HomeMy WebLinkAboutSubsoil StudyI n'rt ii"eïå:i:**'l'Ë; ; *' ^
An Employso Owned Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970)945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.corlt
Offrce Locations: Denver (HQ), Parker', Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
RECEIVED
February 22,202I
Robert Dunn
2648 County View Court
Berthod, Colorado 80513
bskiing@.msn.com
0cT fJ 6 2021
GARFIELD COUNTY
COMMUNIW DEVELOPMENT
Subject:
Project No. 21-7-141
Subsoil Study for Foundation Design, Proposed Residence, LoIJï, Filing 7,Elk
Springs, 1675 Elk Springs Drive, Garfield Country, Colorado
Dear Robert:
As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations at
the subject site. The study was conducted in accordance with our agreement for geotechnical
engineering services to you dated January 19,2021. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: The proposed residence will be a one and two story wood frame
structure with attached garage located on the site as approximately shown on Figure 1. Ground
floors will be a combination of structural over crawlspace and slab-on-grade. Cut depths are
expected to range between about 2 to 7 feet. Foundation loadings for this type of construction
are assumed to be relatively light and typical of the proposed type of construction.
If building conditions or foundation loadings are significantly different from those described
above, we should be notified to re-evaluate the recommendations presented in this report.
Site Conditions: The subject site was vacant at the time of our field exploration with
approximately 6 to 12 inches of snow cover. The ground surface is gently sloping down to the
west in the buildin g area getting steeper to the west. Vegetation consists of sagebrush, grass and
weeds. Pinyon pines are growing to the west of the proposed building area.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
3 exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about lz foot of topsoil, consist of I to
2 feet of very stiff sandy clay underlain by dense basalt gravel, cobbles and boulders in a highly
calcareous (caliche) silt matrix to the maximum pit depth of 5 feet. Digging in the dense cobbles
and boulders was difficult and excavation refusal was encountered in the pits. Results of swell-
a
consolidation testiltg perlofined on a relatively undisturbed sample of the sandy clay, presented
orr Figure 3, indicate minor compressibility under existing moisture conditions and light loading
aud a low expansion pol"cnLi¿l when weLtetl. No free water was observed in the pits at the time of
exoavation and the soils were slightly moist to moist.
Foundation Recommendations: Considering the subsoìl conditions encountered in the
exploratory pits and the nature of the proposcd construction, we recommend spread footings
placed on the undisturbed natural soil designed for an allowable bearing pressure of 1,500 psf for
supporl of the proposed residence. There is a risk of foundation movement of around 1 to
2 inches possibly resulting in distress if the bearing soils become wetted. Placing the spread
footings on the underlying dense gravel soils would reduce the risk of foundation movement.
Footings placed entirely on the underlying dense gravel soils can be designed for an allowable
bearing pressure of 2,500 psf. Footings should be a minimum width of 16 inches for continuous
walls and 2 feet for columns. The topsoil and loose disturbed soils encountered at the foundation
bearing level within the excavation should be removed and the footing bearing level extended
down to the undisturbed natural soils. Exterior footings should be provided with adequate cover
above their bearing eleval.iorts fur frost protection. Placement of footings at least 36 inches
below the 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 72 feet. Foundation walls acting as retaining structures should be designed to resist a
lateral earth pressure based on an equivalent fluid unit weiglrt of at least 50 pcf for the orr-site
soil as backfill. A sliding coefficient of 0.40 and equivalent fluid lateralpassive earth pressure of
375 pcf can be used to resist lateral loading on the foundation.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded
slab-on-grade construction. To reduue Lhe elfeots of sorne tlillerenLial rnovement, 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 slrrirrkage 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 to facilitate drainage.
This material should consist of minus 2-inch aggregate with less than 50o/o passing the No. 4
sieve and less than 2o/o passing the No. 200 sieve.
All fill materials for support of tloor slabs should be compacted to at least 95Yo of maximum
standard Proctor density at a moisture content near optimum. Required filI can consist of the on-
site soils devoid of vegetation, topsoil ancl oversized rock or imported gravel such as road base.
