HomeMy WebLinkAboutSubsoil Studyl(+rlffiiilffiffiixü--
An Emdoycc Owncd ComPonY
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945'7988
fax (970) 945-84s4
email: kaglenwood@kumarusa.com
www.kumarusa.corn
Ofiìce Localiors: Denver (HQ), Par*er- Cotorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED KLASE RESIDENCE
LOT 12, BLOCK 4, BATTLEMENT CREEK VILLAGE
I2I BOULDER RIDGE
GARFIELD COUNTY, COLORADO
PROJECT NO.2l-7-121
FEBRUARY 12,2021
PREPARED FOR:
RUSSELL CARTWRIGHT
35 WILLO1VVIEW \ryAY
PARACUTE, COLORADO 81635
russecart(Osmail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION .........
SITE CONDITIONS...
FIELD EXPLORATION
SUBSURFACE CONDITIONS
DESIGN RECOMMENDATIONS
FOUNDATIONS ..........
FOUNDATION AND RETAINING WALLS
FLOOR SLABS
UNDERDRAIN SYSTEM .,....
SURFACE DRAINAGE
LIMITATIONS ..........
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2. LOG OF EXPLORATORY BORING
FIGURE 3 - SWELL-CONSOLIDATION TEST RESULTS
TABLE 1. SUMMARY OF LABORATORY TEST RESULTS
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Kumar &Assoclates, lnc. o Project No. 214-121
PT}RPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for the proposed Klase residence to be located
on Lot 12, Block 4, Battlement Creek Village, 121 Boulder Ridge, Garfreld County, Colorado.
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 accordance with our
agreement for geotechnical engineering services to Russell Carh,vright dated January 12,2021.
An exploratory boring was drilled to obtain information onthe subsurface conditions. Samples
of the subsoils obtained during the field exploration were tested in the laboratory to determine
their classifrcation, compressibility or swell and other engineering characteristics. The results of
the fiçld 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 conçlusions, design
recommendations and other geotechnical engineering considerations based on the proposed
construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
The residence will be a single-story wood frame structure over a walkout basement level with
attached garageat the main level. Ground floors will be slab-on-grade. Grading for the structure
is assumed to be relatively minor with cut depths between about 2 to 8 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 recommerdations contained in this report.
SITE CONDITIONS
The lot was vacant and the ground surface appeared mostly natural at the time of our field
exploration. The terrain is strongly sloping down to the south. Vegetation consisted of grass,
weeds and sagebrush. The Colorado River is approximately Ya mile north of the site and
considerably lower in elevation.
Kumar & Aseociales, lnc. o Prqú.Nø.21-7-121
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FIELD EXPLORATION
The field exploration for the project was conducted on January 14,2021. One exploratory
boring wæ drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The
boring was advanced with 4 inch diameter continuous flight augers powered by a truck-mounted
CME-458 drill rig. The boring was logged by a representative of Kumar & Associates.
Samples of the subsoils were taken with 1% 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-l58ó.
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 Log of Exploratory Boring, Figure 2. The samples were retumed to our laboratory
for review by the project engineer and testing.
SUBSURFACE CONDITIONS
A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The
subsoils consist of about I foot of topsoil overlying very stifl sandy clayey silt to 12 feet depth
where underlain by relatively dense, silty clayey sandy gravel and cobbles with boulders down to
the drilled depth of l8 feet.
Laboratory testing perfbrmed on samples obtained from the boring included natural moisture
content and density, and f,ner than sand grain size gradation analyses. Results of swell-
consolidation testing performed on a relatively undisturbed drive sample of the clayey silt,
presented on Figure 4, indicate low to moderate compressibility under existing moisture
conditions and light loading, with a low expansion potential when wett€d under çonstant light
surcharge. The laboratory testing is summarized in Table l'
No free water was encountered in the boring at the time of drilling and the subsoils were slightly
moist.
Kumar &Associates, lnc. o Project tlo.2l-7-l2l
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DESIGN RECOMMENDATIONS
FOTJNDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the nature of
the proposed construction, we believe the building can be founded with spread footings bearing
on the natural soils with some risk of movement. The risk of movement is primarily if the
bearing soils were to become wetted and precautions should be taken to prevent wetting. Based
on our experience in the area, the clayey silt soils are not expansive.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
l) Footings placed onthe undisturbed natural soils should be designed for an
allowablebearingpressure.P.Basedonexperience'weexpect
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less. Some additional settlement could occur if the bearing
soils become wetted. The magnitude of the additional settlement would depend
on the depth and extent of the wetting but may b e on the order of táto I inch.
Z\ 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 foundationr u*191:6 i*hæ-below exterior grade is typically used in this
area.
4) Continuous foundation walls should be well reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 14 feet.
Foundation walls acting as retaining structures should also be designed to resist
laterat earth pressures as discussed in the "Foundation and Retaining Walls"
section of this rePort-
5) All existing frll, topsoil and any loose or disturbed soils should be removed and
the footing bearing level extended down to the firm natural soils. The exposed
soils in footing area should then be moistened and compacted.
6) A reprosentative oftho geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
Kumar & Associatæ, lnc. o ProiæINo.21-7.121
-4
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 mobilíze 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.
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 90% of the maxrmum
standard proctor density at a moisture content near optimum. Backfill 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 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 tho 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 coeffrcient of friction of 0.35. Passive pressure of compacted backfrll 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 assums 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 agâinst
Kumar & Associatee , lnc. o Project llo. 21-7-121
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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 natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade
construction. The clayey silt soils are typically compressible when wetted and precautions
should be taken to prevent wetting of the subgrade soils. Designing the slab for expansive
çonditions is not needed based on our experience in the area'
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
2% passing the No. 200 sieve.
