HomeMy WebLinkAboutSubsoils Report for Foundation DesignI(tAflffilfi#x:ffiniiyi*'"
An Employcc Orncd Compony
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
F'OR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 30, FOUR MrLE RANCH
143 MAROON DRIVE
GARFIELD COUNTY, COLORADO
PROJECT NO.23-7-2s9
JUNE 20,2023
PREPARED F'OR:
RICHARD KOZIOL
2102 GRAND AVENUE
GLENWOOD SPRTNGS, COLORADO 81601
richvkoziol@em ail. com
TABLE OF'CONTENTS
PROPOSED CONSTRUCTION 1
SITE CONDITIONS -t -
FIELD EXPLORATION
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS
FOUNDATIONS
FOUNDATION AND RETAINING WALLS
LINDERDRAIN SYSTEM
SURFACE DRAINAGE.....................
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURES 4 and 5 - SWELL-CONSOLIDATION TEST RESULTS
FIGURE 6 - GRADATION TEST RESULTS
TABLE I- SUMMARY OF LABORATORY TEST RESULTS
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1
2
.'
...........-2 -
.....- 3 -
FLOOR SLABS ....- 4 -
-5-
-5-
-6-
Kumar & Associates, lnc. o Project No. 23.7-259
PURPOSE AND SCOPE OF' STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on
Lot 30, Four Mile Ranch, 143 Maroon Drive, 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 Richard Koziol, dated April 2I,2023.
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 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 is assumed to be a one- or two-story wood frame structure over a
walkout basement. Ground floor will be slab-on-grade. Grading for the structure is assumed to
be relatively minor with cut depths between about 3 to 10 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 desuibed above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The site was vacant at the time of our subsoil study and the building envelope was staked. The
lot slopes moderately down to the west through the building envelope, with a strong slope down
to Maroon Drive that borders the lot on the west side. A utility easement and access road borders
the lot to the north. Vegetation consists of sage brush and grasses, and scattered basalt cobbles
and small boulders are visible on the ground surface.
FIELD EXPLORATION
The field exploration for the project was conducted on May 8, 2023. 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 augers powered by a truck-
Kumar & Associates, lnc. @ Project No. 23-7-259
.,
mounted CME-458 drill rig. The borings were logged by a representative of Kumar &
Associates, Inc.
Samples of the subsoils were taken with l% 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. 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 conditions encountered at the site are shown on Figure 2. The
subsoils, below about Yz foot of topsoil, consist of about 3% feet in Boring I and 12% feet in
Boring 2 of sandy clay overlying silty clayey sand that extended down to 2l feetand 3l feet,
respectively, the maximum depth explored.
Laboratory testing performed on samples obtained from the borings included natural moisture
content, density and gradation analyses. Results of swell-consolidation testing performed on
relatively undisturbed drive samples of the shallow stiff clay soils, presented on Figures 4 and 5,
indicatd low compressibility undei light loading and a low to'moderate compressibility when
wetted and loaded. The laboratory testing is summarized in Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were moist
to slightly moist with depth.
FOUNDATION BEARING CONDITIONS
Foundations should bear on the relatively dense clayey sand soils encountered in the borings at
depths of 4 to 13 feet. The topsoil and clay soils should be removed from below all footing
areas. If needed, imported structural fill such as %-inch road base can be placed below footing
areas to re-establish design grades.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded with spread lootings bearing
on the natural granular soils.
Kumar & Associates, lnc. @ Project No. 23-7-259
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The design and construction criteria presented below should be observed for a spread footing
foundation system.
l) Footings placed on the undisturbed natural granular soils or compacted structural
fill should be designed for an allowable bearing pressurryfllQ!(lqg[ Based on
experience, we expect settlement of footings designed and constructed as
discussed in this section will be about 1 inch or less.
2) The footings should have a minimum width of 16 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. G
4) Continuous foundation walls should be 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 should also be designed to resist
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this report.
5) All existing fill, topsoil, clay soils and any loose or disturbed soils should be
removed and the footing bearing level extended down to the relatively dense
natural granular soils. The exposed soils in footing areas should then be
moistened and compacted. If water seepage is encountered, the footing areas
should be dewatered before concrete placement. If needed, structural fill
consisting of 3/+-inchroad base can be placed and compacted in thin lifts to at least
98% of the maximum standard Proctor density at a moisture content near
optimum to re-establish design footing grades.
6) A representative ofthe geotechnical engineer should observe all footing
excavations and test structural fill prior to concrete placement to evaluate bearing
conditions.
