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5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusacom
An Employeo OryYncd ComPonY www.kumarusa.com
Office l-ocations: Denver (HQ), Par{<er, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
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SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
29 SPIRIT MOUNTAIN ROAD
LOT 19, CORYELL RANCH
GARFTELD COUNTY, COLORADO
FEB t I 2025
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PROJECT NO.24-7-169
MARCH 20,2024
PRBPARED X'OR:
ALIUS DESIGN GROUP
ATTN: MICHAEL EDINGER
108 DIAMOND A RANCH ROAD
CARBONDALE, COLORAD O 81623
michael@aliusdc.com
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TABLE OF'CONTENTS
PURPOSE AND SCOPE OF STUDY............
PROPOSED CONSTRUCTION ...
SITE CONDITIONS.....
SUBSIDENCE POTENTIAL
FIELD EXPLORATION
SUBSURFACE CONDITIONS
DESIGN RECOMMENDATIONS
FOLINDATIONS
FOLINDATION AND RETAINING WALLS
FLOOR SLABS
LINDERDRAIN SYSTEM
SURFACE DRAINAGE...
LIMITATIONS
FIGURE I - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - GRADATION TEST RESULTS
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Kumar & Associates, Inc. o Project No. 2+7-169
PURPOSE AND SCOPE OF'STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on
Lot 19, Coryell Ranch, 29 Spirit Mountain Road, Garfield County, Colorado. The project site
is shown on Figure 1. The purpose of the study was to develop recommendations for the
foundation design. The study was conducted in accordance with our agreement for geotechnical
engineering services to Alius Design Group dated February 23'2024.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils obtained during the field
exploration were tested in the laboratory to determine their classification. The results of the field
exploration and laboratory testing werc analyzed to develop recommendations for foundation
types, depths and allowable pressures for the proposed building foundation. This report
summarizes the data obtained during this study and presents our conclusions, design
recommendations and other geotechnical engineering considerations based on the proposed
construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
We assume the proposed residence will be a two-story structure. Ground floor will be structural
over crawlspace or slab-on-grade. Grading for the structure is assumed to be relatively minor
with cut depths between about 3 to 10 feet. We assume relatively light foundation loadings,
typical of the proposed type of construction.
When building location, grading and loading information have been developed, we should be
notified to re-evaluate the recommendations presented in this report.
SITE CONDITIONS
The site was vacant with no snow at the time of our field work. The site is vegetated with grass
and weeds and slopes gently down to the east. The Roaring Fork River is located about 600 feet
northeast from where the borings were drilled. Nearby lots are developed with one to two-story
residences.
SUBSIDENCE POTENTIAL
Coryell Ranch is underlain by Pennsylvania Age Eagle Valley Evaporite bedrock. The evaporite
contains gypsum deposits. Dissolution of the gypsum under certain conditions can cause
sinkholes to develop and can produce areas of localized subsidence. During previous work in
the area by others, sinkholes were identified in Coryell Ranch development but not observed in
area of this building. Based on our present knowledge of the site, it cannot be said for certain
that sinkholes will not develop. In our opinion, the risk of ground subsidence in the building
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area of Lot 19 is low and similar to other lots in the area without sinkholes but the owner should
be aware of the potential for sinkhole development.
F'IELD EXPLORATION
The field exploration for the project was conducted on March 14,2024. Two exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions.
The borings were advanced with 4 inch diameter continuous flight augers powered by a track-
mounted CME 45 drill rig. The borings were logged by a representative of Kumar & Associates,
Inc.
Samples of the subsoils were taken with a l% inch I.D. spoon sampler. The sampler was driven
into the subsoils at various depths with blows fiom a 140 pound hammer falling 30 inches. This
test is similar to the standard pcnctration tcst described by ASTM Method D-1586. The
penetration resistance values are an indication of the relative density of the subsoils. Depths at
which the sarnples were taken and the penetration resistance values are shown on the Logs of
Exploratory Borings, Figure '2. 'l'he samples were returned to our laboratory tbr review by the
project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about Yz foot of topsoil overlying relatively dense silty sandy gravel with
cobbles and probable boulders. Drilling in the dense granular soils with auger equipment was
difficult due to the cobbles and boulders and drilling refusal was encountered in the deposit.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and gradation analyses. Results of gradation analyses performed on small diameter drive
samples (minus l%-inch fraction) of the coarse granular subsoils are shown on Figure 3.
No free water was encountered in the borings at the time of drilling. Ground water is expected
to be relatively deep and well below basement level at this site. The subsoils were slightly moist.
DESIGN RECOMMENDATIONS
FOI.INDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the natural granular soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
l) Footings placed on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 4,000 psf. Based on experiencs, we expect
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settlement of footings designed and constructed as discussed in this section will
be about I inch or less.
2) The footings should have a minimum width of 16 inches for continuous walls and
2 feet for isolated Pads.
3) Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
of foundations at least 36 inches below exterior grade is typically used in this
area.
4) Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 10 feet.
Foundation walls acting as retaining structures should also be designed to resist
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this rePort.
5) All existing fill (if any), topsoil and any loose or disturbed soils should be
removed and the footing bearing level extended down to the relatively dense
natural granular soils. The exposed soils in footing area should then be moistened
and compacted.
6) A representative ofthe geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOUNDATION AND RETAINING WALLS
Foundation walls and retaining structures which are laterally supported and can be expected
to undergo only a slight amount of deflection should be designed for a lateral earth pressure
computed on the basis of an equivalent fluid unit weight of at least 45 pcf for backfill consisting
of the on-site granular soils. Cantilevered retaining structures which are separate from the
residence and can be expected to deflect sufficiently to mobilize the full active earth pressure
condition should be designed for a lateral earth pressure computed on the basis of an equivalent
fluid unit weight of at least 40 pcf for backfill consisting of the on-site granular soils.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction materials and equipment.
The pressures recommended above assume drained conditions behind the walls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure buildup behind walls.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at a moisture content near optimum. Backfill in pavement and walkway
areas should be compacted to at least 95o/o of the maximum standard Proctor density. Care
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should be taken not to overcompact the backfill or use large equipment near the wall, since this
oould cause excessive lateral pressure on the wall. Some settlement of deep foundation wall
backfill should be expeoted, even if the material is placed correctly, and could result in distress
to facilities constructed on the backfill. Backfill should not contain organics, debris or rock
larger than about 6 inches.
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resistance of the footing on the foundation materials and passive earth pressure against
the side of the footing. Resistance to sliding at the boffoms of the footings can be calculated
based on a coefficient of friction of 0.50. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 350 pcf. The
coefficient of friction and passive pressure values recommended above assume ultimate soil
strength. Suitable factors of safety should be included in the design to limit the strain which will
occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads should be a granular material compacted to at least
95%o of the maximum standard Proctor density at a moisture content near optimum.
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 at least 50% retained on the No. 4 sieve
and less than2o/o passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at \east95%n of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
on-site granular soils devoid of vegetation, topsoil and oversized rock.
LINDERDRAIN SYSTEM
Althouigh free waierwas not eircouniereri during our expioration, 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 runoffcan create a perched
condition. We recommend below-grade construction, such as retaining walls, crawlspace and
basement areas, be protected from weffing and hydrostatic pressure buildup by an underdrain
system.
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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 lYo
to a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain
system should contain less than 2%o passingthe No. 200 sieve, less than 50% passing the No. 4
sieve and have amaximum size of 2 inches. The drain gravel backfill should be at least lYzfeet
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 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 95o/o 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.
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 paved areas. Free-draining wall backfill should be
covered with filter fabric and capped with about 2 feet of the on-site soils to
reduce surface water infiltration.
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 atthis 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 borings drilled excavated at the locations indicated on Figure l, 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 borings 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 so that re-evaluation of the recommendations may be made.
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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 om information. As the project evolvcs, we
should provide continued consultation and field services during construction to review and
monitorthe implementation of ourrecommendations, 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.
Respectfu lly Submitted,
Kumar & Associates, lnc.
Daniel E. Hardin, P.E.
Reviewutl by:
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Steven L. Pawlak, P.E.
DEH/kac
Kumar & Associates, lnc.6 Proiect No. 24-7-169
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LEGEND
TOPSOIL; ORGANIC SILTY SAND, GRAVELLY, FIRM, MOIST, DARK BROWN.
GRAVEL (0U); WtrH COBBLES, PROBABLE BOULDERS, SANDY, SILTY, DENSE, SLIGHTLY MOIST,
BROWN.
i DRrvE sAMpLE, 1 s/8-rNcH t.D. spLtT spooN STANDARD PENETRAT|oN TEST.
q67a DRIVE SAMPLE BLOW COUNT. INDICATES THAT 50 BLOWS OF A 14O-POUND HAMMER-_, FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 4 INCHES.
t PRACTICAL AUGER REFUSAL.
NOTES
1, THE EXPLORATORY BORINGS WERE DRILLED ON MARCH 14,2024 WITH A 4_INCH_DIAMETER
CONTINUOUS-FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER
TO THE GROUND ELEVATION AT BORING 1 AS 1OO FEET.
4. THE EXPLORATORY BORING 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 BORING LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ISTV OOSIS);
-200= PERCENTAGE PASSING No. 200 SIEVE (ASTM D1140).
\NC=2,4
+4=25
-200-23
24-7-169 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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DIAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT COBBLES
GRAVEL 25 X SAND
LIQUID LIMIT
SAMPLE OF: Cloyey Silty Grovelly Sond
52X
PI-ASTICITY INDEX
SILT AND CLAY 23 X
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MEDIUM COARSE FINE COARSEFINE
Fig. 5GRADATION TEST RESULTS24-7 -1 69 Kumar & Associates