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March 17,2021
Richard and Leann Katchuk
12 Primrose Lane
Carbondale, Colorado 81 623
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COMr'i.iil r]'Y 0t\,ELJpMENT
Project No.2L-7-220
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot26, Filing 9, Elk
Springs, 0129 Kingbird Drive, Garfield County, Colorado
Richard and Leann:
As requested, Kumar & Associates performed a subsoil study for design of foundations at the
subject site. The study was conducted in accordance with our agreement for professional
services to you dated February 26,2021. The data obtained and our recommendations based on
the general proposed construction and subsurface conditions encountered are presented in this
report.
Proposed Construction: Development plans for the proposed residence were not available at
the time of our study. We understand the residence will be located within the building envelope
shown on Figure 1. We assume the structure will be one or two stories with a structural floor
over crawlspace or slab-on-grade. Cut depths are assumed to range between about 2 to 6 feet.
Foundation loadings for this type of construction are assumed to be relatively light and typical of
the proposed type of construction.
If building location, grading or foundation loading is significantly different than described, we
should be notified to re-evaluate the recommendations presented in this report.
Site Conditions: The site is currently vacant and located near the top of a hillside, generally
sloping down to the west at a gentle to moderate grade. Vegetation at the site consists of native
grass, sage brush and juniper and pinon trees. Patchy snow covered the lot at the time of our
field exploration.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
three exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. T1rre subsoils encountered, below about a foot of topsoil (silty clayey sand
and basalt rock), consist of basalt cobbles and boulders in a highly calcareous sandy silt and
-2-
rock matrix. Results of gradation testing performed on a disturbed sample of the matrix soil are
presented on Figure 3. No free water was observed in the pits at the time of excavation and the
soils were slightly moist.
Preliminary 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, basalt rock soils designed for an allowable soil
bearing pressure of 2,500 psf for support of the proposed residence. The upper organi c/topsoil
layer has variable compression potential and should be removed from below building areas. Our
experience in this area indicates that the basalt rock soil can be excavated a few feet with a
heavy-duty trackfioe but rock excavation techniques could also be needed such as for deeper cuts
and trenches. 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 basalt rock soils. Voids created from boulder removal at footing grade
should be backfilled with concrete or a structural material such as road base compacted to at least
98 percent of standard Proctor density at a moisture content near optimum. Exterior footings
should be provided with adequate cover above their bearing elevations for frost protection.
Placement of footings at least 3 6 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 a lateral earth pressure based on al equivalent fluid unit
weight of at least 50 pcf for the on-site soil as backfill excluding organics and rock larger than
6 inches or imported gtanular material such as road base.
Floor Slabs: The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded
slab-on-grade construction. The subgrade should be evaluated for slab support and possible need
for structural fill such as road base. 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 c.racking. The requirements fbr 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 below grade 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 2% passing the No. 200 sieve.
Kumar & Associates, lnc. s Project No,21.7.220
-J-
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 or imported road base.
Underdrain System: Although free water was not encountered during our exploration, it has
been our experience in mountainous areas that 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 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% to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2% passing the 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 l% 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 of the 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 90%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 surrounding the exterior of the building should be sloped to
drain away frorn 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.
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.
Kumar & Associates, lnc. rr Project No.21-7-220
4-
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 recoflrmendations submitted in this report are based
upon the data obtained from the expioratory pits excavateci at the locations indicated on Figure I
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, 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
expioratory pits and variations in the subsurf'ace 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 verifu that the reoommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or mo<lifieations to the reeomme.ndations 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,
€{q*$laar r cg ;t ss**isa**:"q" Eeec"
Steven L. Pawlak, P.E.
Reviewed by:
Daniel E. Hardin, P. E.
SLPlkac
Attachments: Figure I - Location of Exploratory Pits
Figure 2 -Logs of Exploratory Pits
Figure 3 - Gradation Test Results
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21 -7 -220 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
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LEGEND
TOPSOIL; SILTY CLAYEY SAND AND BASALT COBBLES AND BOULDERS, ROOT ZONE' BROWN
BASALT CoBBLES AND BOULDERS (GM); CALCAREOUS SILT MATRIX, DENSE, SLIGHTLY MOIST,
MIXED PALE-BROWN.
DISTURBED BULK SAMPLE
t PRACTICAL DIGGING REFUSAL, WHERE SHOWN ABOVE BOTTOM OF PIT, INDICATES THAT
MULTIPLE ATTEMPTS WHERE MADE TO ADVANCE THE HOLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON MARCH 9' 2021'
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY TAPING FROM
STAKED BUILDING ENVELOPE CORNERS.
3. 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
IMI'LILU tsT INtr MtrIN\JU UJE.I,''
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.
LABORATORY TEST RESULTS:
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTU O +ZZ);
-?:QO= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1 1 a0);
Fig. 2LOGS OF EXPLORATORY PITSKumar & Associates21 -7 -224
7
HYDROMETER ANALYSIS
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IOFPIN MI
SAND GRAVEL COBBLESCLAY TO SILT MEDIUM FINE COARSE
GRAVEL 47 % SAND
LIQUID LIMIT
SAMPLE 0F: SlllY SondY Grovel
39'4
PLASTICIW INDEX
SILT AND CLAY 14 %
FROM: Plt 5 O 1'-2'
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ASTM C136 ondlor ASTM Dll'10'
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Fis. 3GRADATION TEST RESULTSKumar & Associates21*7-224