORINGS19-7 -7 42
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LEGEND
TOPSOIb CLAY, SILTY, SANDY, ORGANICS, FIRM, SLIGHTLY MOIST, BROWN.
CLAY (CL); SILTY, SLIGHTLY SANDY TO SANDY, MEDIUM STIFF T0 STIFF, SLIGHTLY MOIST T0
MOIST, RED BROWN,
SAND (SC)¡ GRAVELLY, CLAYEY, SILTY, MEDIUM DENSE TO DENSE, SLIGHTLY MOIST, GRAY
BROWN.
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DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
DRTVE SAMpLE, 1 5/E-|NCH t.D. SpLtT SPOON STANDARD pENETRATION TEST.
15712 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 16 BLOWS OF A 140-POUND HAMMER.-,.- FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER,I2 INCHES.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON JANUARY 6, 2O2O WITH A 4-INCH_DIAMETER
CONTINUOUS-FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY ÏAPING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER
TO BORING 1 AS 1 OO FEET.
4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS 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 (2;) (ASTM D2216);
DD = DRY DENSITY (pcf) (ASTM D2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913);
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM DI140);
19-7 -7 42 Kumar & Associates LEGEND AND NOÏES Fîg. 3
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SAMPLE OF: Sondy Silty Clcy
FROM:Boringl@2.5'
WC = 10.6 %, DD = 107 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
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19-7 -7 42 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 4
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SAMPLE OF: Sondy Silty Cloy
FROM:Boring2@5'
WC = í5.2 %, DD = 90 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WE I IING
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19-7-7 42 Kumar & Associates SWELL-CONSOLIDATION TTST RESULTS Fig.5
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HYDROMEfER ANALYSIS SIEVE ANALYSIS
TIME READINæ
24 hRS 7 HRS
U.S. SIANDARD SERIES CLEAR SOUARE OPENINCS
nf
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90
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60
50
40
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70
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DIAMETER OF PARTICLES IN MILLIMETERS
152
CLÂY TO SILT COBBLES
GRAVEL 31 % SAND
LIQUID LIMIT
SAMPLE OF: Sllly Grovelly Sond
49%
PLASTICITY INDEX
SILT AND CIAY 20 %
FROMrBorlngl@10'&15
Th€se losl rorulls dpply only to th€
sompl€s which w€a€ lssl€d. Th€
loellng r€port sholl.oi b6 r€produced,
oxc.pl ln tull, wllhoul lh. wr¡tlon
approvol ol Kumor & Assoclqlrs, lnc.
Sl.vr onolysts lèsllng ls porto.ñod ln
occordoncê vllh ASTM D6913, ASÍM 07928,
ASÍM C156 ond/or ASTM Dff4O.
SAND GRAVEL
MEDIUM ICOARSE FINE COARSEFINE
19-7 -7 42 Kumar & Associates GRADATION TEST RESULTS Fig. 6
l(;rÂiffilffiiffi*i'iii'*"TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.19-7-742Silty Gravelly SandSandy Silty ClaySOIL TYPESandy Silty ClaySilty ClayfpsñUNCONFINEDCOIüPRESSIVESTRENGTH{ryolPLASNCINDEXATIERBERG LITITSlo/o\LISUID LIfÍITPERCENTPASSING NO.200 stEvE9420twSAND49GRADAÌIONi"/ùGRAVELI390NATURALDRYDENCTY(ocf)ra710.693l9'o)NATURALITOISTURËCONTEIIT12.8-tL15.2(fr)DEPTHzrt510&155SAIIPLE LOCATIONBORING12