Kumar & Associates, lnc. @ Project No. 2l-7-14'l
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Underdrain System: Although free water was not encountered during our exploration, it has
been our experience in the areaÍhat 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 (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 surrounded above
the invert level with free-draining granular material. The drain should be placed at each level of
excavation and aI least 1 foot below lowest adjacent finish grade and sloped at a minimum lYoIo
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2o/, passingthe 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.
Surface Drainage: 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. Drying could increase the expansion potential of the clay
soils.
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 90o/o of the maximum standard Proctor density in landscape areas.
Free-draining wall backfill should be covered with filter fabric and capped with
about 2 feet of the on-site, finer graded soils to reduce surface water infiltration.
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 i0 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in pavement and walkway areas.
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
l0 feet from the building. Consideration should be given to the use of xeriscape
to limit potential wetting of soils below the foundation caused by irrigation.
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 trom the exploratory pits excavated at the locations indicated on Figure I
Kumar & Associates, lnc. 6 Project No. 21-7-141
-4-
and to the depths shown on Figure 2,theproposed type of construction, and our experience in
the area. Our services do not include determining the presence, prevelrtion or possibility of mold
or othcrbiological contaminants (MOBC) doreloping 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 pits 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 at once so re-evaluation of the
recommendations may be macle.
This report has been preþared 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 recommendations presented herein. We recommend on-site observation
of excavations and foundation bearing strata and testing of structural filIby a representative of
the geotechnical engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
Kumar & Associates, fnc.
James H. Parsons, E.I.
Reviewed by:
Steven L. Pawl
JHPlkac
affachments
oo:
Exploratory Pits
Figure 2 -of Exploratory Pits
Figure 3 * Swell-Consolidation Test Results
Table I - Summary of Laboratory Test Results
Patrick Stuckey - stucarch@comcast.neti
152n
Kumar & Assocíates, lnc. @ Project No. 21.7.141
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FN
2 0 25 50
APPROXIMATE SCALE-FEET
21 -7 -1 41 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
a: 't/
/F
PIT I
EL. 979.5'
Pl'l 2
EL. 978'
PIT 3
EL. 975'
0 0
t--t¡lt¡l
LL
I-F-fL
t¡Jtl
WC=7.8
DD=03
I
J
t-tiJ
LrlL!
ITt'-o-
UJô
5
WC=13.9
DD=89 5
LEGEND
TOPSOIL; SILT AND CLAY, SANDY, ORGANICS, FIRM, SLIGHTLY MOIST, DARK BROWN.
cLnY (ct-); stLTY, SANDY, VERY STtFF, SLtcHTLY MO|ST, BROWN, BLOCKy, MEDTUM
PLASTICITY.
GRAVEL (OV_VH); BASALT COBBLES AND BOULDERS, SANDY SILT MATRIX (CALICHE),
DENSE/VERY STIFF, SLIGHTLY MOIST, PALE TAN.
F
Ii
I
HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE
DISTURBED BULK SAMPLE.
PRACTICAL DIGGING REFUSAL.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON FEBRUARY 2,2021.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN
^^\tT^t tñê ^\t tt tF êtrFuur\ r uuf\J \.,l\ I nÊ Jt I Ê TLAt\ rt\\JvtuÈ.u.
4. THE EXPLORATORY PIT 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 PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (PCI) (ASTU D 2216).
21 -7 -1 41 Kumar & Associates LOGS OF TXPLORATORY PITS Fig. 2
SAMPLE OF: Sondy Cloy
FROM: Pit 1 @ 1'
WC = 7.8 %, DD = 93 pcf
(
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
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APPLIED PRESSURE - KSF 10 t00
21 -7 -1 41 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.21-7-141
GRADATION ATTERBERG LIMITSNATURAL
DRY
Pit DEPTH DENSIry
NATURAL
MOISTURE
CONTENT
GRAVEL
u"t
SAND
(%l
PERCENT
PASSING NO.
200 sIEVE
LIQUID LIMIT
lot tol^t
PLASTIC
INDEX
lhsl'l
UNCONFINED
COMPRESSIVE
STRENGTH SOIL TYPE
1 I 7.8 93 Sandy Clay
2 4 13.9 89 Sandy Silt (Caliche)