HomeMy WebLinkAboutSoils Report 06.03.2019K+A
1Y
Kumar & Associates, Ina.
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
RECEIVED
JUL 0 9 2019
GARFIELD COUNTY
COMMUNITY DEVELOPMENT
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE AND BARN
TRACT 9, ANTLERS ORCHARD
TBD COUNTY ROAD 237
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-303
JUNE 3, 2019
PREPARED FOR:
IAN & KRISTIN BYMAN
361 WEST ORCHARD AVENUE
SILT, COLORADO 81652
Ian t luxelectrie.coni
krit07,tr: hotmail.com
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TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 2 -
GEOLOGY -2-
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 3 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 4 -
FOUNDATIONS - 4 -
FOUNDATION AND RETAINING WALLS - 5 -
FLOOR SLABS -6-
SITE GRADING -7 -
SURFACE DRAINAGE - 7 -
LIMITATIONS - 8 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURES 4 & 5 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. 0 Project No. 19-7-303
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence and barn to be located
on Tract 9, Antlers Orchard, TBD County Road 237 in 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 proposal for geotechnical
engineering services to Ian & Kristin Byman, dated May 9, 2019.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils and bedrock 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, recommendations
and other geotechnical engineering considerations based on the proposed construction and the
subsurface conditions encountered.
PROPOSED CONSTRUCTION
At the time of our study, design plans for the residence and barn were preliminary. The
proposed house, detached garage, and barn locations are shown on Figure 1. You have indicated
that the house will be a two-story wood frame structure with a slab -on -grade main floor. The
detached barn will be 40 feet by 60 feet also with slab -on -grade floor. Below grade construction
is not currently planned. We assume excavation for the buildings will have a maximum cut
depth of about 3 to 6 feet below the existing ground surface. For the purpose of our analysis,
foundation loadings for the structures were assumed to be relatively light and typical of the
proposed type of construction.
When grading and loading information have been developed, or if the proposed construction
differs than described above, we should be notified to re-evaluate the recommendations
presented in this report.
Kumar & Associates, Inc. Project No. 19-7-303
2
SITE CONDITIONS
The lot was vacant at the time of our field exploration. A waterline easement crosses between
the building site as shown on Figure 1. The ground surface is moderately sloping down to the
east at about 10% grade and is steeply sloping near the southwest corner of the lot. An
ephemeral drainage cuts through the lot from the northwest to the southeast corners. Vacant land
is north and south, single family residences are east and west, and Country Road 237 is east of
the site.
GEOLOGY
According to the Geologic Map of the Leadville 1 °x 2° Quadrangle, Northwestern Colorado,
dated 1978, by Tweto, Ogden, Moench, R.H., and Reed, J.C., the site is underlain by the
Wasatch and Ohio Creek Formations. These formations are described as variegated claystone,
siltstone, sandstone, and conglomerate with carbonaceous shale and lignite near its base.
Sandstone outcrops were observed near the site.
FIELD EXPLORATION
The field exploration for the project was conducted on May 20, 2019. 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 auger powered by a truck-
mounted CME -45B drill rig. The borings were logged by a representative of Kumar &
Associates.
Samples of the subsoils were taken with 1% inch and 2 inch I.D. spoon samplers. The samplers
were 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 and hardness of the bedrock. Depths at which the samples were taken and the
penetration resistance values are shown on the Logs of Exploratory Borings, Figure 2. The
samples were returned to our laboratory for review by the project engineer and testing.
Kumar & Associates, Inc. Project No. 19-7-303
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SUBSURFACE CONDITIONS
Graphic logs of the subsurface profiles encountered at the site are shown on Figure 2. Below
about 'A foot of organic topsoil and 7 feet of stiff to very stiff, sandy silt and clay in Boring 2, the
subsoils consist of 7 to 16.5 feet of medium dense/very stiff, silty sand and clay with gravel,
underlain by dense, silty, clayey sand and gravel in Boring 1. Weathered claystone bedrock was
encountered in Boring 2 at about 14 feet below ground surface. The clay portions of these soils
can possess an expansion potential when wetted.
Laboratory testing performed on samples obtained during the field exploration included natural
moisture content and density and percent fines (finer than the No. 200 sieve). Swell -
consolidation testing was performed on relatively undisturbed drive samples of the clay subsoils.
The swell -consolidation test results, presented on Figures 4 and 5, indicate low compressibility
under relatively light surcharge loading and natural low moisture content. The upper soils
showed nil to low expansion potential when wetted under a constant light surcharge and the
deeper clay soils showed moderate expansion potential when wetted. Undisturbed sampling of
the clayey gravel soils was not possible due to the rock content. The laboratory testing is
summarized in Table 1.
No free water was encountered in the borings at time of drilling. The subsoils were slightly
moist to moist.
