HomeMy WebLinkAboutSubsoil Study for Foundation Design 05.23.2024lCAffi,ffiHftrtr1,$f;n**
An Employcc Owncd 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
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SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 6, RAPIDS ON THE COLORADO
RAPIDS VIEW LANE
GARFIELD COUNTY, COLORADO
PROJECT NO.24-7-272
MAY 23,2024
PREPARED FOR:
JOSE LEON AND EUSTOLIA VALADEZ
731 STORM KING CIRCLE
NEW CASTLE, COLORADO 81647
eustvh@yahoo.com
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TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS..
FIELD EXPLORATION..
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS ...................
FOTINDATIONS
FOLINDATION AND RETAINING WALLS
FLOOR SLABS
I.INDERDRAIN SYSTEM
SURFACE DRAINAGE...
LIMITATIONS...........
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 . SWELL-CONSOLIDATION TEST RESULTS
FIGURE 4 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Associates, lnc, @ Project No. 24-7-272
PURPOSE AND SCOPE OF STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on Lot 6,
Rapids on the Colorado, Rapids View Lane, 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 Jose Leon and Eustolia Yaladez dated April 26,2024.
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
Plans for the proposed residence were conceptual at the time of our study. The proposed
residence is assumed to be a one- or two-story structure with an attached garage. Ground floors
could be structural over crawlspace or slab-on-grade. Grading for the structure is assumed to
be relatively minor with cut depths between about 2 to 4 feet. We assume relatively light
foundation loadings, typical of the proposed type of construction.
When 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 subject site was vacant at the time of our field exploration. The ground surface was
realatively flat and nearly level in the southeast portion of the lot and gently sloping down
toward the Colorado River at grades estimated at between 5 and 15 percent in the northwest
portion of the lot. Vegetation consists of grass and weeds.
FIELD EXPLORATION
The field exploration for the project was conducted on May 7 ,2024. 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 augers powered by a truck-
mounted CME-458 drill rig. The borings were logged by a representative of Kumar &
Associates, Inc.
Kumar & Associates, lnc. @ ProJect No, 24-7-272
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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. The
subsoils encountered below about Yzfoot oftopsoil consist ofsilty sand to about 4 feet deep
overlying denseo silty sandy gravel and cobbles to the maximum drilled depth of 6Yz feet.
Drilling in the coarse granular soils with auger equipment was difficult due to the cobbles
and boulders and drilling refusal was encountered in the deposit.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and gradation analyses. Results of swell-consolidation testing performed
Ona relatively undisturbed drive sample of the silty sand soil, presented on Figure 3, indicate
initial low compressibility under light loading and moderate compressibility under conditions of
loading and wetting. Results of gradation analyses performed on small diameter drive samples
(minus lY'-inch fraction) of the coarse granular subsoils are shown on Figure 4. The laboratory
testing is summarizedin Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to moist. It is our experience that groundwater level is within the underlying
gravel and seasonally fluctuates with flow in the Colorado River.
FOUNDATION BEARING CONDITIONS
The upper sand soils encountered in the borings possess low bearing capacity and low to
moderate settlement potential especially when wetted under load. The underlying coarse
granular soils possess moderate bearing capacity and typically low settlement potential. At
assumed excavation depths we expect the exposed subsoils to transition between sand and
gravel. The proposed residence can be supported on spread footings bearing on the natural soils
with a risk of differential settlement due to the variable bearing conditions between the sand and
gravel subsoils. Sand soils exposed at foundation bearing level should be moisture conditioned
and compacted prior to concrete placement.
Kumar & Associates, lnc. @ Project No,24-7-272
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DESIGN RECOMMENDATIONS
FOTINDATIONS
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 soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils should be designed for an
allowable bearing pressure of 2,000 psf. Based on experience, we expect
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less. The settlement risk can be limited by extending the
bearing level completely down to the dense gravel.
2) The footings should have a minimum width of 18 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.
4) Continuous foundation walls should be well reinforced top and bottom to span
local anomalies and resist differential movement such as by assuming an
unsupported length of at least L2 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) Topsoil and any loose disturbed soils should be removed and the footing bearing
level extended down to the firm natural soils. The exposed sand soils in footing
areas should then be scarified, moisture conditioned and compacted.
6) A representative ofthe 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 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, 24-7-272
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All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffrc, 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. Backfill placed in pavement and
walkway areas should be compacted to at least 95o/o 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 causs 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 0.35. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 375 pcf. The
coeffrcient 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 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 (if provided) to facilitate drainage.
This material should consist of minus 2-inchaggregate with at least 50% retained on the No. 4
sieve and less than 2o/o passing the No. 200 sieve.
All fill materials for supporl of floor slabs should be compacted to at least 95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fillcan consist of the
on-site granular soils devoid of vegetation, topsoil and oversized rock.
