HomeMy WebLinkAboutSubsoil Studyt(+rtiiffifimfmF.""
An Employcc Owncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumaru$a,com
www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Spríngs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR TOUNN¡TION DESIGN
ÈnoposnD RESTDENCElor r,'coRYELL RANCH
STONEF'LY NNTVN
GARFIELD COUNTY, COLORADO
PROJECT NO.2l-7-492
JULY 19,2021
PREPARED FOR:
PEAK 3 STONEFLY LLC
C/O PEAK 3 CONSTRUCTION + DEVELOPMENT
ATTN: BRYANT RAGAN
601 EAST HOPKINS AVENUE, SUITE 202
ASPEN, COLOR.A.DO 81611
brvant@.oeak3 asnen.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS
SIIBSIDENCE POTENTIAL.
FIELD EXPLORATION
SUBSURFACE CONDITIONS
DESIGN RECOMMENDATIONS ..
FOLTNDATIONS
FLOOR SLABS
UNDERDRAIN SYSTEM....
SURFACE DRAINAGE.
LIMITATIONS
FIGURE 1 . LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - GRADATION TEST RESULTS
TABLE 1 _ SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Associates, lnc. @ Project No.2l-7-492
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PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot 1,
Coryell Ranch, Stonefly Drive, Garfield County, Colorado. The project site is shown on Figure
1. The purpose of the study was to develop recoÍìmendations for the foundation design. The
study was conducted in accordance with our agreement for geotechnical engineering services to
Peak 3 Stonefly, LLC dated }lday 26,2021.
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 andlaboratory 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
The proposed residence will consist of a single-story wood-framed structure with attached garage
and a detached barn and ADU. Ground floors will be structural floor over crawlspace in the
residence and slabs-on-grade for the garage and barn. Grading for the structure is assumed to be
relatively minor with cut depths between about 3 to 6 feet. 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 lot was vacant of structures at the time of our visit. Vegetation consists of grass and weeds,
and the ground surface is relatively flat with a slight slope down to the east and southeast.
Elevation difference across the buildin g area is about 2 feet. The lot is bordered on the northeast
by the Roaring Fork River, and on the south by Stonefly Drive.
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SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies the lower Coryell Ranch
Subdivision. These rocks af,e a sequence of gypsiferious shale, fine-grained sandstone/siltstone
and limestone with some massive beds of gypsum. There is a possibility that massive gypsum
deposits associated with the Eagle Valley Evaporite underlie portions of the property.
Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can
produce areas of localized subsidence. During previous work in the area, several broad
subsidence areas and sinkholes have been observed. These sinkholes appear similar to others
associated with the Eagle Valley Evaporite in areas of the lower Roaring Fork River valley.
No evidence of subsidence or sinkholes were observed on the property or encountered in the
subsurface materials, however, the exploratory borings were relatively shallow, for foundation
design only. Based on our present knowledge of the subsurface conditions at the site, it can not
be said for certain that sinkholes will not develop. The risk of future ground subsidence atthe
site throughout the service life of the structure, in our opinion is low, however the owner should
be 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 lune 21,2021. Three 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 and
Associates.
Samples of the subsoils were taken with a l3/a 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 aî indication of the relative density or consistency of the
subsoils. Depths at which the samples v/ere 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.
Kumar & Associates, lnc. ô Project No.21-7-492
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SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. In
Borings 1 and 3, the subsoils below about 6 inches of topsoil consist of slightly silty to silty
sandy gravel with cobbles and probable small boulders down to the maximum depth explored,
8 feet. In Boring 2, the subsoils below about 6 inches of topsoil consist of slightly siþ to silty
sandy gravel with cobbles and probable small boulders with interbedded layers of silty sand
down to the maximum depth drilled of 9 feet. Drilling in the dense granular soils with auger
equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in
all three borings in the deposit.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and gradation analyses. Results of gradation analyses performed on small diameter drive
samples (minus lVz-inch fraction) of the coarse granular subsoils are shown on Figure 3. The
laboratory testing is summarizedin Table 1
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
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 granular soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 3,000 psf. Based on experience, we expect
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less.
2) The footings should have a minimum width of 16 inches for continuous walls and
2 feet for isolated pads.
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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.
Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 10 feet.
Foundation walls acting as retaining structures should also be designed to resist a
lateral earth pressure coffesponding to an equivalent fluid unit weight of at least
45 pcf for the onsite sand and gravel soil as backfill.
All 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.
A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
4)
FLOOR SLABS
The natural on-site granular soils, exclusive of topsoil, are suitable to support lightly loaded slab-
on-grade 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. 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 well graded
sand and gravel (such as road base) should be placed beneath slabs for support. This material
should consist of minus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less
than 12o/o passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95o/o 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
It has been our experience in the arcathat local perched groundwater can develop during times of
heavy precipitation or seasonal runoff. Frozen ground during spring runoff can øeate a perched
5)
6)
Kumar & Associates, lnc, o Project No.21-7-492
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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 and
wall drain 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
excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum 1o/oto
a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain
system should contain less than 2%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 I%feet
deep.