Alt 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 soils devoid of vegetation, topsoil and oversized rocks'
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience ln
the area that local perched groundwater can develop during times of heavy precipitation or
seasonal runoff, Frozen ground during spring runoffcan also 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 I foot below lowest adjacent finish grade and sloped at a minimum l% to
Kumar & Associates, lnc. o Project No.21-7-121
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a suitable gravrty outlet. Free-draining granular material used in the underdrain system should
contain less than 2% passing the No. 200 sieve, Iess 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.
SURFACE DRAINAGE
Positive surface drainage is a very important aspect of the project to prevent wetting of the
bearing soils. The following drainage precautions should be observed during construction and
maintained at all times after the residence has been completed:
l) Inundation ofthe foundation excavations and underslab areas should be avoided
during construction.
Z) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95%o of the mæ<imum standard Proctor density in pavement and slab areas
and to at least 90% ofthe maximum standard Proctor density in landscape areas.
3) The ground surface surrounding the exterior of the building should be sloped to
drain away ûom the foundation in all directions. We recommend a minimum
slope of 12 inches in the first l0 feet in unpaved areas and a minimum slope of
3 inches in the first l0 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, such as sod, and lawn
sprinkler heads should be located at least 10 feet from foundation walls.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engíneering
principles and practices in this area at this time. We make no waranty either express or implied.
The conclusions and recommendations submitted in this report are based upon the data obtained
from the exploratory boring drilled at the location 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
Kumar & Associates, lnc. o Project l{o.21-7-121
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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 extrapolation of the subsurface conditions
identified at the exploratory boring and variations in the subsurface conditions mây not become
evident until excavation is performed. If conditions encountered during consfruction 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 pmject 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, trnc.
James H. Parsons, E.I.
Reviewed by:
David A. Young,
JFIPlkac
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Kumar & Associates, lnc. ú Project No.21"7.121
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APPROXIMÀTE SCALE.FEET
Fig. 1LOCATION OF EXPLORATORY BORING21 -7 -121 Kumar & Associates
BORING 1 LEGEND
0
TOPS0IL; SANDY CLAYEY SlLi WITH ORGANICS, FIRM, MO|ST,
BROWN.
35/12
SILT (ML); CLÂYTY, SANDY, VERY STIFF TO STIFF, SLIGHTLY
MOIST, TÀN.
5
zaln
WC=3.8
0D=89
-200=84 ffi
F
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GRAVEL (GC-GM); WITH BASALT ROCKS TO COBBIT AND
BOUTDER SIZE, SANDY, CLÀYff, SILTY, DENSE, SLIGHTLY MOIST,
UGHT BROWN.
21/12
WC=4.7
DD=l 03
le/12
WC=3.8
DD=99
-200=86
DRIVE SAMPIT, z-INCH I.D. CAUFORI.IIA UNER SAMPI.E.
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10 DRtVt SAMPLE, r 3/8-INCH l,Ð. SPUT SP00N STANDAR0
PENETRATION TEST.
15
,"r.^DRIVE SAMPLE BL0w COUNT. INDICATES THAT 55 BLOWS 0F14 tL
^ 140-pouND HAMMER FALLING J0 tNcHEs WERE REoUIRED
TO DRIVE THE SAMPTER 12 INCHES.
I pRlcncr AUGER REFUsÀ1.
I
50/t.s
50/.25
NOTES
I. THT EXPLORATORY BORING IVAS DRILLED ON JANUARY 14,2O2I
WTH A 4-INCH DIAMETER CONTINUOUS FTIGHT POWER AUGER.
20 2. THT LOCATION OF THE EXPLORATORY BORING WAS MEASURED
APPROXIMATILY BY PACING TROM FEAIURES SHOWN ON THE
SIÍE PI.ÀN PROVIDED,
3. THE ELEVATION OF THE EXPLORATORY BORING WÀS NOT
MËASURED AND THT LOG OF THE EXPLORATORY BORING IS
PLOTTED ÏO DEPTH.
1. THE EXPLORATORY BORING LOCATION SHOULD BE CONSIDEREO
ACCURATT ONLY TO THE OEGREE IMPLIED BY THE METHOD
USTD.
5. THE LINTS BET'IIETN MATERIALS SHOWN ON THE TXPLORATORY
BORING LOG REPRESENT THE APPROXIMATE BOUNDÀRIES
BETWEEN MATERIÀL TYPES AND THE TRANSITIONS MAY BI
GRADUAL.
6. GROUNDWATER WÂS NOT TNCOUNTERED IN THE BORING ÀT ÏHg
TIME OF DRILUNG.
7. LÁBORATORY TESÏ RESULÏS:
WC = IYATER CONTENT (16) (ASTM D 2216);
DD = DRY DENSIw (pcf) (ASTM D 2216);
-200 = PERCENTÀGE PASSING N0. 200 SIEVE (ÀsTM Ð 1t40).
Fig. 2LOG OF EXPLORATORY BORINGKumar & Associates?1 -7 -121
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SAMPLE OF: Sondy Cloyey Sill
FROM:Boringl@.7'
WC = 4.7 %, ùD = 103 pcf
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21-7-121 Kumar & Associates SWELL-CONSOLIDATION TEST RESULT Fig. 3
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TABLE I
SUMMARY OF LABORATORY TEST RESULTS
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Sandy Clayey Sílt848943.8I
Sandy Clayey Silt4.7 1037
Sandy Clayey Silt8699l03.8