HomeMy WebLinkAboutSubsoils Report for Foundation DesignlGrtiiçl['fftffffi*¡!iÊ;'*"'
An Employcc onrncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax; (970) 945-8454
email: kaglenwood@kumarusa.com
wwwkumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
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SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
PARCEL 217916400440
COT]NTY ROAD 331
GARFIELD COUNTY, COLORADO
PROJECT NO.23-7-388
AUGUST 9,2023
PRAPARED FOR:
JOSE CHAVEZ
50323 COUNTY ROAD 336, TRAILER 33
NE\M CASTLE, COLORADO 81647
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TABLE OF'CONTENTS
PURPOSE AND SCOPE OF STUDY ..,............. 1 -
PROPOSED CONSTRUCTION
SITE GRADING.......
LIMITATIONS...
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 1- SUMMARY OF LABORATORY TEST RESULTS
....- 1 -
SITE CONDITIONS...,....,.i..- t
FIELD EXPLORATION .,,.....I
SUBSURFACE CONDITIONS 2-
DESIGN RECOMMENDATIONS ..-2-
FOLTNDATIONS .....n
FOTINDATION AND RETAINING WALLS .................. 3 -
FLOOR SLABS -4-
-\-
5
Kumar & Associates, lnc. @ Project No.23-7-388
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located at Parcel
217911,6400440, County Road 331 (Dry Hollow Road). The project site is shown on Figure l.
The purpose of the study was to develop recommendations for the foundation design, The study
was conducted in accordançe with our agreement for geotechnical engineering services to Jose
Chavez dated lune 26, 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 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- or two-story structure possibly over a walkout basement
level with an attached garage located approximately in the area of the exploratory borings
shown on Figure 1. Ground floor will be slab-on-grade or structural over crawlspace. Grading
for the structure is assumed to be relatively minor with cut depths between about 4 to I feet. We
assume relatively light foundation loadings, typical of the proposed type of construction.
V/hen building location, grading and loading information have been developed, we should be
notified to re-evaluate the recommendations presented in this report.
SITE CONDITIONS
The project site was vacant at the time of our exploration, Topography at the site is hilltop with
moderately sloping terrain down to the east. Elevation difference açross the proposed building
area is about 3 feet. Vegetation at the site consists of native grass and weedso sage brusho and
pinon and juniper trees.
FIELD EXPLORATION
The field exploration for the project was conducted on July 7, 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-
mounted CME-45B drill rig. The borings were logged by a representative of Kumar &
Associates,Inc.
Kumar & Associates, lnc. @ Project No. 23-7-388
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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.
Beneath about one foot of topsoil, the subsoils consist of about 3 to 5 feet of stiff, slightly sandy
silty clay overlying relatively dense, silty sand and gravel with cobbles and probable boulders.
Laboratory testing performed on samples obtained from the borlngs included natural moisfure
content and density and gradation analyses. Results of swell-consolidation testing performed on
relatively undisturbed drive samples of the upper sandy clay soils, presented on Figures 4 and 5,
indicate lorv to moderate compressibility under conditions of loading and wetting and a low
hydrocompression potential of the sample form Boring I and a low expansion potential in the
sample from Boring 2, when wetted under a constant 1,000 psf surcharge. Results of gradation
analyses performed on small diameter drive samples (minus l%-inch fraction) of the coarse
granular subsoils are shown on Figure 6. The laboratory testing is summarizedin Table 1.
No free water was encountered in the borings at the time of drillìng and the subsoils \ryere
slightly moist to moist.
DESIGN RECOMMENDATIONS
FOLINDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recofirmend the building be founded with spread footings bearing
on the natural granular soils beneath the upper fìne-grained soils.
The design and construction uiteria 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 2,500 psf. Based on experience, we expect
settlement of footings designed and constructed as discussed in this section will
be about I inch or less.
2) The footings should have a minimum width of 16 inches for continuous walls and
2 feet for isolated pads.
3) Exteríor footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
Kumar & Associates, lnc. o Projec't No.23-7-388
-J-
4)
of foundations at least 36 inches below exterior grade is typically used in this
area.
Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 10 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.
All existing fill, topsoil, fìne grained 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 area should then be moistened
and compacted.
A representatíve 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 suffïciently 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 granular soils,
All foundation and retaining structures should be designed for appropriate hydrostatic and
surchæge 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 90o/o of the maximum
standard Proctor density at a moisture content near optimum. Backfill in pavement and walkway
areas should be compacted to at least 95% 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
backfìll should be expected, even if the material is placed correctly, and could result in distress
to facilities constructed on the backfïll.
