HomeMy WebLinkAboutSoils ReportColleen W¡fthFrom:Sent:To:Cc:Subject:Attachments:HiColleen,Attached is the soils report for the Nilsson propertyPlease call with any questions.Thank you,Brad HancockOddo Engineeríngo (e70) e4s-1006c (s70) 3ss-4706Brad Hancock <Brad@oddogws.com>Tuesday, September 6, 2A22'1 2:09 PMColleen Wifthalan@woodstoneinc.net; 'John Howard'; 'Bob Oddo';snn@gwsford.com; Sam lrmen[External] RE: BLRE-08-22-7742 Nilsson new residence, lot 2, Riveruiew Ranch SubdivisionS KM_C45822060903220.pdfâarrecfaa/at ¿eKvnar refar/faâêt,te/ ?4-Z?
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An Employcç Ownad Compor¡y
5020 Connty Rerad 154
Clenrvor¡d Springs, CO 8lltOl
phone: {970) 945-79¡18
fax: (970) 94-5-8454
email : kaglenwood@kurnarusa.conr
wç'w. kr;rna¡usa. co¡n
Offiee l¡eatio¡s: Denver (HQ), Farker, Colorada Springs. Fort Collins. Clenwood Springs. and Sutlinrii Caunty, Colorado
SIIBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESII'ENCE
LOT 2, Rr\rER VIEW RANCH SUBDTVISION
167 SIIORE DRIVE
GARFIETD COUNTY, COLORADO
PROJECT No,22.7.29I
JUNE 9,2022
PREPARED FOR:
STEVE NILSSON
787 CAT\IYON CREEK DRIVE
GLENWOOD SPRTNGS, COLORADO 81601
ssn{n qwsford.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY 1
PROPOSED CONSTRUCTION .........- 1 .
SITE CONDITIONS I
FIELD EXPLORATION -2-
SUB SURT'ACE CONDITIONS
FOUNDATION BEARING CONDITIONS
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FOUNDATIONS - {-
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FOUNDATION AND RETAINING WALLS .....
FLOOR SLABS........
UNÐERDRAIN SYSTEM
STIRFACE DRAINAGE.,.
LIMITATIONS
FIGURE 1 . LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURES 4 and 5 - SIVELL-CONSOLIDATION TEST RESULTS
TABLE T. SUMMARY OF LABORATORY TEST RESULTS
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PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located onLot2,
River View Ranch Subdivision, 167 Shore Drive, Garñeld 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 general accordance with our agreement for
geotechnical engineering services to Steve Nilsson dated April 14,2422.
A freld 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 subsurf¿ce conditions
encountered.
PROPOSED CONSTRUCTION
The proposed residence will be a single-story wood-frame structure over a walkout lower level
and garage at the main level with a detached secondary residence located as shown on Figure 1.
Ground floors will be slab-on-grade or structural above crawlspace. Grading for the structures is
assumed to be relatively rninor with cut depths between about 2 to 8 feet. We assume relatively
light foundation loadings, typical of the proposed type of construction.
Ifbuilding 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 building site was vacant at the time of our field exploration. The driveway access is off
Shore Drive which crosses the upper part of the lot. The ground surface through the building
area is gently sloping then drops steeply down around 25 feet to the shoreline trail then again
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down to the Colorado River as hdicated by thc contour lines on !'igure 1. Vegetation through
the building area consists of spalse grass and woeds.
FIELD EXPLORATION
Thc field exploration for the project was conducted on May n,2A22. Ttree 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.
Samples of the subsoils were taken with 1% inch and 2-inch LD. 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-I586.
The penehation 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
subsurface profile encountered in the borings was somewhat variable and consists of very stif{
slightly clayey, slightly sandy to sandy silt down to depths of about 26 to 27% feet in Borings I
and 3 and down to about 76%feetin Boring 2, underlain by dense silty sandy gravel and
cobbles. Similar subsoil profile is expected to extend down to near the shoreline trail. Drilling
in the coarse granular soils with auger equipment was difficult due to the cobbles and probable
boulders and drilling refiisal was encountered in the deposit at Boring 2.
Laboratory testing performed on samples obtained from the borings ineluded natural moisture
oontent and density, and finer than sand size gradation analyses. Results of swell-consolidation
testing performed on relatively undisturbed drive samples of the silt soils, presented on Figures 4
and 5, indicate low compressibility under natural low moisture content and light loading. The
samples showed rclatively minor compressibility or expansion potential when wetted under light
load and moderate compressibility under additional loading after wetting. The laboratory testing
is sumrnarized in Table 1.
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No free water was encountered in the borings atthe time of drilling and the subsoils were
typically slightly moist and moist with depth at Boring 3.
FOUNDATION BEARING CONDITIONS
The silt soils have low bearing capacity and generally moderate compressibility potential under
loading. Shallow spread footings placed on the natural soils can be used for foundation support
with a risk of settlement and distress mainly if the bearing soils are wetted. A deep foundation
such as micro-piles could be used to achieve a low settlement risk foundation and could be 15 to
20 feet or more in depth to reach suitable dense gtavel soils. If a deep foundation is desired, we
should be contacted for additional evaluation and recommendations.
The foundation bearing level should be set back from the steep slope adequate distance to not
adversely impact the slope stability. It appears a horizontal setback of I feet (edge of footing to
slope face) should be adequate provided construction activity does not disturb the slope. Surface
waler from the development should not be directed to the steep slope near the residence and be
by sheet flow rather than concentrated.