Kumar & Associates, lnc. @ Project No. 24-7-272
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LINDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area that the groundwater level can rise and 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 areas deeper than 3 feet and basement areas (if any), be protected from wetting and
hydrostatic pressure buildup by an underdrain system. If a basement is proposed, the feasibility
of keeping the floor level at least 1 to 2 feet above high water level should be evaluated before
building excavation.
The drains should consist of rigid perforated PVC 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 eachlevel of excavation and at least 1 foot below lowest adjacent finish grade and
sloped at a minimum %o/o to a suitable gravity outlet. Free-draining granular material used in the
underdrain system should contain less than 2oh 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 IYz feet deep.
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 andunderslab areas 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 90o/o 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 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
backfill.
5) Landscaping which requires regular heavy irrigation should be located at least
10 feet from foundation walls.
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.
Kumar & Associates, lnc. @ Project No.24-7-272
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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 prepmed for the exclusive use by our client for design pu{poses. 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 strata and testing of structural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
Kumar & Associates,
James H. Parsons,
Reviewed by:
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Steven L. Pawlak, P.E.
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Kumar & Associatee, lnc. o Projecl No.24-7-272
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[:ound rebor wiih oluminum
cop, PLS No. 13501
Witness corner
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Found rebor with oluminum
cop, PLS No. 1J501
25
APPROXIMATE SCALE-FEET
24-7 -272 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
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BORING 1
EL. 1 00'
BORING 2
EL. 99.5'
0 0
18/ 12
WC=7.3
-20O=47
35/4, 15/o
16/ 12
WC=3.3
DD=101
32/s, 15/0
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LEGEND
TOPSOIL; SILT, SANDY, SCATTERED GRAVEL, ORGANICS, FIRM, MOIST, DARK BROWN.
SAND (SM); STLTY TO VERY S|LTY, GRAVELLY, MEDTUM DENSE, SLTGHTLY MO|ST, BROWN
GRAVEL AND COBBLES (GM); SANDY, SILTY, DENSE, SLIGHTLY MOIST, BROWN.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
DRTVE SAMpLE, I 5/8-INCH t.D. SPLtr SPOON STANDARD PENETRATTON TEST.
1a/1t DRIVE SAMPLE BLOW COUNT. INDICATES THAT 18 BLOWS 0F A 14O-POUND HAMMER.-/ '. FALLING 30 INCHES WERE REQUIRED To DRIVE THE SAMPLER 12 INCHES.
f enacrrcnL AucER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON MAY 7,2A24 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 BENCHMARK ON FIG. 1.
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 EXPTORATORY 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 DENSTTY (pcr) (ASTU D2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM 06915);
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM Dl140).
i
WC=3.3
+4=45
-200= 1 6
24-7 -272 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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SAMPLE 0F: Silty Sond
FROM:Boring2@2'
WC = 5.3 %, DD = 101 pcf
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ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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I 1.0 APPLIED PRESSURE - KSF 10
24-7 -272 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5
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OF PARTICLES IN
CLAY TO SILT COBBLES
GRAVEL 15 % SAND
LIQUID LIMIT
SAMPLE OF: Sllty Very Sondy Grovel
59%
PLASTICITY INDEX
SILT AND CLAY 16
'6
FROM: Borlng 2 O 1' ond 5.5' (Comblned)
Tha$ l.sl rolull! qpply only lo lh.!ompl.! vhlch weru loahd, Thcf.tllng ruporl sholl nol b. rcprcduc.d,
.xolpl ln lull, vllhoul lhr wrlllcn
opprcvol ol Kumor & Alaoolot r. lno.
Shvr qnqlyllr t lllng l! plrfomld ln
occordonc. wlth ASTH 06915, ASTII D7928,
ASTM C156 snd,/or ASTM 01140,
SIEVE ANALYSISHYDROMETER ANALYSIS
U.S. STANOARO SERIES cgR sQufiE oPExtNos
tr^r ttt 1 1r.a
flrE iEAO[{oS
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SAND GRAVEL
FINE MEDIUM IcoARSE FINE COARSE
24-7 -272 Kumar & Associates GRADATION TEST RESULTS Fig. 4
rcn l(umr & Associates, [rc.E
Geotechnical and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORYTEST RESULTS
Project No.24-7-272
SOIL TYPE
Silty Sand
Silty Sand
Silty Very Sandy Gravel
UNCONFINED
COMPRESSIVE
STRENGTH
{mfl
47
ATTERBERG LIMITS
PLASTIC
INDEX
(olol
LIQUID LIMIT
llJ
PERCENT
PASSING NO.
200 stEvE
t6
SAND
(%)
39
GRAVEL
vt
45
NATURAL
DRY
DENSIW
{pcfl
I 0 1
NATURAL
MOISTURE
CONTENT
t%l
7.3
aaJ.J
J.J
SAMPLE LOCATION
DEPTH
{ft}
2
2
4 and5Y,
Combined
BORING
I
2