HomeMy WebLinkAboutSoils Report 01.02.2020KFA
Kumar & A.asocla[es, Inc.
GeolecFlnical and Materials Engineers
and l~nvironmental.Scianlis1s
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 Sumrnil County, Colorado
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SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 10, SUN MEADOW ESTATES
329 COUNTY ROAD 216
(ANTONELLI LANE)
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-709
JANUARY 2, 2020
PREPARED FOR:
COLONNA CONSTRUCTION
ATTN: BERNIE COLONNA
P.O. BOX 1968
RIFLE, COLORADO 81650
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TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1 -
GEOLOGY -2-
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 2 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FLOOR SLABS - 4 -
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. 0 Project No. 19.7-709
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot 10, Sun Meadow Estates, 329 County Road 216 (Antonelli Lane), 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 Colonna Construction dated December 2,
2019.
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-story structure with an attached 3 car garage and located at
the exploratory boring shown on Figure 1. Ground floor for the residence and garage will be
structural floor over crawlspace and slab -on -grade, respectively. Grading for the structure is
assumed to be relatively minor with cut depths between about 3 to 4 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 site was mostly vacant with a small shed near the middle of the lot at the time of our field
exploration. The existing house on the southern portion of the lot had been demolished prior to
Kumar & Associates, Inc. ® Project No. 19.7-709
2
our arrival. The ground surface is relatively flat with a gentle slope down to the east and west
and is vegetated with grass and weeds. A community well is to the east of the proposed
residence, single-family residences are generally in each direction, and Antonelli Lane (CR 216)
and South Meadow Drive are to the south.
GEOLOGY
According to the Geologic Map of the Silt Quadrangle, Garfield County, Colorado, by Ralph R.
Shroba and Robert B. Scott, dated 2001, the site is underlain by loess over older terrace
alluvium. Loess is described as wind -deposited, nonstratified, calcareous, slightly clayey, sandy
silt, that is friable when dry and slightly plastic when wet. Older terrace alluvium is described as
stream alluvium that underlies terrace remnants about 35-50 meters above the Colorado River,
Mamm Creek, and Dry Hollow Creek.
FIELD EXPLORATION
The field exploration for the project was conducted on December 26, 2019. 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.
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 encountered, below about 1/2 foot of topsoil, consist of about 71/2 feet of stiff to very stiff,
sandy silt, underlain by about 71/2 feet of very stiff, silty sandy clay, underlain by medium dense
to dense clayey silty sand and gravel.
Kumar & Associates, Inc. Project No. 19-7-709
-3
Laboratory testing performed on samples obtained from the boring included natural moisture
content and density and finer than sand size gradation analyses. Results of swell -consolidation
testing performed on relatively undisturbed drive samples, presented on Figure 3, indicate low
compressibility under loading and slight collapse or expansion potential upon wetting 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 the subsoils were slightly
moist to moist with depth.
FOUNDATION BEARING CONDITIONS
The upper silt and clay soils showed a slight collapse potential and the underlying clay soils a
slight expansion potential. Spread footings or a frost protected structural slab with thickened
edges bearing on the natural silty and clay soils appear feasible for foundation support with a risk
of movement and distress. The risk of movement is primarily if the bearing soils were to become
wetted and precautions should be taken to prevent wetting. Removal and replacement of a depth
of the natural soils (typically 3 to 4 feet) in a moistened and compacted condition below the
footings could be done to reduce the risk of foundation movement and building distress. The
collapse or expansion potential of the subgrade soils should be further evaluated for possible
mitigation measures at the time of excavation.
Use of a relatively deep foundation system, such as drilled piers or helical piers, that extend
down into less compressible granular soils would provide a relatively low risk of foundation
movement. Provided below are recommendations for spread footings bearing on the natural
soils. If recommendations for spread footings bearing on a depth of compacted structural fill,
drilled piers or helical piers are desired, we should be contacted.
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 or a frost protected
structural slab with thickened edges bearing on the natural silt and clay soils with a risk of
movement and distress.
Kumar & Associates, Inc. s Project No. 19.7-709
4
The design and construction criteria presented below should be observed for a spread footing or
structural slab foundation system.
