HomeMy WebLinkAboutSubsoils Report for Foundation DesignI(+rt Kumar & Associates, lnc.@
Geotechnical and Materials Engineers 5020 Counûy'tscod 154
and Environmental Scientìsts Glenwood SpringE"€OEt60l
phone: (9ffi))94.Í7988
ìa* (97@94s84s4
ernail : ka g lenwoodf@lomørrusa-com
An Employ¡t owncd compony www.kuma¡usa.com
Oflìce Locations: Donver (HQ), Parker, Colorado Springs, Fort Collins, Glenr.vood Springs, and SummitC-ønt$Cblorado
%SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 3, RUIZ SOUTH MINOR SUBDTWSION
COUNTY ROAD 33I
GARFIELD COUNTY, COLOR-{DO
PROJECT NO.20-7-555
NOVEMBER 20,2020
PRI,PARED FOR:
SAM RUIZ
P.O. BOX 456
SILT, COLORADO 81652
nce@,q.com
TABLE OF CONTtrNTS
PURPOSE AND SCOPE OF STUDY ....
PROPOSED CONSTRLTCTION
SITE CONDITTONS
FIELD EXPLORATION .......
SUBSURFACE CONDITIONS
FOTINDATION BEARTNG CONDITIONS
DESIGN RECOMMENDATIONS
FOI'NDATIONS
FOI.INDATION AND RETAINING WALLS
FLOOR SLABS
UNDERDRAIN SYSTEM
SURFACE DRAINAGE...
LlMTTATIONS
FIGURE 1 . LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGF,ND AND NOTES
TABLE I. SUMMARY OF LABORATORY TEST RESULTS
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PURPOSE AND SCOPE OF STUDY
This report presents the results of a strbsoil study for a proposed residence to be located on Lot 3,
Ruiz South Minor subdivision, County Road 331, Garfield County, Colorado. The pmject site is
shown on Figure 1. The purpose of the sfucly was to clevelop recommendations for the
foundation design. The study was conducted in accordance with our agreement for geotechnical
engineering seruices to Sam Ruiz dated September 25,202{J.
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 detçrmine their classification and other engineering
characteristics. The results of the field exploration and laboratory testing were aualyzed to
develop rccommendations for foundation types, depths and allowable pressnres fot the proposed
br"rilding foundation. This report surnmarizes the data obtained during this study and presents our
conclusions, design recornmendations and other geotechnical engineering considerations based
on the proposed construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
Development plans for the lot,uvere conceptnal at the tirne of our study. In general, the proposecl
residence will be a single-story structure with an attached garage. There could be a basement
below part of the residence. Ground floor will be stntcttiral above crawlspace for the living area
ancl slab-on-grade f'or the galage and basement if constructed. Gracling for the structure is
assumed to be relarively minor with cut depths between about 2 to 4 feet. We assume relatively
light loundation 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 building site is in the central part of the lot on top of a hill as shown by the contour lines on
Figure 1. The gtound surface across the building area is rnoderately sloping rvith around 8 feet
of elevation difference. Cobble and boulder size rock fragments are exposed on the ground
surface. Vegetation consists of grass, weeds and cactus.
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FIELD EXPLORATION
The field exploration for the project was conducted on C)ctober 1,202A. Two exploratory
borings were drilled at the locations shown on Figure I to er.aluate the subsurface conditions.
Tl.e borings were aclvanced with 4-inch cliameter continuous flight augers powereri by a tnrck-
mountecl CME-458 drill rig. The borings were iogged by a representative of Kumar &
Associates, Inc.
Samples of the subsurface materials were taken with 1% inch ancl 2-inch I.D. spoon sanrplers.
The samplers rvere driven into the subsurface materials at various depths with blorvs from a 140
polmd hamrner falling 30 inches, This test is sirnilar to the standard penetration test described by
ASTM Method D-1586. The penehation resistance values are an indication of the relative
density or consistency of the subsoils and hardness of the bedrock. Depths at which the samples
were taken and the penetration resistance values are shown on the Logs of Exploratory Boriugs,
Figure 2. The samples were returnecl to our laboratory tbr review by the project engineer and
testing.
SUBSTJRFACD CONDITIONS
Glaphic logs of the subsudäce conditions encountered at the site are shown on Figure 2. The
subsoils encouatered, below a thin topsoil layer, consist of weathered siltstone/claystone or very
stiff to hard sandy clay down tc around 4 feet overlying very hard siltstonelsanclstone beclrock to
the boring depths of 16 to 20 feet.
Laboratory testing performed on samples obtained frorn the borings included natural moisfure
conlent and density, finer than sand size gradation analyses and liquid and plastic limits. The
laboratory testing is summarizecl in Table 1.
No free water w'as enconntered in the borings at the time of drilling and the subsoils were
typically moist.