FOLINDATION 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 50 pcf for backfill consisting
of the on-site 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 40 pcf for backfill consisting of the on-site soils'
Kumar & Associates, lnc. @ Project No. 23-7-259
-4-
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 surfaoe. 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%o of the maximum
standard Proctor density at a moisture content near optimum. Backfill in pavement and walkway
areas should be compacted to at least95Yo 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. Backfill should not contain organics, debris or rock larger
than about 6 inches.
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 coefficienl. of friction of 0.30. Passive pressure of compacted backfill against the
sides of the iootings 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
the sides of the footings to resist lateral loads should be a granular material compacted to at least
95Yo 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. 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 free-
draining gravel should be placed beneath basement level slabs for support and to facilitate
drainage. This material should consist of minus 2-inch aggregate with at least 50% retained on
the No. 4 sieve and less than2oh passing the No. 200 sieve.
Kumar & Associates, Inc. @ Project No. 23-7-259
5
All fill materials for support of floor slabs should be compacted to at least95o/o 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
Although free water was not encountered during our exploration, it has been our experience in
mountainous areas 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. We recommend below-grade construction, such as retaining walls,
crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by
an underdrain system.
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 TYoto
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2%o passingthe No. 200 sieve, less than 50%o passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least l% feet deep and covered
with filter fabric such as Mirafi 140N.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
1) Inundation ofthe foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
atleastg5%o 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
5 feet from foundation walls.
Kumar & Associates, lnc. o Project No. 23-7-259
-6-
LIMITATIONS
This study has been conducted in aicordance 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 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 veriry 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 skata and testing of structural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
Kumar & Associates, Inc.
\Jd-
David A. Noteboom, Staff Engineer
Reviewed by:
Robert L.
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BORING 2
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23-7 -259 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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LEGEND
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TOPSOIL; ORGANIC SANDY SILT & CLAY' FIRM' MOIST' BROWN
CLAY (CL); SANDY, SILTY, STIFF TO VERY STIFF, MOIST TO SLIGHTLY MOIST, BROWN'
SLIGHTLY TO MODERATELY CALCAREOUS.
SAND (sc);
TO DENSE,
CLAYEY TO SLIGHTTY CLAYEY, SILTY, WITH SCATTERED GRAVEL, MEDIUM DENSE
MOIST TO SLIGHTLY MOIST, BROWN.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE
,^,.^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 32 BLOWS OF A 14o-POUND HAMMERrz/ tz FALLING SO TNCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON MAY 8, 2023 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 PLAN 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) (ISTU D2216);
_2OO = PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D1140).
23-7 -259 Kumar & Associates LEGEND AND NOTES Fig. 3
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SAMPLE OF: Very Sondy Cloy
FROM:Boringl@2.5'
WC = 16.9 %, DD = 108 pcf
NO MOVEMENT UPON
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ADDITIONAL COMPRESSION
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23-7 -259 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 4
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SAMPLE OF: Very Sondy Cloy
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ADDITIONAL COMPRESSION
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23-7 -259 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5
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CLAY TO SILT COBBLES
GRAVEL O % SAND 62 %
LIQUID LIMIT - PLASTICITY INDEX
SAMPLE 0F: Very Cloyey Sond
SILT AND CLAY 3A%
FROM:BoringlO15'
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ASIM C136 ond/or ASTM 011,10.
HYDROMETER ANALYSIS SIEVE ANALYSIS
24 HRs / HHS45 HIN l5 VtN
TIMI REAOINCS
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U.S. STAilDARO SERIES CLEAR SOUARE OPENINGS
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FIN E MEDIUM COARSE FINE COARSE
23-7 -259 Kumar & Associates GRADATION TEST RESULTS Fig.6
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
ATI LtilTSG{SAIIPLE LOCAIION
SOIL TYPE
l0l"t
PLASTIC
INDEX
lbBfl
UNCONFINED
COMPRESSIVE
STRENGTH
PERCEiIT
PASStitG N0.
200 stEvE
l%l
LIQUID LII'IT
NATUML
DRY
DENSITY
locll
GRAVEL
("t"1
SAND
(%)BORING
aftl
DEPTH
NATURAL
itotsTuRE
CONTENI
Very Sandy Clay16.9 108I2v,
Very Sandy Clay50510.2 ll0
Very Clayey Sand62383.1 10015
Very Sandy Clay1042l07.7
Sand and Clay505.1 10815