HomeMy WebLinkAboutSubsoils Report for Foundation DesignI .*rt Hiç1fi'çffËf*rÊ;;**'
Ån FmployEa Owned Campeny
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
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 43, FOUR MILE RANCH
186 MAROON DRIVE
GARFTELD COUNTY, COLORADO
PROJECT NO.2t-7-676
NOVEMBER 5, 2021
PREPARED FOR:
LUIS BAILON
4063 COTJNTY ROAD 37
BRTGHTON, COLORADO 80603
cbailonL4@email.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS.....
FIELD EXPLORATION
UNDERDRAIN SYSTEM
SURFACE DRAINAGE
...............- I -
1
I
,.,..- 2 -
SUBSURFACE CONDITIONS ...a
FOI.INDATION BEARING CONDITIONS ......
DESIGN RECOMMENDATIONS............... .....- 3 -
FOUNDATIONS ........- 3 -
FOUNDATION AND RETAINING WALLS .................- 4 -
FLOOR SLABS -5-
-5-
-6-
LIMITATIONS 6-
FIGURE I - LOCATION OF EXPLORATORY 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
Kumar & Associates, lnc. @ Project No. 21-7-676
PURPOSE AND SCOPE OF'STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on
Lot 43, Four Mile Ranch, 186 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 Luis Bailon dated August 17,2021.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils obtajned 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, 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 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 described 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. The building envelope was staked in the
field. The lot slopes moderately to strongly down to the west at l0 to l5o/o grade. Vegetation
consists of sage brush, grass and weeds. There were scattered basalt cobbles and small boulders
on the ground surface.
Kumar & Associates, lnc. @ Project No. 2'l-7-676
a
FIELD EXPLORATION
The field exploration for the project was conducted on October 4,2021. 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-
mounted CME-458 drill rig. The borings \Ã/ere 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-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 retumed 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 1 foot oftopsoil, consist ofabout 2Yz to 3Yz feet of sandy clay overlying siþ
sandy gravel with cobbles and small boulders. At Boring 1, there was 8/, feet of silty sand
overþing the dense gravel soil. Drilling in the dense granular soils with auger equipment was
difficult due to the basalt cobbles and boulders and drilling refusal was encountered in the
deposit in both borings.
Laboratory testing performed on samples obtained from the borings included natural moisture
content, density and percent finer than sand size gradation analyses. Results of swell-
consolidation testing performed on a relatively undisturbed drive sample of the shallow stiff clay
soils from Boring 2, presented on Figure 4,indicate low compressibility under light loading and
a low to moderate swell potential 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
slightly moist.
FOUNDATION BEARING CONDITIONS
Foundations should bear on the silty sand and silty sand and gravel soils encountered in the
borings at depths of 3%to 4Yz feet. The topsoil and shallow expansive clay soils should be
Kumar & Associates, lnc. @ Project No.21-7.676
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removed from below all footing and slab areas. If needed, imported structural fill such as3/¿-inch
road base can be placed below footing and slab 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 footings bearing
on the natural granular soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 2,000 psf. Based on experience, we expect
settlement of footings O"rigrr"dãñãl-cted 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
aÍea.
-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 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 area should then be moistened and compacted.
If water seepage is encountered, the footing areas should be dewatered before
concrete placement. If needed, structural fill consistingof 3/t-inchroad base can
be placed and compacted in thin lifts to at least 98o/o of the maximum standard
Proctor density at a moisture content near optimum to re-establish design footing
grades.
Kumar & Associates, lnc. @ Project No.21-7-676
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A representative of the geotechnical engineer should observe all footing
excavations 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 50 pcf for backfill consisting
of the on-site granular 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 granular soils.
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 90Yo of the maximum
standard Proctor density at a moisture content near optimum. Backfill in pavement and walkway
areas should be compacted to at least 95Yo 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 coefficient of friction of 0.45. 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
6)
Kumar & Associates, lnc. @ Project No. 21-7-676
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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 and the shallow clay soils, 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 to facilitate drainage.
This material should consist of minus 2-inch aggregate with at least 50% retained on the No. 4
sieve and less than 2Yo passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least95Yo 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.
LINDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
mountainous areas 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 ofthe 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 lo/o to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2%o 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 lYzfeet deep.
Kumar & Associates, lnc. @ Project No.21-7-676
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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
at least 95o/o of the maximum standard Proctor density in pavement and slab areas
and to at least 90Yo 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. Consideration should be given to use of xeriscape
to reduce the potential for wetting of soils below the building caused by inigation.
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 different from those described in this repori, we should be notified so
that re-evaluation of the recommendations may be made.
Kumar & Associates, lnc. @ Project No. 21-7-676
-7 -
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 &
-<-'
Daniel E. Hardin,
DEFVkac
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Kumar & Âsso*iates, lnc. o Project No.21-7.6T6
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BORING 1
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APPROXIMATE SCÀLE-FEET
21 -7 -67 6 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
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EL. 1 00'
BORING 2
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21 -7 -676 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
LEGEND
N
TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, SLIGHTLY MOIST, DARK BROWN
CLAY (CL); S|LTY, SANDY, VERY ST|FF, SLTGHTLY MO|ST, BROWN
SAND (SM); SILTY, MEDIUM DENSE, SLIGHTLY MO|ST, BROWN, SLIGHTLY CALCAREOUS.
GRAVEL (GM); WITH COBBLES, SANDY, SILTY, POSSIBLE BOULDERS, DENSE, SLIGHTLY MOIST,
MIXED BROWN.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE
DRTVE SAMPLE, 1 S/9-|NCH t.D. SPLTT SPOON STANDARD PENETRATTON TEST.
1z./1. DRIVE SAMPLE BLOW COUNT. INDICATES THAT 13 BLOWS OF A 14O-POUND HAMMER'"1 ,. FALLING 30 INcHES wERE REQUIRED To DRIVE THE SAMPLER 12 INcHES.
f eucrrcAL AUGER REFUSAL.
NOTES
1, THE EXPLORATORY BORINGS WERE DRILLED ON OCTOBÊR 4, 2021 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.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER
TO THE GROUND SURFACE AT BORING I AS ELEVATION 1OO' FEET.
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) (ASTV D2216);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM Dl140);
NV = NO LIQUID LIMIT VALUE (¡STU O¿SIA);
NP = NON-PLASTIC (ASTM 04518).
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21 -7 -676 Kumar & Associates LEGEND AND NOTES Fig. 5
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No. 21-7-676
Silty Sand
Sandy Clay
SOIL TYPE
Silty Sand
(%l
EXPANSION
1.8
(psf)
EXPANSION
PRESSURE
8,000
lo/.1
PLASTIC
INDEX
NP
ATTERBERG LIMITS
LIQUID LIMIT
lø/.1
NV
PERCENT
PASSING NO.
2()O SIEVE
35
(%)
SAND
GRADATION
(%)
GRAVEL
(ocf)
NATURAL
DRY
DENSITY
110
t28
(o/ol
NATURAL
MOISTURE
CONTENT
3.4
6.5
JJ3.751
01
2y,
ftt
DEPTH
SAMPLE LOCATION
BORING
2