HomeMy WebLinkAboutSubsoil Study for Foundation Design 03.28.2022lcn f,tntn & lssociaics,lnc."
Geotechnical and Materials Engineers
and Envimnmental Scientisls
An Emdoycc Ormcd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusacom
www.kumarusa.com
Office tncations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit Cormty, Colorado
SUBSOIL STUDY
FOR T'OUNDATION DESIGN
PROPOSED RESIDENCE
LOT 3, MINEOTA ESTATES
MINEOTA DRIYE
GARX'.IELD COUNTY, COLORADO
PROJECT NO.22-7-121
MARCH 28,2022
PREPARED FOR:
JESUS H. SALINAS
P.O. BOX 1799
GLENWOOD SPRTNGS, COLOBADO 81601
salinas i esus23@smail.com
SITE CONDITIONS. ............ - I -
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
FIELD EXPLORATION
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS ..
DESIGN RECOMMENDATIONS
FOI-INDATIONS ...
FOUNDATION AND RETAINING WALLS
UNDERDRAIN SYSTEM
SURFACE DRAINAGE.....................
LIMITATIONS.
FIGURE 1 - LOCATION OF DGLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
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FLOOR SLABS
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5
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Kumar & Associates, lnc. o Projec{ No.22:I-121
PURPOSE AI\D SCOPE OF'STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot 3,
Mineota Estates, Mineota 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
Jesus H. Salinas, dated January 14,2022.
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, compressibility or
swell and other engineering characteristics. The results of the field exploration and laboratory
testing were analyzedto 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, recofitmendations and other geotechnical engineering
considerations based on the proposed construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
Design plans for the lot were in progress at the time of our study. The proposed building will be
single-story above crawlspace with a slab-on-grade garage,located as shown on Figure 1, and
cut into the north sloping terrain. Excavation for the building is expected to range between about
2 to 6 feet below the existing ground surface. For the pu{pose of our analysis, foundation
loadings for the structure were assumed to be relatively light and typical of the proposed type of
construction.
If building loadings, location or grading plans are significantly different from those described
above, we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The buildin g arcawas vacant and appeared mostly natural. The proposed residence site had been
staked and the snow of around one foot deep had been plowed along the driveway and in the
building area. The ground surface slopes gently to strongly down to the north at grades between
about 5 to |Yo through the driveway and building arca. Vegetation generally consisted of native
grass and weeds with scattered sage brush.
Kumar & Associates, lnc. @ Projec{ No.22-7-121
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FIELD EXPLORATION
The field exploration for the project was conducted on January 26,2022. Two exploratory
borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions.
The borings were advanced with 4-inch diameter continuous flight auger powered by a truck-
mounted CME-458 drill rig. The borings were logged by a representative of Kumar &
Associates, Inc.
Samples of the subsoils were taken with a 2-inchl.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-l586. 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 Logs of Exploratory Borings, Figure 2. The samples were returned to our
laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface profiles encountered at the site are shown on Figwe 2. Below
about I foot of topsoil, the subsoils consist of very stiff to hard, silty sandy clay to clayey sand
with scattered gravel. Clay soils like those encountered in the borings can possess an expansion
potential when wetted.
Laboratory testing performed on samples obtained during the field exploration included natural
moisture content and density and finer than sand size gradation analyses. Swell-consolidation
testing performed on relatively undisturbed drive samples of the clay soils, presented on
Figure 4,indicate low compressibility under relatively light surcharge loading and moderate to
high expansion potential when wetted under a constant light surcharge. The laboratory testing is
summarized in Table l.
No free water was encountered in the borings at time of drilling and the subsoils were slightly
moist.
FOT]NDATION BEARING CONDITIONS
The clay soils encountered at the site possess an expansion potential when wetted under light
loading. Shallow foundations placed on the expansive soils similar to those encountered at this
site can experience movement causing structural distress if the clay is subjected to changes in
moisture content. Surface runoff, landscape irrigation, and utility leakage are possible sources of
water which could cause wetting. Footings placed on a minimum 3 feet of compacted structural
fill such as road base could be used to reduce but not eliminate the risk of movement and
Kumar & Associates, lnc. o Proiect No.22-7-121
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building distress. A lower movement risk foundation would be to support the foundation with
piers or piles which penetrate the expansive materials and place the bottom of the piers in azotte
of relatively stable moisture conditions at around 25 feet or greater depth. Presented below are
recommendations for footings placed on compacted structural fill. If a deep foundation is
desired, we should be contacted for additional recommendations.
