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Kumar & Associates, Inc.®
Geotechnical and Materials Engineers
and Environmental Scientists
An Employee Owned Company
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
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 32, PINYON MESA
TBD CLIFFROSE WAY
GARFIELD COUNTY, COLORADO
PROJECT NO. 20-7-343
JULY 13, 2020
PREPARED FOR:
DOOLEN CONSTRUCTION
ATTN: DAVE DOOLEN
3838 COUNTY ROAD 243
NEW CASTLE, COLORADO 81647
dave(a,doolenconstruction.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1 -
SUBSIDENCE POTENTIAL - 2 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 3 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 4 -
FOUNDATIONS - 4 -
FOUNDATION AND RETAINING WALLS - 5 -
FLOOR SLABS - 6 -
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAINAGE - 7 -
LIMITATIONS - 7 -
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2 - LOG, LEGEND AND NOTES OF EXPLORATORY BORING
FIGURE 3 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. ° Project No. 20-7-343
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot 32, Pinyon Mesa, Cliffrose Way, 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 Doolen Construction dated June 12, 2020.
An exploratory boring was drilled 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, compressibility or swell and other engineering characteristics. The results of
the field exploration and laboratory testing were 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
The proposed residence will be a one and two story structure with attached garage. Ground floor
will be structural over crawlspace for the living areas and slab -on -grade for the garage. Grading
for the structure is assumed to be relatively minor with cut depths between about 2 to 6 feet. We
assume relatively light foundation loadings, typical of the proposed type of construction.
If building loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The subject site was vacant at the time of our field exploration. The site slopes down to the
northwest at grades of about 7 to 10 percent. Elevation difference across the lot is estimated at
10 feet and across the building area is estimated at 4 feet. Vegetation consists of grass weeds
and sage brush.
Kumar & Associates, Inc. ® Project No. 20-7-343
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SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Pinyon Mesa
development. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and
siltstone with some massive beds of gypsum and limestone. There is a possibility that massive
gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the lot.
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, several sinkholes were
observed scattered throughout the lower Roaring Fork River Valley. These sinkholes appear
similar to others associated with the Eagle Valley Evaporite in areas of the Eagle Valley.
Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities
was encountered in the subsurface materials; however, the exploratory borings were relatively
shallow, for foundation design only. Based on our present knowledge of the subsurface
conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of
future ground subsidence on Lot 32 throughout the service life of the proposed residence, in our
opinion, is low; however, the owner should be made aware of the potential for sinkhole
development. If further investigation of possible cavities in the bedrock below the site is desired,
we should be contacted.
FIELD EXPLORATION
The field exploration for the project was conducted on June 19, 2020. One exploratory boring
was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The boring
was advanced with 4 inch diameter continuous flight augers powered by a truck -mounted CME -
45B drill rig. The boring was logged by a representative of Kumar & Associates, Inc.
Samples of the subsoils were taken with a 2 inch I.D. spoon sampler. The sampler was driven
into the subsoils at various depths with blows from a 140 pound hammer falling 30 inches. This
test is similar to the standard penetration test described by ASTM Method D-1586. The
penetration resistance values are an indication of the relative density or consistency of the
subsoils. Depths at which the samples were taken and the penetration resistance values are
shown on the Log, Legend and Notes of Exploratory Boring, Figure 2. The samples were
returned to our laboratory for review by the project engineer and testing.
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SUBSURFACE CONDITIONS
A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The
subsoils consist of about 11/2 feet of topsoil overlying stiff to very stiff sandy silt and clay down
to the maximum explored depth of 51 feet.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and gradation analyses. Results of swell -consolidation testing performed on relatively
undisturbed drive samples, presented on Figure 3, indicate low to moderate compressibility
under existing moisture conditions and light loading and a low expansion potential when wetted.
The laboratory testing is summarized in Table 1.
No free water was encountered in the boring at the time of drilling later and the subsoils were
slightly moist to moist.
FOUNDATION BEARING CONDITIONS
The sandy silt and clay soils encountered in this area typically possess low bearing capacity and
low to moderate collapse potential (settlement under constant load) when wetted. Laboratory
testing indicated a low expansion potential when wetted. A shallow foundation placed on these
soils will have a risk of movement if the soils become wet and care should be taken in the
surface and subsurface drainage around the house to prevent the soils from becoming wet. It will
be critical to the long term performance of the structure that the recommendations for surface
drainage and subsurface drainage contained in this report be followed. The amount of
movement, if the bearing soils become wet, will be related to the depth and extent of subsurface
wetting. Removing and replacing at least 5 feet of the onsite material as compacted structural fill
is recommended as preparation of the foundation subgrade. The exposed soils in the excavation
should be further evaluated at the time of excavation.