SIIRFACE DRAINAGE
The following drainage precautions should be observed 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
during construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95o/o of the maximum standard Proctor density in pavement and slab areas
and to at least 90/o 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 6 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 backfrll should be
covered with filter fabric and capped with about 2 feet of the on-site finer graded
soils to reduce surface water infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
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.
Kumar & Associates, lnc. o Project No. 21-7-492
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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 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 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 continued 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 recoÍlmendations 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,
I(umar & Associates, Inc.
David A. Noteboom, Staff Engineer
Reviewed by:
Steven L. Pawlak, P.
SLPlkac
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Kumar & Associates, lnc, @ Project No.21-7-492
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BORING 1o
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APPROXIMATE SCALE_FEEÏ
21 -7 - 492 Kumar & Associates LOCATION OF TXPLORATORY BORINGS Fig. 1
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+4=47
-2Q0=1 4
BORING 1
EL. 6082'
BORING 2
EL. 6082.5'
BORING 3
EL. 6081.5'
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TOPSOIL; SANDY TO VERY SANDY CLAY, SOME GRAVEL, ROOTS AND ORGANICS, FIRM'
SLIGHTLY MOIST, LIGHT BROWN.
GRAVEL AND SAND (GM-SM); COBBLES PROBABLE SMALL BOULDERS, SLIGHTLY SILTY TO
SILTY, VERY DENSE, SLIGHTLY MOIST, LIGHT GRAY TO GRAY AND TAN. ROUNDED ROCK
GRAVEL AND SAND (GP-SM); COBBLES PROBABLE SMALL BOULDERS, SLIGHTLY SILTY TO SILTY,
WITH LAYERS OF SILTY SAND, VERY DENSE, SLIGHTLY MOIST, REDDISH TAN TO TAN. ROUNDED
ROCK.
i DRTVE SAMPLE, 1 3/8-|NCH l.D. SPLIT SPOON STANDARD PENETRATION TEST
82/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 82 BLOWS OF A 14o_POUND HAMMER
FALLING 50 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
I PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON JUNE 21 , 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 THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURAÏE
ONLY TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE 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 ÏHE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ISTU OOSIS);
_2OQ= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM 01140).
WC=1.1
+4=39
-200=8
21 -7 -492 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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SIEVE ANALYSISHYDROMETER ANALYSIS
U.S. STANDARO SERIES CLEAR SQUARE OPENINGS
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DIAMETER OF PA INM
CLAY TO SILT COBBLES
GRAVEL 47 % SAND
LIQUID LIMIT
SAMPLE OF: Silty Sond ond Grovel
39%
PLASTICITY INDEX
SILT AND CLAY 14 %
FROM: Borlng 1 O 2.5' & 5' (Gombined)
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,425R OF PARTICLES IN MI
152
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CLAY TO SILÏ COBBLES
GRAVEL 39 % SAND 53
LIQUID LIMIT
SAMPLE OF: Slightly Silty Sond ond Grovel
%
PLASTICITY INDEX
SILT AND CLAY 8%
Thcse l6sl rêsulls opply only to lh€
somples whlch wrrc t€st€d, th.
icallng report sholl nol bo roproducsd,
óxcepl in full, wllhoul lh6 written
opprovol of Kumqr & Assoc¡otss, lnc,
Slôvê dnolysls lostlng ls pcrformcd ln
occordonco wlth ASÍM 06913, ASIM 07928,
ASTM C136 ond/or ASTTJ Dl1,{0.
FROM: Boring 2 O 5' & 7.5' (Combined)
SAND GRAVEL
FINE COARSEFINEMEDIUMCOARSE
SIEVE ANALYSISHYDROMETER ANALYSIS
CLEAR SOUARE OPEflINGS
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fIME REAOINOS sÊRtEs
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COARSEFINEMEDTUM ICOARSE FIN E
21-7 -492 Kumar & Associates GRADATION TEST RESULTS Fig. 3
l(+rtH,Ë*fi'ffiffint':iü'*"TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.2l-7-492SAMPLENATURALMOISTURECONTENTNATURALDRYDENSITYUNCONFINEDCOMPRESSIVESTRENGTHGRAVELSANDPERCENTPASSING NO.200 stEvEPLASTICINDEXPITDEPTHLIQUID LIMITSOIL TYPE(/"1(%)12/z and 5combined1.14739T4Silty Sand and Gravel25 andT%combined1.139538Slightly Siþ Sand andGravel