DESIGN RECOMMENDATIONS
FOIINDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, the building can be founded with spread footings placed on
compacted structural fi li.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1)Footingsplacedonatleast3feetof"@lshouldbedesigned
for an allowable bearing pressure o?000 pt The fill should extend laterally out
from the edge of the footing at least lYzfeet on both sides. Structural filIused
below the foundation should be a relatively well graded granular material such as
CDOT Class 6 road base compacted to at least 98oh of standard Proctor density.
2) 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 of around I inch depending on the depth the bearing soils
are wetted.
3) The footings should have a minimum width of 16 inches for continuous footings
and24 inches for isolated Pads'
4) Continuous foundation walls should be heavily reinforced top and bottom to span
local anomalies and limit the risk of differential movement. One method of
analysis is to design the foundation wall to span an unsupported length of at least
12 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.
5) 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.
6) Prior to the footing construction, the topsoil, required clay sub-excavation depth
and loose or disturbed soils should be removed from footing areas. The exposed
soils should then be moistened and compacted prior to placing structural fill.
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A representative of the geotechnical engineer should evaluate compaction of
structural fill on a regular basis and observe all footing excavations prior to
concrete placement for 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 60 pcf for backfill consisting
of the on-site fine-grained soils and at least 45 pcf for backfill consisting of imported granular
materials. Cantilevered retaining structures which are separate from the buildings 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 50 pcf for backfill consisting of the on-site fine-grained soils and at least 40 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
backfrll 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 near optimum moisture content. Backfill placed in pavement areas
should be compacted to at leastglYo 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
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 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
7)
Kumar & Associates, lnc. @ Projed No.22-7-121
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the sides of the footings to resist lateral loads should be compacted to at least 95% of the
maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The on-site soils possess an expansion potential and slab heave could occur if the subgrade soils
were to become wet, similar to that in footing areas. Slab-on-grade construction can be used in
less movement sensitive slabs, such as the garage, 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 are4 is to construct
structurally supported floors over crawlspace and is recommended for living areas of the
residence. Where slab-on-grade is used, we recommend at least 2 feet of relatively well graded
granular material such as CDOT Class 6 road base be placed below floor slabs to help mitigate
the expansion potential.
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 1%-inches of vertical movement are
recommended. Floor slab control joints should be used to reduce damage due to shrinkage
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 relatively well graded sand and gravel such as road base should be
placed immediately beneath interior slabs-on-grade. This material should consist of minus
2-inch aggregate with less than 50% passing the No. 4 sieve and less than l2oh passing the
No. 200 sieve. Required fill beneath slabs should consist of a suitable imported granular
material, excluding topsoil and oversized rocks. The fill should be spread in thin horizontal lifts,
adjusted to at or above optimum moisture content, and compacted to at least95Yo of the
maximum standard Proctor density. All vegetation, topsoil and loose or disturbed soil should be
removed prior to filIplacement.
The above recommendations will not prevent slab heave if the expansive soils underlying slabs-
on-grade become wet. However, the recoflrmendations will reduce the effects if slab heave
occurs. All plumbing lines should be pressure tested before backfilling to help reduce the
potential for wetting.
Kumar & Associates, lnc, o Proiect No.22-7-121
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TINDERDRAIN SYSTEM
Although groundwater was not encountered during our exploration, it has been our experience in
the area and where clay soils are present that local perched groundwater can develop during
times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a
perched condition. Therefore, we recommend below-grade construction, such as deep
crawlspace areas, be protected from wetting by an underdrain system. The drain should also act
to prevent buildup of hydrostatic pressures behind foundation walls. Crawlspaces less than
4 feet and the slab-on-grade garage areas should not require an underdrain with proper surface
grading and drainage as recommended below.