FOUNDATION BEARING CONDITIONS
The clay soils encountered at the site appear to typically possess expansion potential when
wetted. Shallow spread footings appear feasible for foundation support of the residence with a
risk of differential movement and building distress. To reduce the risk of movement, spread
footings could bear on a minimum 3 feet of compacted structural fill.
It may be feasible to not
sub -excavate and replace the natural soils with structural fill which should be further evaluated at
the time of construction. Precautions should be taken to prevent wetting of natural bearing soils
below the footings. Sources of wetting include excessive irrigation near the foundation, poor
surface drainage adjacent to foundation walls and utility line leaks.
Kumar & Associates, Inc. Project No. 19-7.303
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A lower movement risk foundation system is a deep foundation, such as drilled picrs or
mieropiles, bearing in the natural sand and gravel soils or bedrock below an assumed wetted
depth (typically about 15 to 20 feet).
Provided below are recommendations for spread footings bearing on compacted structural fill or
the natural soils. If recommendations for a deep foundation are desired, we should be contacted.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, the building can be founded with spread footings bearing on a
minimum 3 feet of compacted structural fill or on natural non -expansive soils with a risk of
movement. The structural fill should consist of non -expansive soil compacted to a minimum of
95% of the standard Proctor density.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1)
Footings placed on a minimum 3 feet of compacted structural fill or on the natural
non -expansive soils can be designed for an allowable bearing pressure of 2,000
psf. Based on experience, we expect initial settlement of footings designed and
constructed as discussed in this section will be up to about 1 inch. There could be
additional movement if the bearing soils were to become wet. The magnitude of
the additional movement would depend on the depth and extent of the wetting but
may be on the order of1/2 to 1 inch.
2) The footings should have a minimum width of 16 inches for continuous footings
and 24 inches for isolated pads.
3) Continuous foundation walls should be heavily reinforced top and bottom to span
local anomalies and limit the risk of differential movement. Onc mncthod of
analysis is to design the foundation wall to span an unsupported length of at least
14 feet. Foundation walls acting as retaining structures should also be designed to
resist a lateral earth pressure as discussed in the "Foundation and Retaining
Walls" section of this report.
Kumar & Associates, Inc. Project No. 19.7.303
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4) 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 the exterior grade is typically used in this
area.
5) Prior to the footing construction, any existing fill, topsoil and loose or disturbed
soils should be removed and the footing bearing level extended down to
competent baring soils. We should evaluate the exposed soils for expansion
potential prior to placing footing forms.
6) A representative of the geotechnical engineer should observe all footing
excavations and test structural fill for compaction during its placement 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 55 pcf for backfill consisting
of the on-site soils and at least 45 pcf for backfill consisting of imported granular materials.
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 soils and at least 35 pcf for backfill consisting of imported
granular materials.
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. Care should be taken not to
Kumar & Associates, Inc. Project No. 19-7-303
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ovcrcompact thc backfill or use large equipment ncar thc 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
based on a coefficient of friction of 0.40. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 300 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 compacted to at least 95% of the maximum
standard Proctor density at a moisture content near optimum.
FLOOR SLABS
Some of the on-site soils possess an expansion potential and slab heave could occur if the
subgradc soils were to become wet. The expansion potential should be further evaluated at the
time of excavation. Slab -on -grade construction may be used provided precautions are taken to
limit potential movement and the risk of distress to the building is accepted by the owner. A
positive way to reduce the risk of slab movement, which is commonly used in the area, is to
construct structurally supported floors over crawlspace.
To reduce the effects of some differential movement, nonstructural floor slabs should be
separated from all bearing walls and columns with expansion joints which allow unrestrained
vertical movement. Interior non-bearing partitions resting on floor slabs should be provided with
a slip joint at the bottom of the wall so that, if the slab moves, the movement cannot be
transmitted to the upper structure. This detail is also important for wallboards, stairways and
door frames.
Slip joints which will allow at least 11/2 inches of vertical movement are
recommended.
Floor slab control joints should be used to reduce damage due to shrinkage
Kumar & Associates, Inc. Project No. 19-7-303
-7 -
cracking. Slab reinforcement and control joints 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 immediately beneath basement
level slabs -on -grade. 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.
All fill should be spread in thin horizontal lifts, adjusted to at or above optimum moisture
content, and compacted to at least 95% of the maximum standard Proctor density. All
vegetation, topsoil and loose or disturbed soil should be removed prior to fill placement.
The above recommendations will not prevent slab heave if the expansive soils underlying slabs -
on -grade become wet. However, the recommendations will reduce the effects if slab heave
occurs. All plumbing lines should be pressure tested before backfilling to help reduce the
potential for wetting.
