HomeMy WebLinkAboutSubsoils Report for Foundation DesignI l,' f I andEnvironmentalscientists
An Employos Ownod Compony
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
November 13,2024
Ted Vickerman
P.O. Box 342
Avon, Colorado 81620
tedvic@comcast.net Project No.24-7-559
Subject:Subsoil Study for Foundation Design, Proposed Accessory Dwelling Unit (ADU)
and Garage, Parcel No. 186323200099, Near 995 Sweetwater Road, Garfield
County, Colorado
Dear Ted:
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 September 19,2024. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered
are presented in this report.
Proposed Construction: The proposed ADU and garage will be two-story wood-frame
structure with a footprint of approximately 1,200 square feet located on the site as shown on
Figure 1. The structure will consist of a garage on the lower level with the ADU above the
garage. Ground floor will be slab-on-grade. Cut depths are expected to range between about
2 to 5 feet. Foundation loadings for this type of construction are assumed to be relatively light
and typical of the proposed type of con0struction.
If building conditions or foundation loadings are significantly different from those described
above, we should be notified to re-evaluate the recofilmendations presented in this report.
Site Conditions: The subject site was avacantpasture and hay field at the time of our field
exploration. The ground surface was gently to moderately sloping down to the south grade of
between 5 and 10 percent. There were basalt boulders and cobbles visible on the surface of the
site. VegetatiOn'crumtSfs of grass, bushes and scattered stands of cottonwood trees.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating one
exploratory pit and two profile pits at the approximate locations shown on Figure 1. The logs of
the pits are presented on Figure 2. The subsoils encountered, below about I to l% feet of topsoil,
consist of medium dense to dense, silty sandy gravel and cobbles to the maximum explored
depth of 9 feet. Results of a gradation analysis performed on a sample of silty sandy gravel
(minus 5-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 and profile pits and the nature of the proposed construction, we recommend spread
footings placed on the undisturbed natural soil designed for an allowable soil bearing pressure
olp;uartsupport of the proposed ADU and garage. Footings should be a minimum width
of t6 inches for continuous walls and2 feet for columns. Loose, disturbed soils and existing fill
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 elevations for frost protection. Placement
of footings at least 36 inches below the exterior grade is typically used in this area. Continuous
foundation walls\6'ffi6'bftn 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 alateral 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. 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 than 50% passing the No. 4
sieve and less than 2Yo 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 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 areathat 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, be protected from wetting and hydrostatic pressure buildup by an underdrain
system.
The drains should consist of rigid perforated PVC 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 lYoto a suitable gravrty outlet. Free-draining granular material used in the
underdrain system should contain less than 2o/o passing the No. 200 sieve, less than 50olo passing
the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at
least 1lzfeetdeep.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the ADU and garage have 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 95Yo 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 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 10 feet in pavement and walkway ireas. A swale may be
needed to direct surface runoff around the building.
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 1
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.
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 veri$'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 mdy be of further assistance, please let us know.
Respecttully Submitted,
Kumar & Associates,
James H. Parsons,
Reviewedby:
b '!
Daniel E. Hardin, P.E.
JHPikac
attachments Figure I - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Gradation Test Results
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586C{t
u/1m
VICINITY MAP
NOT TO SCALE
SITE
EAGLE
GYPSUM1o
,*"*nO"
G,r"ENWooD
SPRINGS
SWEETWATER RD
&
Pfi2
PIT I:
150 o 150
7280.(es0
151
"rou*tt *ono
APPROXIMATE SCALE_FEET
PIT 1 PROFILE PIT 1 PROFILE PIT 2
F
TJ
trJl!
I-F(L
LIla
F
Lrl
LrJl!
I:rFfLLIo
0
5
'10
LEGEND
-l WC=3.7
| ++=st- -2OO=23
0
5
10
t
TOPSOTL; SAND, SCATTERED GRAVEL, SILTY, ORGANICS, FIRM, SLIGHTLY MOIST, BROWN AND
GRAY.
GRAVEL AND COBBLES (GM); SCATTERED BOULDERS, SILTY, SANDY, SLIGHTLY CALCAREOUS,
MEDIUM DENSE TO DENSE, SLIGHTLY MOIST, BROWN AND GRAY.
DISTURBED BULK SAMPLE
PRACTICAL REFUSAL TO THE EXCAVATION
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON OCTOBER 14, 2024.
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 NOT MEASURED AND THE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPTH.
4. THE EXPLORATORY PIT LOCATIONS 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. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D A22);
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140).
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Fig. 224-7-559 Kumar & Associates LOGS OF EXPLORATORY PITS
HYDROMETER ANALYSIS
U.S. SIANDND SERIES Cff SQUARE OPENING:i
alA.t/^'it/r.2I HRS 7 HRS6 ltN ta vtN 60v1tr avtf,
TIME RMINOS
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DIAMETER OF INM
CLAY TO SILT
GRAVEL 51 X SAND 26 X
UQUID LIMIT - PLASTICIW INDEX
SAMPLE OF: Sllly Sondy Grovel wllh Cobbles
COBBLES
SILT AND CI.AY 23 X
FROM:Plt1O2'-5.5'
Th.!. Lll rolulls qpply only lo lh6
sompl$ whlch wcre lollod, Tho
iorllng report lhqll nol bc rcprcduccd,
lxccpl ln tull, wllhout lh. wrlll.n
opprwol ol Kumor & A!!mlolc!, lnc.
Slcvc onolysls llsllng ls plrfomld ln
qccordonco wlth ASTM D6913, ASTI, 07928,
ASTII C136 cnd/or ASTM Dll,00.
Fig. 3
SAND GRAVEL
FINE MEDTUM ICOARSE FINE COARSE
E 24-7-559 Kumar & Associates GRADATION TEST RESULTS