Movement in the event of subsurface wetting could cause building distress and mitigation such
as a deep foundation, such as piles or pier extending down below roughly 30 to 35 feet deep or a
heavily reinforced mat foundation, on the order of 2 feet thick could be used as a less risky
alternative to support the proposed house. If a deep foundation or mat foundation is desired, we
should be contacted to provide further design recommendations.
Kumar & Associates, Inc. ° Project No. 20-7-343
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DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the nature of
the proposed construction, the building can be founded with spread footings bearing on a
minimum 5 feet of compacted structural fill with a risk of settlement, particularly if the bearing
soils become wet, accepted by the owner. Control of surface and subsurface runoff will be
critical to the long-term performance of a shallow spread footing foundation system.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on a minimum 5 feet of compacted structural fill should be
designed for an allowable bearing pressure of 1,200 psf. Based on experience, we
expect initial settlement of footings designed and constructed as discussed in this
section will be about 1 inch or less. Additional movement could occur if the
bearing soils become wet. A 1/3 increase in the allowable bearing pressure can be
taken for toe pressure of eccentrically loaded footings.
2) The footings should have a minimum width of 20 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 heavily reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 14 feet.
The foundation should be configured in a "box like" shape to help resist
differential movements. 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) The topsoil and any loose or disturbed soils should be removed from the building
area down to a depth of at least 5 feet below footing grade. The exposed soils in
the footing area should then be moistened and compacted. Structural fill should
Kumar & Associates, Inc. ° Project No. 20-7-343
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consist of a low permeable soil, such as the on-site silt and clay, compacted to at
least 98% standard Proctor density within 2% of optimum moisture content.
6) A representative of the geotechnical engineer should observe all footing
excavations and provide compaction testing of structural fill prior to concrete
placement.
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 55 pcf for backfill consisting
of the on-site fine-grained 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 45 pcf for backfill consisting of the on-site fine-grained 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 95% of the maximum standard Proctor density. Care
should be taken not to overcompact the backfill or use large equipment near the wall, since this
could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall
backfill should be expected, even if the material is placed correctly, and could result in distress to
facilities constructed on the backfill.
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 bottoms of the footings can be calculated
Kumar & Associates, Inc. ° Project No. 20-7-343
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based on a coefficient of friction of 0.30. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 325 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 nonexpansive material compacted to at
least 95% 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 with a movement risk similar to that described above in the event of wetting of the
subgrade soils. 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 relatively
well graded sand and gravel such as road base should be placed beneath floor slabs to limit
capillary moisture rise. This material should consist of minus 2 -inch aggregate with at least 50%
retained on the No. 4 sieve and less than 12% passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95% 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.
UNDERDRAIN SYSTEM
It is our understanding the proposed ground floor elevation is near the surrounding grade and that
crawlspace is relatively shallow, around 3 feet. Therefore, a foundation drain system is not
recommended. 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 condition. If a basement level is proposed, we recommend an
underdrain be provided to protect the lower level from wetting and hydrostatic pressure buildup.
Kumar & Associates, Inc. ° Project No. 20-7-343
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If the finished floor elevation of the proposed residence is revised to have a deep crawlspace or a
floor level below the surrounding grade, we should be contacted to provide recommendations for
an underdrain system. All earth retaining structures (site walls) should be properly drained.
SURFACE DRAINAGE
It will be critical to the building performance to keep the bearing soils dry. 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 95% of the maximum standard Proctor density in pavement and slab areas
and to at least 90% 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 (if any)
should be 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.
5) Landscaping which requires regular heavy irrigation should be located at least 10
feet from foundation walls. Consideration should be given to use of xeriscape to
reduce the potential for wetting of soils below the building caused by irrigation.
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 boring drilled at the location indicated on Figure 1, the proposed type of
construction and our experience in the area. Our services do not include determining the
Kumar & Associates, Inc. ° Project No. 20-7-343
8
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 boring 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.
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 verify 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.
Respectfully Submitted,
Kumar & Associates, Inc.