SITE GRADING
The risk of construction -induced slope instability at the site appears low. We assume the cut
depth for the foundations will not exceed 3 to 5 feet. Embankment fills should be compacted to
at least 95% of the maximum standard Proctor density near optimum moisture content. Prior to
fill placement, the subgrade should be carefully prepared by removing all vegetation and topsoil
and compacting to at least 95% of the maximum standard Proctor density. The fill should be
benched into slopes that exceed 20% grade. Permanent unretained cut and fill slopes should be
graded at 2 horizontal to 1 vertical or flatter and protected against erosion by revegetation or
other means. This office should review site grading plans for the project prior to construction.
SURFACE DRAINAGE
Providing proper surface grading and drainage will be critical to limiting subsurface wetting and
potential movement of the structures. The following drainage precautions should be observed
during construction and maintained at all times after each structure has been completed:
1) Excessive wetting or drying of the foundation excavations and underslab areas
should be avoided during construction.
Kumar & Associates, Inc. Project No. 19-7-303
8
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95% of the maximum standard Proctor density in pavement arcas 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.
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 borings drilled at the locations 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 borings 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
monitor the implementation of our recommendations, and to verify that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
Kumar & Associates, Inc. Project No. 19-7-303
9 -
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.
Respectfully Submitted,
Kumar & Associates, Inc.
i444c
Shane J. Robat, P.E.
Project Manager
Reviewed by:
Steven L. Pawlak,
SJR/kac
Kumar & Associates, Inc. Project No. 19-7-303
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HOUSE SITE
BORING 1
EL. 100'
26/12
WC=6.4
DD=110
18/12
WC=5.0
DD=98
- 200=40
23/12
23/12
WC=7.6
DD=124
- 200=49
27/6, 50/4
BARN SITE
BORING 2
EL. 103.5'
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WC=5.9
DD=98
-200=79
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WC=4.2
DD=106
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WC=5.5
DD=122
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19-7-303
Kumar & Associates
LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
TOPSOIL; SANDY, SILTY, CLAY, ORGANIC, FIRM, MOIST, DARK BROWN.
' SAND AND CLAY (SC -CL); SILTY WITH GRAVEL, MEDIUM DENSE/VERY STIFF, SLIGHTLY MOIST
/ TO MOIST, BROWN.
® SILT AND CLAY (ML—CL); SANDY, STIFF TO VERY STIFF, SLIGHTLY MOIST, BROWN.
GRAVEL AND SAND (GM—SM, GG—SC); SILTY, CLAYEY, DENSE, MOIST, MIXED BROWN.
•
WEATHERED CLAYSTONE; HARD, SLIGHTLY MOIST, GRAY, PURPLE & RUST. WASATCH
FORMATION.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST.
26/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 26 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON MAY 20, 2019 WITH A 4—INCH—DIAMETER
CONTINUOUS—FLIGHT POWER AUGER.
2. THE EXPLORATORY BORINGS WERE LOCATED BY THE CLIENT.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER
TO BORING 1 AS ELEVATION 100', ASSUMED,
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 DRII LING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM 02216);
DD = DRY DENSITY (pcf) (ASTM D2216);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM 01140).
19-7-303
Kumar & Associates
LEGEND AND NOTES
Fig. 3
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CONSOLIDATION - SWELL
— 3
— 4
0
—1
-- 2
—3
SAMPLE OF: Very Sandy Clay
FROM: Boring 1 0 2.5'
WC = 6.4 %, DD = 110 pcf
T
1
I� EXPANSION UNDER CONSTANT
3r jr PRESSURE UPON WETTING
F�
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I.0 APPLIED PRESSURE — KSF 10
100
SAMPLE OF: Silty Sandy Clay
FROM: Boring 2 c 5'
WC = 4.2 %, DD = 106 pcf
AD- DITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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1.0 APPLIED PRESSURE — KSF
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10 100
SWELL—CONSOLIDATION TEST RESULTS
Fig. 4
CONSOLIDATION - SWELL
3
2
1
0
—1
— 2
— 3
— 4
SAMPLE OF: Sandy Clay with Gravel
FROM: -Boring 2 ® 10'
WC = 5.5 %, DD = 122 pcf
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EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
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19-7-303
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 5
K+A
Kumar & Associates, Inc. ®
Geotechnical and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Protect No.19-7-303
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(Pci)
GRADATION
PERCENT
PASSING
200 VE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(psf)
SOIL TYPE
BORING
DEPTH
(ft)
GRAVEL
(%)
SAND
()
LIQUID LIMB
(%)
PLASTIC
INDEX
f^)
1
2Y2
6.4
110
Very Sandy Clay
5
5.0
98
40
Silty Clayey Sand with
Gravel
15
7.6
124
49
Very Clayey Sand with
Gravel
2
21/2
5.9
98
79
Silty Sandy Clay
5
4.2
106
Silty Sandy Clay
10
5.5
122
Sandy Clay with Gravel
1
1
1