DESIGN RECOMMENDATIONS
FOUNÐATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, the building can be founded with spread footings bearing on the
natural soils with a risk of settlernent and diskess. Precautions should be taken to prevent
wetting of the bearing soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undishnbed natural soiis should be designed for an
allowable bearing pressure "ry-$Based on experience, we expect initial
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less. Additional differential settlement of around 1 to 2 inches
could occur depending on the depth and extent of wetting.
2) The footings should have a minimum width of 20 inches for continuous wall and
2 feet for isolated columns.
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3)Exterior footings and footings beneath unheated areas should be provided with
adequato soil cover above their bearing elcvation for frost protcction. Placcmcnt
of foundations at least 36 inches below exterior grade is typically used in this
area. ¡......5
Continuous foundation walls should be heavily reinforced top and bottom to spân
local anomalies such as by assuming an unsupported length of at least 14 feet and
built in a box-like configuration. 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.
The topsoil and any loose disturbed soils should be removed in the footing areas.
The exposed soils should then be moistened and compacted.
A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
4)
Foundation walls and retaining structures which are laterally supporled 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 55 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 45 pcf for backfill consisting of the on-site soils.
All tbundation and retaining structures should be designed 1'or appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffrc, construction materials and equipment. The
pressures recornmended above assume drained conditions behind the walls and a horizontal
backfill surface, The buildup of water behind a wall or an upward sloping baskfill surface will
inctease the lateral pressure imposed on a foundation wall or retaining structurc. An underd¡ain
should be provided to prevent hydrostatic pressr¡re buildup behind walls.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at near optimum moisture content. Backfill placed in pavement and
walkway areas should be compacted to at least 95% of the maximum standard Proctor density.
Carc should bc takcn not to overcompact the backfill or use large equþment near the wall, siuce
this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall
5)
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FOUNDATION AND RETAINING WALLS
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backfill should be expected, ev€n if'the material is placed correctly, and could result in distress to
facilities constructed on the backfill. Backfill should not contain organics, debris or rocks 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 0.35. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 325 pcf. The
coefficient of füction and passive pressure values recomme,nded above assumo ultimate soil
strength. Suitable factors of safety should be included in the design to limit the skain which will
occur at the ultimate strength, partieularly in the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads should be compacted to at least 95% of the
maxirrum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoii, can be used to support lightly loaded slab-on-grade
construction with a risk of settlement like that for footing foundations. To reduce the effects of
some differential movement, floor siabs 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 frec-draining gravel should bc 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. The gara5e slab should be underlainby 4 inches of road base.
All fill materials for support of floor slabs should be compacted to at least 95% ofmaximum
standard Proctor density at a moisture content near optimum. Required {ill can consist of the
onsite soils devoid ofvegetation, topsoil and oversized rock.
I'NDERDRAIN 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
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seasonal runoff. Ftozen grcund duliug s¡lriug ruuuff r:a¡r uluo oreute u perr-:hed uondition. Wc
recommend bclow-gradc construction, such as retaining walls ancl base,ment âreas, be protected
from wetting and hydrostatic pressure buildup by un undenlrain systom. If a shallow øawlspaco
is used (and around the garage)n an underdrain should not be provided to help keep the shallow
footings dry.
The drains should consist of 4-inch diameter perforated PVC pipe placed in the bottom of the
wall backfill sunounded above the invert level with free-draining granular material. The drain
should be placed at each level ofexcavation and at least 1 foot below lowest adjacent finish
grade and sloped at a minimum Yro/o to a suitable gravity outlet. Free-draining granular rnaterial
used in the underdrain system should contain less than 2% 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 lYz feet deep. An impervious membrane such as 20 mil PVC should be placed
beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to
prevent wetting of the bearing soils.
SURFACE DRAINAGE
Development of proper surface grading and drainage will be critical to keeping the bearing soils
dry and limiting building movetnent and distress throughout the building lifc. The following.
drainage precautions should be observed during construction and maintained at ¿ll times after the
residence has been completed:
1) Inundation ofthe foundation excavations and underslab areas shor¡ld be avoided
dwing construction.
2) Exlcriur b¿skfill should be atljusted to near optimum moisture and compacted to
at least 95o/o af 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 sunounding the exterio¡ 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 mininrum slops of 3
inches in the first 10 feet in paved areas. Free-draining wall backfill should be
covered with filter fabric and capped with at least 2 feet of the on-site soils to
reduce surface water infilhation.
4) Roof downspouts and drains should discharge well beyond the lirnits of all
backfill.
Kumar & Assoclates, lnç. @ Prolect No, 1S.7,291
Landscaping which requires regular heavy irrigation should be located at least 10
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 irrigation.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this area atthis time. V/e make no warranty either express or implied.
The conclusions and recommendations submitted in this re,port 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 c¡nsulted. 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 sxcavati.on is performed. If conditions encountered
during construction appe¡u difflerent 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 clicnt 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 ¡ecommendations, 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.
Resp ectfu lly Sì]bmitted,
Kumar & Associates, fnc.
Steven L. Pawlak, P.E.
Reviewed by:
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Kurnar & A¡¡oclatee, lnc. o Pro¡ect No. 19.7.291
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Daniel E. Hardin, P.E.
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cc: JohnHowa¡d-(þhnhowardri!:willorvcreekms.com)
Sopris Engineering - Yancy Nichol ()¡ni chol @sopri sen g. com)
Oddo Engineering-Bob Oddo @
Kumar & Associatee, lnc. e Proloct No. l9-7-291
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