The underdrain system should consist of a drainpipe surrounded by free-draining granular
material placed at the bottom of the wall backfill. The drain lines should be placed at each level
of excavation and at least I foot below lowest adjacent finish grade, and sloped at a minimum
lVo grade to a suitable gravity outlet. Free-draining granular material used in the drain system
should consist of minus 2-inchaggregate with less than50Yo passing the No. 4 sieve and less
than2Yo passing the No. 200 sieve. The drain gravel should be at least lYz feet deep.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the building has been completed:
1) Excessive wetting or drying of the foundation excavations and underslab areas
should be avoided during construction. Drying could increase the expansion
potential of the clay soils.
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 areas and to at
least 90% of the maximum standard Proctor density in landscape 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.
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 l0 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 inigation.
Kumar & Associates, Inc. @ Project No.22-7-121
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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 zubmitted inthis report are based uponthe data obtained
from the exploratory borings drilled at the locations indicated on Figure l, the proposed type of
construction and our experience in the area. Our services do not include deterrrining the
presenoe, prevention or possibility of mold or other biological contaminants (MOBC) developing
in the future. If the client is concemed about MOBC, then a professional in this special field of
ptastice should be consulted. Our findings include interpolation and extrapolation of the
subsurface conditions idbntified 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
shouldprovide continued consultation and field services during constructionto review and
monitor the imptementation 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 presenfed 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 Submitte4
Kumar & Associates, Inc.
Steven L. Pawlak"
Reviewed by:
O !
Daniel E. Hardin, P.E.
SLP/kac
Cc: J. Catib€r Constnrction - Jose Ganzalez(jose(@jcaliberconstruction.com)
Kumar & Associates, lnc.to Project No.22-7-121
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22-7 -121 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
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BORING 1
EL. 5624'
BORING 2
EL. 5628'
0 0
32/12
WC=4.8
DD=1 1 7
34/ 12
WC=6.5
DD=116
-2QO=75
5 5
57 /12 35/12
10 34/12
WC=8.5
DD= 1 20
10
38/12
WC=7.3
DD= 1 08
-200=95
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82/12 30/12
WC=5.4
DD=1 18
20 20
83/12
WC=4.8
DD= 1 29
-2OO=51
35/12
25 25
50 3030/6, 5O/5
22-7 -121 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, BROWN.
CLAY AND SAND (CL-SC); SILTY, SCATTERED GRAVEL, VERY STIFF TO HARD,
SLIGHTLY MOIST, LIGHT BROWN, CALCAREOUS AND POROUS TRACES, LOW
PLASTICITY.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE
32/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 52 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 JANUARY 26, 2022 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 PI.AN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
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);
DD = DRY DENSITY (PCt) (ASTM D2216);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM Dl140).
22-7 -121 Kumar & Associates LEGEND AND NOTES Fig. 3
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SAMPLE OF: Very Sondy Silty Cloy
FROM:Boringl@2.5'
WC = 4.8 %, DD = 117 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
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PRESSURE _ KSF l0 100
SAMPLE OF: Very Sondy Silly Cloy
FROM: Boring2fJ- 1O'
WC = 8.5 %, DD = 120 pcf
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EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
22-7-121 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
l(+AHrffi[*Tfffin'$:'i*'"
TABLE 1
SUIJIMARY OF LABORATORY TEST RESULTS
No.22-7-12'l
Very Sandy Silty Clay with
Gravel
Very Sandy Silty Clay
Slightly Sandy Silty Clay
Very Sandy Silty Clay with
Gravel
Sandy Silty Clay
Very Sandy Silty Clay
SOIL TYPE
(psfl
UNCONFINED
COMPRESST\IE
STRENGTH
iLIMITS
PLASTIC
INDEX
{o/.)
ATTERBEf
(o/ol
LIQUID LIMIT
75
93
15
PERCENT
PASSING NO.
200 slE\rE(:/"1
SAND
GRADATION
(/"1
GRAVEL
118
108
t29
tt6
r20
(pcfl
NATURAL
DRY
DENSITY
rt7
6.3
8.5
5.4
4.8
7.3
4.8
lo/ol
NATURAL
MOISTURE
CONTENT
2%
01
51
(ft)
DEPTH
2%
10
20
2
SAMPLE LOCATION
BORING
1