James H. Parsons, E.I.
Reviewed by:
Daniel E. Hardin,
JHP/kac
Kumar & Associates, Inc.
Project No. 20-7-343
Lot 24
10.2' —
1
Set 18" #5 Rebar and
1-1/4" Orange Plastic Cap
tamped "PROP COR PLS 36572"
Fence
( Typical)
Lot 31
Lot 23
I—x
—12.5'\
�N 90°01'00' E! 68.50
Set 18" #5 Rebar and
1- /4" Orange Plastic Cap
am_p_ed "PROP COR PLS 3657.
Found #5 Rebar an
1-1/4" Orange Plastic C
stamped "PROP COR PLS 36572'
Sewer Stub
(Type
Curb & Gutter
15 0 15 30
APPROXIMATE SCALE -FEET
Cli Erose
W
Lot 33
Fo nd #5 Rebar and
I /4" Orange Plastic Cap
tamped 'PROP COR PLS 36572
Site Benchmark = 6259.1'
Water Service (Typical)
Telephone Pedestal (Ty,
5
SE
.iv»>vr Ain ti
20-7-343
Kumar & Associates
LOCATION OF EXPLORATORY BORING
Fig. 1
Subsoil Siudy, Proposed Residence \ Drafting \207343-02.dwg
DEPTH -FEET
0
BORING 1
EL. 6255'
/
5 / 18/12
WC=5.4
DD=104
/
10 // 24/12
/
/ 33/12
1 5WC=6.3
� DD=108
—200=84
/
20 /27/12
WC=6.0
DD=107
/
/ 37/12
25WC=6.2
� DD=115
—200=86
/
30 20/12
WC=7.7
DD=104
40
45
50
35/12
/
/
/
/
25/12
LEGEND
TOPSOIL; SAND, SILTY, SLIGHTLY CLAYEY, ORGANIC MATTER, FIRM,
SLIGHTLY MOIST, BROWN.
SILT AND CLAY (ML—CL); SANDY TO VERY SANDY, VERY STIFF TO
HARD, SLIGHTLY MOIST, BROWN.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
18/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 18 BLOWS OF
A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED
TO DRIVE THE SAMPLER 12 INCHES.
NOTES
1. THE EXPLORATORY BORING WAS DRILLED ON JUNE 19, 2020 WITH
A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER.
2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED
APPROXIMATELY BY TAPING FROM FEATURES SHOWN ON THE SITE
PLAN PROVIDED.
3. THE ELEVATION OF THE EXPLORATORY BORING WAS OBTAINED
BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN
PROVIDED.
4. THE EXPLORATORY BORING LOCATION AND ELEVATION SHOULD BE
CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE
METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY
BORING LOG REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN
MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE
TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
—200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
20-7-343
Kumar & Associates
LOG, LEGEND AND NOTES OF
EXPLORATORY BORING
Fig. 2
Proposed Residence\Drat
CONSOLIDATION - SWELL
CONSOLIDATION
0
—1
— 2
— 3
— 4
2
1
0
— 1
— 2
— 3
SAMPLE OF: Sandy Silt and Clay
FROM: Boring 1 CSD 5'
WC = 5.4 %, DD = 104 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
1.0 APPLIED PRESSURE - KSF
10
100
SAMPLE OF: Clayey Sand and Silt
FROM: Boring 1 CSD 20'
WC = 6.0 %, DD = 107 pcf
These test results apply only to the
samples tested. The testing report
shall not be reproduced, except in
full, without the written approval of
Kumar and Associates, Inc. Swell
Consolidation testing performed in
accordance with ASTM D-4546.
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
1.0 APPLIED PRESSURE - KSF
10
100
20-7-343
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 3
It+A
Kumar & Associates, Inc®
Geotechnical and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 20-7-343
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(pcf)
GRADATION
PERCENT
PASSING 200 SIEVE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(psf)
SOIL TYPE
BORING
DEPTH
(ft)
GRAVEL
(%)
SAND
(%)
LIQUID LIMIT
(%)
PLASTIC
INDEX
(%)
1
5
5.4
104
Sandy Silt and Clay
15
6.3
108
84
Sandy Silt and Clay
20
6.0
107
Clayey Sand and Silt
25
6.2
115
86
Sandy Silt and Clay
30
7.7
104
Sandy Silt and Clay