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Kutner & Assoc 1 , Ilnc.
Geotechnical and Materials Engineers
and Environmental Scientists
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employee Owned Company www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
y ASSOrrary
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 68, FILING 2, PINYON MESA
PINYON MESA DRIVE
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-221
MAY 6, 2019
PREPARED FOR:
PMGC2, LLC
ATTN: RON NORMAN
6300 RIGLEA PLACE, SUITE 900
FORT WORTH, TEXAS 76116
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TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 2 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FLOOR SLABS - 4 -
UNDERDRAIN SYSTEM - 5 -
SURFACE DRAINAGE - 5 -
LIMITATIONS - 6 -
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2 - LOG OF EXPLORATORY BORING
FIGURE 3 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. Project No. 19-7.221
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
68, Filing 2, Pinyon Mesa, Pinyon Mesa Drive, Garfield County, Colorado. The project site is
shown on Figure 1. The purpose of the study was to develop recommendations for foundation
design. The study was conducted in accordance with our agreement for geotechnical engineering
services to PMGC2, LLC, dated April 8, 2019.
A field exploration program consisting of an exploratory boring was conducted to obtain
information on 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 subsoil conditions
encountered.
PROPOSED CONSTRUCTION
At the time of our study, design plans for the residence had not been developed. The building is
proposed in the area of the exploratory boring location shown on Figure 1. Similar to the other
residences proposed in the development, we assume basement or below grade levels will not be
constructed. Grading for the structure is assumed to be relatively minor with cut depths between
2 and 3 feet. For the purpose of our analysis, foundation loadings for the structure were assumed
to be relatively light and typical of the proposed type of construction.
When building loadings, location and grading plans are available, we should be notified to re-
evaluate the recommendations contained in this report.
SITE CONDITIONS
The property was vacant at the time of our exploration. The boring was drilled within the
building area. The site is vegetated with grass and weeds and scattered sagebrush. The ground
Kumar & Associates, Inc. Project No. 19-7-221
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surface is relatively flat and slopes gently down to the northwest with about 3 feet of elevation
difference across the building area. A natural dry drainage is located between Paintbrush Drive
to the northeast and Pinyon Mesa Drive.
FIELD EXPLORATION
The field exploration for the project was conducted on April 17, 2019. One exploratory boring
was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The boring
was advanced with a 4-inch diameter continuous flight auger powered by a truck -mounted CME-
45B drill rig. The boring was logged by a representative of Kumar & Associates.
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 of Exploratory Boring, Figure 2. The samples were returned to our laboratory
for review by the project engineer and testing.
SUBSURFACE CONDITIONS
A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The
subsoils consist approximately 6-inches of topsoil, underlain by stiff to very stiff, sandy clay and
silt from 'A to 10 feet, underlain by very stiff, sandy clay from 10 to 23 feet, underlain by dense,
silty, clayey, sand and gravel from 23 to 32 feet, underlain by dense/hard sand and silt down to
36 feet. The soils encountered in the boring are variable and generally similar to the soils
encountered at other nearby lots.
Laboratory testing performed on samples obtained during the field exploration included natural
moisture content and density, and percent fines (percent passing the No. 200 sieve). Swell -
consolidation testing was performed on relatively undisturbed drive samples of the silt and clay
subsoils. The swell -consolidation test results, presented on Figure 3, indicate low
compressibility under relatively light surcharge loading. The samples of sandy silt and clay and
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sandy clay from 5 and 15 feet showed a low expansion or collapse potential when wetted under a
constant light surcharge load. The laboratory testing is summarized in Table 1.
No free water was encountered in the boring at the time of drilling and the subsoils were slightly
moist.
FOUNDATION BEARING CONDITIONS
The sandy silt and clay soils encountered at expected shallow cut depth tend to settle when they
become wetted.
A shallow foundation placed on the sandy silt and clay soils will have a high
risk of settlement if the subsoils become wetted. It will be critical to the long-term performance
of the structure that the recommendations for surface grading and drainage contained in this
report be followed to limit potential wetting of the bearing soils. The amount of settlement, if
the bearing soils become wet, will mainly be related to the depth and extent of subsurface
wetting. Settlement in the event of subsurface wetting could be 1 to 2 inches and likely cause
building distress. Mitigation methods such as deep compaction, a deep foundation (such as piles
or piers extending down around 25 feet below existing ground surface) or a heavily reinforced
mat foundation designed by the structural engineer can be used to support the proposed house
with a lower risk of settlement. Presented below are recommendations for shallow spread
footings and slab -on -grade floor bearing on compacted structural fill. If a deep foundation or
mat foundation is desired, we should be contacted to provide further design recommendations.
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
compacted structural fill with a risk of settlement and possible building distress.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1)
Footings placed on at least 3 feet of compacted structural fill should be designed
for an allowable bearing pressure of 1,500 psf. Based on experience, we expect
initial settlement of footings designed and constructed as discussed in this section
Kumar & Associates, Inc. Project No. 19-7-221
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will be about 1 inch or less. Additional settlement on the order of 1 to 2 inches
could occur if deep wetting of the subsoils were to occur.
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.
Foundation walls acting as retaining structures should also be designed to resist a
lateral earth pressure corresponding to an equivalent fluid unit weight of at least
55 pcf.
