HomeMy WebLinkAboutS.E.O.R Report ReceivedIC fliffilfi'ff:Tf#fn$r'i'*"
An Employcc Owncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
August 31,2021
Jordan Architecture
Attn: Brad Jordan
P.O. Box 1031
Glenwood Springs, Colorado 81602
bradj ordan architect@ gmai l. com
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Subject: Subsoil Study for Foundation Design,Residence, Lot 31, Filing 5,
Los Amigos Ranch, Elk Springs Drive, Garfield County, Colorado
Gentlemen:
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 Jordan Architecture dated July 14,2021. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: Plans for the proposed residence were conceptual at the time of our \
study. The residence will generally be a one- or two-story wood-framed structure over a walkout -.S
basement level with attached garage located within the building envelope shown on Figure l. N
Ground floors could be a combination of structural over crawlspace and slab-on-grade with cut ^Sdepths between about 2 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 diflerent 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. The ground
surface is sloping down to the south at a grade of about 10 percent. The lot is forested with
juniper trees and an understory of grass. Basalt boulders were visible on the ground surface.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
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 I foot oftopsoil, consist of dense,
sandy basalt gravel and cobbles with boulders in a calcareous sandy silt matrix. Results of a
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gradation analysis performed on a sample of silty very sandy gravel (minus 3-inch fraction)
obtained from the site are presented on Figure 3. No free water was observed in the pits at the
time of excavation and the soils were slightly 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 thg undisturbed natural soil designed for an allowable bearing pressure of 2,500 psf
for support of the proposed residence. The matrix soils tend to compress after wetting and there
could be some post-construction foundation settlement. Footings should be a minimum width of
l6 inches for continuous walls and 2 feet for columns. 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 granular 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 lengfh of at least 12 feet. Foundation walls acting as retaining
structures should be designed to resist a lateral earth pressure based on an equivalent fluici unit
weight of at least 45 pcf for the on-site soil as backfill excluding organics and rock larger than
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 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 basement level slabs to facilitate drainage.
This material should consist of minus 2-inch aggregate with less thsn 50% passing the No. 4
sieve and less than 2Yo passingthe No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least95%o of maximum
standarci Proctor ciensity at a moisture content near optimum. Requireci fiii 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 runoff can create a perched
Kumar & Associates, lnc. o Project No. 21-7-608
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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
system.
The drains should consist of drainpipe placed in the bottom ofthe 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 lo/o to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2o/opassingthe No. 200 sieve, less than 50ol passing the No. 4 sieive and-have a
maximum size of 2inches. The drain gravel backfill'should bd at.least l/'feetdeep.
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% 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 covered with filter fabric and capped with
about 2 feetof 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 l0 feet in unpaved areas and a minimum slope of
3 inches in the first l0 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
5 feet from the building. Consideration should be given to the use of xeriscape to
limit potential weffing of soils below the foundation caused by irigation.
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
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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 reporto we should be notified at once so 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 verifu 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 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.
James H. Pmsons,
Reviewed by:
fb';/.
Steven L. Pawlak, P.E.
JHPlkac
attachments Figure I - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Gradation Test Resuits
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21 -7 -608 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
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PIT 1
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PIT 2
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LEGEND
TOPSOIK SILT AND CLAY, SANDY, ORGANICS, SOFT, SLIGHTLY MOIST, BROWN
GRAVEL
DENSE,
(CC-OU); BASALT COBBLES, BOULDERS, SANDY SILT HIGHLY CALCAREOUS MATRIX,
SLIGHTLY MOIST, LIGHT TAN AND GRAY.
DISTURBED BULK SAMPLE.
t PRACTICAL DIGGING REFUSAL.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON AUGUST 6, 2021.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
5. 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 MATERIAL5 SHOWN UN THE EXPLORATORY PlT 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. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORA.TORY TEST RESLILTS:+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
-2OO= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
21 -7 -608 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
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HYDROYET€R ANALYSIS SIEVE ANALYSIS
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PARTICLES IN MILLIMETERS
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DIAMETER OF
CLAY TO SILT COBBLES
GRAVEL 19 % SAND
LIQUID UMIT
SAIIPLE OF: Sltty Very Sondy Grovel
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PLASTICITY INDEX
SILT AND CLAY 13 %
FROM:Pit2O3'-1'
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occo.donc! rilh ASTM D6913, ASTI, D7924,
ASTY ct36 qndlor ASIY Dll,lo.
SAND GRAVEL
FINE MEOIUM lCOanSE FINE COARSE
21 -7 -608 Kumar & Associates GRADATION TEST RESULTS Fig. 3