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
5)
6)
Kumar & Associates, lnc. @ Project No.23-7-388
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the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated
based on a coeffìcient 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 400 pcf. The
coefficient of friction and passive pressure values recommended above assume ultimate soil
strength. Suilable factors of safety should be included in the design to limit the strain which will
occur at the ultimate strength, particularly ín the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads should be a nonexpansive material compacted to at
least95o/o 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 with a low risk of post-construction movement. A lower risk of movement would
be to place 2 feet of compacted structural fill beneath slabs-on-grade. 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 bc 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 2Vo passingthe 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 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
the area 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 surounded above
the invert level with free-draining granular material. The drain should be placed at each level of
excavation and at least I foot below lowest adjacent finish grade and sloped at a minimum lYoto
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2o/o passingthe 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 l%feet deep and covered
with filter fabric such as Mirafi 140N or 160N.
Kumar & Associates, lnc. @ Project No.23-7-388
5
SITE GRADING
The risk of construction-induced slope instability at the site appears low provided the building is
located as planned and cut and fill depths are limited. We assume the cut depths for the
basement level will not exceed one level, about 10 to 12 feet, Fills should be limited to about
8 to 10 feet deep, especially at the downhill side of the residence where the slope steepens.
Embankment fills should be compacted to at least 95a/o 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 the portions of the hillside exceeding
20% grade.
Permanent unretained cut and fïll slopes should be graded at?horizontal to I vertical or flatter
and protected against erosion by revegetation or other means. The risk of slope insøbility will
be increased if seepage is encountered in cuts and flatter slopes may be necessary. If seepage is
encountered in permanent cuts, an investigation should be conducted to determine if the seepage
will adversely affect the cut stability. This office should review site grading plans for the project
prior to construction.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
1) Inundation of the foundation excavations and underslab æeas 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. Vy'e recommend a minimum
slope of 6 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
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
backfì11.
5) Landscaping which requíres regular heavy inigation should be located at least
5 feet from foundation walls.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this area afthis time, We make no warranty either express or implied
Kumar & Associates, lnc. @ Project No.23-7-388
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The conclusions and recoillmendations submitted in this report are based upon the 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 determining the
presence, 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
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 beçome evident until excavation is performed. If conditions encountered
during construction appear different from those dessibed 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 veriff 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,
Robert L. Duran,
Reviewed by:
b
Daniel E. Hardin, P.E
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Kumar & Associates, lnc. ô Project No. 23-7-388
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23-7-388 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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LEGEND
TOPSOIL¡ SILTY, CLAYEY, SANDY, ROOTS/ORGANICS, LOOSE, SLIGHTLY MOIST, LIGHT BROWN.
CLAY (CL); SILTY, SLIGHTLY SANDY, VERY STIFF, SLIGHTLY MOIST, LIGHT BROWN.
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SAND AND GRAVELS (SM-GM): S|LTY, SLTGHTLY CLÀYEY, DENSE TO VERY DENSE, SLTGHTLY
MOIST, TAN.
DRIVE SAMPLE, z.INCH I.D. CALIFORNIA LINER SAMPLE.
I DRTVE SAMPLE, 1 3/A-|NCH r.D. SPLrr SPOON STANDARD PENETRATTON TEST.
ı4 t.. DRIVE SAMPLE BLOW COUNT. INDÍCATES THAT 21 BLOWS OF A 140-POUND HAMMERztt t1 FALLTNG Jo rNcHEs WERE REQUTRED To DRtvE THE SAMPLER f 2 tNcHES.
NOrEs
1. THE EXPLORATORY BORINGS WERE DRILLED ON JULY 7, 2025 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 MEASURED BY HAND LEVEL AND REFER
TO THE BORING I WITH AN ASSUMED ELEVATION OF 1OO,FEET.
4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SI{OULD BË CONSIDERED ACCURATE
ONLY TO THE DEGREE IMPLIED BY TI.{E METI{OD USED.
5. TI{E 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 ÊORINGS AT THE TIME OF DRILLING.
7, LABORATORY TËST RESULTS¡
wc :: WATER CONTENT (X) (ASTM D2216)¡
DD = DRY DENSITY (PCf) (ASTM D2216)i
+4 = PERCENTAGE RETAINED ON No. 4 SIEVE (ASTM 06915);
-200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140).
25-7-388 Kumar & Associates LEGEND AND NOTES Fig. 3
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SAMPLE OF: Slightly Sondy Sllty Cloy
FROM:Borlng1O2.5'
WC = 10.9 96, DD = 109 pcf
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23-7-388 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
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SAMPLE OF: Slightly Sondy Cloy
FROM;Boring2@5'
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EXPANSION UNDER CONSTANT
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23-7-388 Kumar & Associates GRADATION TTST RESULTS Fig. 6
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Geotechnical and Materials Engineers
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TABLE I
SIIilIIARY OF I.ABORATORY TEST RESULTS
SqtTYPE
Slightly Sandy Silty Clay
Silty Sand and C¡ravel
Slightly Sandy Silty Clay
Slightly Sandy Clay
Silty Gravelly Sand
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110
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