5) The topsoil and any loose or disturbed soils should be removed in the building
area. The natural silt and clay soils in footing areas should be sub -excavated to at
least 3 feet below design bearing level and to at least 1'/z feet beyond footing
edges. The exposed soils in footing area should then be moistened and
compacted. Structural fill can consist of the onsite silt and clay soils compacted
to at least 98% of standard Proctor density at near optimum moisture content.
6) A representative of the geotechnical engineer should conduct compaction testing
during structural fill placement and observe all footing excavations prior to
concrete placement to evaluate bearing conditions.
FLOOR SLABS
The natural on -site soils, exclusive of topsoil, can be used to support lightly loaded slab -on -grade
construction with a risk of settlement similar to that for spread footings. 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 interior slabs for support. This material should consist of
Kumar & Associates, Inc. Project No.19-7.221
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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 silty soils or a suitable imported granular soil 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 condition. We
recommend below -grade construction such as basement areas be protected from wetting and
hydrostatic pressure buildup by an underdrain system. Slab -on -grade areas and crawlspaces less
than 4 feet deep should not be provided with an underdrain.
Where needed, 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 1 foot below lowest adjacent finish grade and
sloped at a minimum 1 % 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 11/2 feet deep. An impervious membrane such as 20 mil PVC should be placed beneath the
drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting
of the bearing soils.
SURFACE DRAINAGE
Providing proper surface grading and drainage will be critical to keeping the bearing soils dry
and limiting potential for building settlement and distress. 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.
Kumar & Associates, Inc. Project No. 19-7-221
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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 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.
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
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 to be 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
Kumar & Associates, Inc. Project No. 19.7.221
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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 of 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.
Sincerely,
Kumar & Associates, Inc.
44,44,4
Shane J. Robat, P.E.
Project Manager
Reviewed by:
Steven L. Pawlak,
SJR/kac
cc: F&M Architec (mike@iyfandmarchitects.com)
Kumar & Associates, Inc. Project No. 19-7-221
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APPROXIMATE SCALE -FEET
Con
19-7-221C
Kumar & Associates
LOCATION OF EXPLORATORY BORING
Fig. 1
DEPTH -FEET
— 0
- — 5
10
— 15
— 20
-- 25
— 30
35
— 40
BORING 1/68 LEGEND
EL. 6196'
16/12
13/12
WC=6.1
DD=98
21/12
WC=9.5
DD=108
—200=89
17/12
WC=6.9
DD=102
35/12
WC=5.1
DD=109
—200=85
43/12
56/12
7
F
779
x"9
TOPSOIL; ORGANIC, CLAY AND SILT, FIRM, BROWN, MOIST.
CLAY AND SILT (CL—ML); SANDY, STIFF TO VERY STIFF,
SLIGHTLY MOIST, TAN, SLIGHTLY CALCAREOUS WITH DEPTH.
CLAY (CL); SANDY, VERY STIFF, TAN, SLIGHTLY MOIST, TAN,
CALCAREOUS WITH DEPTH.
GRAVEL AND SAND (GM, SM); SILTY, CLAYEY, DENSE, SLIGHTLY
MOIST, TAN.
SAND AND SILT (SM—ML); DENSE/HARD, MOIST, TAN.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
16/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 16 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 APRIL 17, 2019 WITH
A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER.
2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED
APPROXIMATELY BY PACING 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).
19-7-221C
Kumar & Associates
LOG OF EXPLORATORY BORING
Fig. 2
CONSOLIDATION - SWELL
CONSOLIDATION - SWELL
1
0
—1
— 2
— 3
— 4
1
0
— 1
— 2
— 3
4
SAMPLE 0F: Sandy Silt and Clay
FROM: Boring 1/68 ® 5'
WC = 6.1 %, DD = 98 pcf
rill I I i I l
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
I
1.0 APPLIED PRESSURE — KSF 10
SAMPLE OF: Sandy Clay
FROM: Boring 1/68 ® 15'
WC = 6.9 %, DD = 102 pcf
>ne.s u.e r.eea.lrop6y wet to e
erg. rn. r.pon
'ha•e S. ,.pehe.d...c.pe In
tor, .Ultent rn..ntten ,ppr,,,, of
x,e er nna a.cc1cne., Hp. rill
Cnninklt tyn loinyfl p.re.rrfl.t{ in
ntnordcnc.:dh 0- 546.
10 APPLIED PRESSURE — KSF 10
100
L..
I
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
i 1 ; I 1_. j t I i
100
19-7-221C
6
Kumar & Associates
SWELL —CONSOLIDATION TEST RESULTS
Fig. 3
ICA
SAMPLE
LOCATION
BORING
1/68
DEPTH
(f
5
10
15
20
Kumar & Associates, Inc.
Geotechnical and Materials Engineers
and Environmental Scientists
kumarusa.com
NATURAL
MOISTURE
CONTENT
6.1
9.5
6.9
5.1
NATURAL
DRY
DENSITY
_ (Pcn
98
108
102
109
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
GRADATION
GRAVEL
(%)
SAND
(%)
ATTERBE
RG LIMRS
PLASTIC
INDEX
PERCENT
PASSING NO. LIQUID LIMIT
200 SIEVE
89
85
(%)
UNCONFINED
COMPRESSIVE
STRENGTH
(psf)
Project No. 19-7-221
Lot 68
SOIL TYPE
Sandy Silt and Clay
Sandy Clay
Sandy Clay
Sandy Clay
1