1) Footings placed on the undisturbed natural silt and clay soils 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
will be about 1 inch or less. The magnitude of the additional movement would
depend on the depth and extent of the wetting but may be on the order of 1 to
1'/2 inches.
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
unless protected against frost by insulation extending down and out from the
perimeter of the heated structure.
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 12 feet.
Foundation walls acting as retaining structures (if any) should also be designed to
resist lateral earth pressures of at least 55 pcf equivalent fluid unit weight.
5) The topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the firm natural soils. The exposed soils in
footing area should then be moistened and compacted.
6) A representative of the geotechnical engineer should 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 and distress mainly if the bearing soils are wetted. To
reduce the effects of some differential movement, non-structural 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.
Kumar & Associates, Inc. Project No. 19.7-709
Proper surface grading and drainage will be critical to keeping the bearing soils dry and limiting
-5 -
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 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 soils devoid of vegetation and topsoil or imported granular soils such as road base.
SURFACE DRAINAGE
building movement and distress.
The following drainage precautions should be observed during
construction and maintained at all times after the boring 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 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.
Kumar & Associates, Inc. Project No. 19.7.709
6
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 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.
<cit4w-ide-----
Shane J. Robat, P.E.
Reviewed by:
Steven L. Pawlak,
SJR/kac
Kumar & Associates, Inc.
Project No. 19-7-709
LOT 4 / 1 LOT 5 i LOT 6
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1 ; 1
1 1
1 {!1 LOT 8
I 1
1
t 1 BORING 1
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1 1
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LOT 11
1
LOT 10
CR 216 (ANTONELLI LANE)
SOUTH MEADOW DR.
50 0 50 100
APPROXIMATE SCALE -FEET
LOT 9
19-7-709
Kumar & Associates
LOCATION OF EXPLORATORY BORING
Fig. 1
uJ
w
La
x
F-
0
w
0
— 0
5
10
15
— 20
— 25
BORING 1
21/12 21/12
WC=5.1
DD=97
— 200=75
13/12
WC=4.4
DD=98
28/12
WC=16.9
DD=111
24/12
41/12
WC=7.8
DD=132
— 200=27
42/12
LEGEND
TOPSOIL; SANDY SILT, ORGANIC, FIRM, MOIST, DARK BROWN.
�L.
—7
9
SILT (ML); SANDY, STIFF TO VERY STIFF, SLIGHTLY MOIST, LIGHT
BROWN.
CLAY (CL); SILTY, SANDY, VERY STIFF, MOIST, BROWN.
SAND AND GRAVEL (SC—GC); CLAYEY, SILTY, MEDIUM DENSE TO
DENSE, MOIST, BROWN.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
21/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 21 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 DECEMBER 26,
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 NOT
MEASURED AND THE LOG OF THE EXPLORATORY BORING IS
PLOTTED TO DEPTH.
4. THE EXPLORATORY BORING LOCATION 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
- 30 TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pci) (ASTM D 2216);
—200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
19-7-709
Kumar & Associates
LOG OF EXPLORATORY BORING
Fig. 2
6
CONSOLIDATION - SWELL
CONSOLIDATION - SWELL
1
0
—1
— 2
— 3
— 4
1
0
— 1
— 2
— 3
SAMPLE OF: Sandy Silt
FROM: Boring 1 ® 5'
WC = 4.4 %, DD = 98 pcf
6
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPLIED PRESSURE — l<SF In 100
SAMPLE OF: Sandy Silty Clay
FROM: Boring 1 CO 10'
WC = 16.9 %, DD = 111 pcf
EXPANSION UNDER CONSTANT
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1.0 APPLIED PRESSURE — KSF 10
PRESSURE UPON WETTING
100
19-7-709
Kumar & Associates
SWELL -CONSOLIDATION TEST RESULTS
Fig. 3
Kumar & Associates, Inca
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 19.7-709
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
1 (PSD _
GRADATION
PERCENT
P200 SIEVNO. E
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(psf)
SOIL TYPE
BORING
DEPTH
(ft)
GRAVEL
(%)
SAND
(%)
LIQUID LIMIT
(%)
PLASTIC
INDEX
[%)
1
2'/2
5.1
97
75
Sandy Silt
5
4.4
98
Sandy Silt
10
16.9
111
Sandy Silty Clay
20
7.8
132
27
Silty Clayey Sand and
Gravel