HomeMy WebLinkAboutSubsoil Studyrc,l*ffiil#í#ß:?"Hl*Ë;å**
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An Employm Owntd GomÞony
5020 €ounty Road 154
Glenu'osd Sptings, €O El60l
phone: (9?0) 945"7988
faxr (970) q45^8454
emai I : kaglenwoodq@kumarusa,eont
wtuil,kumÂrusg,€am
Subject
OfrlEe L,osations; Denver.(t{Q), Parker.. €olorado Springs, Fort eollins, Glenrvood Springs, attd Sunirnit eounç eolorado
December 14,2020
Travis Schultz
300 Wulfsohn Road, Apt. #D309
Glenwood Springs, Colorado 81601
timin gthatsal I@nte.eom
Project No.20-7-644
Subsoil Study for Foundation Design, Proposed Residence, 180 Aster Drive, Lot
64, Filing 7, Elk Springs, Garfield County, Colorado
Dear Travis:
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 Octob er 26,2020. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: Design plans have not been developed. The proposed residence will
be one to two stories of wood frame construction over a crawlspace or walkout basement. The
basement and attached garage floors will be slab-on-grade. The house will be in the area of the
pits on the site shown on Figure 1. Cut depths are expected to range between about 4 to l0 feet.
Foundation loadings for this type of construction are assumed to be relatively light and typical of
the proposed type ofconstruction.
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 site is vacant and vegetated with sagebrush and grass. The topography of
the building area is moderately steep sloping down to the southeast at a grade of about 25Vo. T}:re
upper part of the site, above the building area, is near the top of a broad, southwest-trending
ridge which slopes down to the southwest at about l\Vo grade. The lot to the east is developed
with a single family home.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
three exploratory pits at the approximate locations shown on Figure l. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about 6 to l0 inches of topsoil, consist
1
of 2 to 4 feet of very stiff to hard, brown, sandy silty clay overlying hard, white sandy silt with
basalt gravel and cobbles. Results of swell-consolidation testing performed on a relatively
undisturbed sample ofthe brown, stiff clay from Pit l, presented on Figure 3, indicate low
compressibility under existing moisture conditions and light loading and a low to moderate
expansion potential when wetted. No free water was observed in the pits at the time of
excavation and the soils were slightly moist to moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
placed on the undisturbed natural silty soils with basalt rocks, below the upper brown clay soils,
designed for an allowable soil bearing pressure of 3,000 psf for support of the proposed
residence. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for
columns. Loose disturbed soils and brown clay encountered at the foundation bearing level
within the excavation should be removed and the footing bearing level extended down to the
undisturbed natural rocky soils. Exterior footings should be provided with adequate cover above
their bearing elevations for 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
12 feet. Foundation walls acting as retaining structures should be designed to resist alatetal
earth pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil as
backfill.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded
slab-on-grade construction. In the brown clay areas, we recommend that at least 2 feet of the
clay be removed from below slab areas. Slab subgrade can be re-established with imported
t/o-inchroad base sandy gravel. 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 interior slabs to facilitate drainage. This
material should consist of minus 2-inchaggregate with less than 50Yo passing the No. 4 sieve and
less than 2Vo 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 should consist of
imported t/o-inchroad base devoid of vegetation, topsoil and oversized rock'
Kumar & Associates, lnc. o Project No. 2È7-641-
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Underdrain System: Although free water was 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 runoff can also create a
perched 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 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 I foot below lowest adjacent finish grade and sloped at a minimum l%oto
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2%ó passingthe 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 lYz feet deep.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the residence has been completed:
l) Inundation of the foundation excavations and underslab areas should be avoided
during construction. Drying could increase the expansion potential of the brown
clay soils.
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 90Yo of the maximum standard Proctor density in landscape areas.
Free-draining wall backfill should be 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 10 feet in unpaved areas and a minimum slope of 3
inches in the first l0 feet in pavement and walkway areas. A swale may be
needed uphill to direct surface runoffaround the residence.
