HomeMy WebLinkAboutSubsoils Study for Foundation DesignI Crt i;iËilå#ffÉtrnr'riå'*"5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www. kumarusa. com¿in Employca 0v¡ncd Compqny
Office Locations: Denver (HQ), Parkeq Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
October 26,2022
Resort Development Building
Attn: Chance Soldoff
99 Elfin Place
Glenwood Springs, Colorado 81601
soldoff5@aol.com
Project No.22-7-699
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 56, Filing 9,
Elk Springs,3l7l Elk Springs Drive, Garfield County, Colorado
Dear Mr. Soldoff:
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 October 20,2022. 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. The lower floor may be slab-on-grade or structural over crawlspace, located on the site
as shown on Figure 1. Cut depths are expected to range between about 3 to 8 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 site was vacant at the time of our site visit. Vegetation consists of pinon
and juniper trees with an understory of sparce grass and weeds. The lot slopes down to the south
at about 10 to l5 percent. The driveway and building area had been cleared of trees and topsoil.
Basalt rocks and small boulders were exposed in the cleared portion of the site.
Subsurface Conditions: The subsurface conditions at the site were evaluated by observing
three previously excavated pits at the approximate locations shown on Figure 1. The logs of the
pits are presented on Figure 2. The subsoils encountered, below about % to 1 foot of topsoil,
consist of basalt rocks in a calcareous sandy silt matrix. A one-foot-thick layer of stiff, sandy
silty clay was encountered overlying the basalt rocks in Pit 3. No free water was observed in the
pits at the time of our site visit and the soils were slightly moist.
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Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread fo
placed on the undisturbed natural soil designed for an allowable bearing pressure for
support of the proposed residence. Footings should be a rninimum width of l6 inches
continuous walls and 2 feet for columns. Loose and disturbed soil and existing clay and topsoil
cttcoutrtctcd at thc fuuntlatiurr bcaring level wilhin the excavation slruulcl be rerrruvetl und l.he
footing bearing level extended down to the undisturbed natural basalt rock soils. We should
observe the completed excavation for bearing conditions. Exterior footings should be provided
with adequate cover above their bearing elevations for frost protection. Placement of footings at
least 36 inches helow the exterior gracle is typically usecl in this area. Continuous founclation
walls should be reinforced top and bottom to span local anomalies such as by assuming an
unsupported length of at least l0 feet. Foundation walls acting as retaining structures should be
designed to resist alateral earth pressure based on an equivalent fluid unit weight of at least
50 pcf forthe on-site soilas backfillexcluding organics and rock largerthan 6 inches.
Floor Slabs: The natural on-site 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 allbearing 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 basement level slabs to facilitate drainage.
This material should consist of minus 2-inch aggregate with less than 50Yo passing the No. 4
sieve and less than 2Yo passing the No. 200 sieve.
All filI 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 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 that local perched groundwater can develop during times of
heavy precipitation or seasonal runoff. Frozen ground during spring runoffcan create a perched
condition, Wç rçcommend 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
thc invcrt lcvcl with frcc-draining granular matcrial. Thc drain should bc placcd at cach lcvel of
2,000
Kumar & Associates, lnc. o Project No, 22-7-699
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excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum lYoto
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2Yo 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.
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 capped with about 2 feet of the on-site, finer
graded soils to reduce surface water infiltration.
3) The ground surface surounding 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 l0 feet in unpaved areas and a minimum slope of
3 inches in the first l0 feet in pavement and walkway areas. A swale will be
needed uphill to direct surface runoffaround the residence.
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. The conclusions and recommendations submitted in this report are based
upon the data obtained from the exploratory pits excavated at the locations indicated on Figure I
and to the depths shown on Figure 2, 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 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 made.
Kumar & Associates, lnc, o Project No. 22-7-699
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This report has been prepared for the exclusive use by our client for design purposes. We are not
responsiblc fcrr technical interpletations by others of uu'irfoun¿tiou. As the project evolves, we
should provide continued consultation and field services during construction to review and
monitor the implcmentation of our recommendations, and to verifr that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
r:r'modifications to the recrurmenúal.iuns presenl,ed herein. 'We re!:uuuuend un-site obscrvatiorr
of excavations and foundation bearing strata and testing of structural fill by 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,Inc.
Daniel E. Hardin, P
Rev. by: SLP
DEH/kac
attachments Figure I - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
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Kumar & Associates, lnc. 6r Project No. 22.7.699
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BOUNDARY AND TOPOGRAP
LOT 56, FILING 9, LOS AMIGOS RANCH
COUNTY OF GARFI ELD, STATT OF COLORAT
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APPROXIMATE SCALE-FEET
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PIT 1
22-7 -699 Kumar & Associates LOCATION OF TXPLORATORY PITS Fig. 1
PIT 1
EL. 986'
Pfi2
EL. 987'
PIT 3
EL. 987'
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LEGEND
ToPSOIL: ORGANIC SANDY SILT, SOFT, SLIGHTLY MOIST, DARK BROWN
CLAY (cL): SILTY, SANDY, ST¡FF, SLIGHTLY MolST, LIcHT BROWN
BASALT ROCKS (cM-cp) tN sANDy stLT MATR|X, MEDTUM ,DENSE TO DENSE,
SLIGHTLY MOIST, WHITISH MATRIX SOILS.
I PRACTICAL REFUSAL ON BOULDERS.
NOTES
THE EXPLORATORY PITS HAD BEEN EXCAVATED WITH A BACKHOE PRIOR TO OUR SITE VISIT ON
ocToBER 20, 2022.
2. THE LOCATIONS OF THE EXPLORATORY P¡TS 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 BTTWEEN MATERIALS SHOWN ON THE EXPLÔRATORY 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 OBSERVATION
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22-7 -699 Kumar & Associates LOGS OF EXPLORATORY PITS Fi1. 2
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