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 ofxeriscape 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
Kumar & Associates, lnc. o Project No. 2È7-64/
4
øçr€8r orlmplled. Ttc eonelu¡lon¡ and reeommqtâatlanasubmitt€d ln thi¡ repafrarebæed
uponth€ dataabtalned ftom &cexploraØry pits cxeavated at the loaations indioated on Figure 1
and to the dqtho ehown on Figure Z,thcproposed t¡rye of oonstruetion, and our oxpdenec in
thc a¡ca ûlr cüyi€€s do not inalude d*mintng the preræeo rgetætlanor poseibllþ of mold
or othsbiologiaal contaminante (MOBQ develqing in the ftrtue. Ifthe eliøtis eonoffi€d
about MOBC, thcn'a professional in tlriE cpecial field of pactiso Ehould be e.onsult€d. Our
findings include intqolation and exAepolation of the subcwfsc,€ eonditions identificd at the
expløatory pits and variatisns in the subsurfaee csnditisns may not become widøt until
qrsavation is p€rfsrn€d, If conditions €neountffed duríug oonsh¡€ûion appear difføent from
those desqibed in this report, wc shouldbe notified at onc€ co tt-waluation of the
rccomnendatisns may be made.
This report has beør prepryed for the exclusive us€ by orn client for deign purposes. We ue not
ryonrible for technical interpretations by otbers of ow information, As the plojeo{ wolves, we
shouldprovide oontinued consultation and field sør¡ioee during consbustion to rcview and
monitor the implemørtation of orn reæmmendations, and to veriS that the r€oomm€ndations
have bocn apprropriately interpreted. Sigrdficant design changes may require additional analysis
or modifcations to the reconm€ndations presented h€ûein- We recomrnemd on-siæ obserrntion
of excavations and foundation bearing sEata and testing of structr¡ral fill by a rtpreseirtative of
the geotecbnical engineer.
If you have any questions or if we may be of further assistmce, please let us know.
Respectñ¡lly Sr¡bmitte{
Kumar & Associates.
Daniel E. Hadin, P
Reviewdby:
Steven L. Pawlak, P.E.
DEHlkac
attachments Fig¡¡re t - Location of Exploratory Pits
Figt¡re 2 - Loæ of ÞcPloratorY Pis
Figì¡¡e 3 - Swell-Conwlidation Test Resuls
Kumar & Associates, lnc.6 Project No. 2A:l-6M
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TO ASTER DRIVE
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ELEV=6870.80'
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20
PIT 1
APPROXIMATE SCALE-FEET
Fig.LOCATION OF EXPLORATORY PITSKumar & Associates20-7 -644
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PIT 1
EL. 6890'
Ptl 2
EL. 6886'
PIT 3
EL. 6886'
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WC=8.6
DD=1 1 1
55
TOpSO|L; ORGAN|C StLTy SAND AND CLAY WITH ROOTS, SOFT TO MEDIUM STIFF, SLIGHTLY
MOIST TO MOIST, DARK BROWN.
CLAY (CL); SANDY, SILTY, VERY STIFF TO HARD, BROWN, SLIGI{TLY CALCAREOUS.
stLT (ML-MH); SANOV, W|TH SCATTERED BASALT ROCKS FROM GRAVEL TO COBBLE SIZE,
HARD, SLIGHTLY MOIST, WHITE, CALCAREOUS.
HAND DRIVE 2-INCH DIAMETER LINER SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON NOVEMBER 4, 2O2O.
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
CONTOURS ON THE SITE PLAN PROVIDED.
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 (PCf) (ASTM D 2216);
F
Fi1. 2LOGS OF EXPLORATORY PITS20-7 -644 Kumar & Associates
SAMPLE OF: Sondy Silty Cloy
FROM:Pit1¡g^2'
WC = 8.6 %, DD = 111 pcf
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20-7 -644 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3
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