FOUNDATION BEARING CONDITIONS
The upper clay soils and rveather bedrock are very stitTto hard and appear suitable for support of
lightly loaded spread footings r,vith low movement potential, mainly if the bearing soils are
rvetted. Some of the soils o¡ weathcred bcdrock may cxhibit cxpansion potentisl when lvettecl
and should tre further evaluated for footing heave risk at the time of excavation. The underlying
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siltstonelsandstone bedrock should have minor settlementiheave potenti¿i under loading and
wetting conditions.
DESIGN RECOM]\{E NDATIONS
FOUNDATIONS
Considering the subsulface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recotnmend the building be fbunded with spread tbotings bealing
on the natural bedrock materials.
The design and construction criteda presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural bedrock materials should be designed
for an allowable bearing pressure of 2,500 psf. Based on experience, we expect
settlernent of tbotings designed and constructed as discussed in this section will
be about 1 inch or less. There could be potential for post-construction movement
up to around I inc.h clepending on the bearing materials.
2) The footings should have a minimum width of 16 irches for continuous walls and
2 fee¿ for isolated pads.
3) Exterior tbotings 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 fypically used in this
area.
4) Continuous foundation walls should be heavily reinf'orced top and bottom to span
Iocal anomalies such as by assurning an unsupported length of at leasl 14 feet.
Foundation walls acting as retaining stmcfures should also be designed to resist
lateral earth pressures as discussed in the "Foutrdation and Retaining Walls"
section of this rePort.
5) The topsoil and any loose or distulbecl soils should be removed and the footing
bearing level extended down to the undisturbed natural bedrock nraterials. fte
exposed soils in footing area should then be moistened and compacted.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
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FOLINDATION AND RETAINING }YALLS
Foundation rvalls and retaining structures which are laterally supported and can be expected to
undergo only a slight amount of deflection should be designed tbr a lateral ezuth pressure
computed on the basis of an equivalent fluid unit weight of at lcast 55 pcf for backfill consisting
of the on-site fìne-grained soils arrd well broken bedrock. Cantileverecl retaining struchrres
which are separste from the residence and can be expected to deflect sufficiently to mobilizc the
ftill actíve earth pressure condition should be designed for a lateral earth pressure computecl on
the basis of an equivalent fluid unit weight of at least 45 pcf for backfill consisting of the on-site
f,rne-grained soils and *'el1 broken bedrock materials.
All foundation and retaining structures should be designed tbr appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction materials and equipment.
The pressures recommended above assulne drained conditions behind the walls and a horizontal
backtill 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
shoulcl tre provided tu prevent hytlrustal.ic,pressure builtlup behintl walls.
Backfill should be placed in uniform lifts and compacted fo at least 90% of the maximum
standard Proctor clensity at neal optimum moisture content. Backfill placed in pavement and
walkway areas should be compacted to at least95Yo of the maximum standard Proctor density.
Care should be taken not to overcompact the backfill or use large equiprnent near the wall, since
this could cause excessive lateral pressure on the wall. Sorne settlement of deep fbunclation wall
backfill should be expectetl, even if the material is placed coffsLìtly. and could result in distress to
facilities constructed on the b¿ckfrll. Backfill should not contaiu organics, debris or rock larger
than abuut 6 inches.
The lateral resistance of foundation or retaining r,vall footings will be a combination of the
sliding resistance of the footing on the foundation materials and passive earth pressure against
the sicle of the footing. Resistance to sliding at the bottoms of the footings can be calculated
based on a coef'ficient of friction of 0.40. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalenT fluid unit weight of 375 pcf. The
coefficient of friction and passive prossure values recommended above assume ultimate soil
strength. Suitable factors of safet¡r should be includecl in the clesign to lirrit the strain whìch will
occtr at the ultimate strength, particularly in the case of passive resistance, I.'ill placed against
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the sides of the footings to resist lateral loads should be cornpacted to at least 95% of the
rnaximurn standarcl Proctor density at a moisture content near optimutn.
FLOOR SLABS
The natu¡al on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade
consfruction with low movement potential. The expansion potential of the exposed materials
should be evaluated at the tirne of excavation. To rednce the effects of some tlifferenti¿l
movement, floor slabs shoulcl be separated from all bearing walls and colurnns with expansion
joints which allow unrestrained yertical movernent. 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 basecl on experience and the intended slab
use. A minimum 4-inch layer of relatively well graded sand and gtavel such as base course
should be placed beneath interior slabs for subgrade support. This material should consist of
minus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less than 12% passing
the No. 200 sieve. Below basement floor slab, the under slab gravel should be relatively free
draining and consist of minus 2-inch aggregate with at Ieast SAYa retained on the No. 4 sieve ancl
less than 2% passing the No. 200 sieve.
All iìIl materials for support of floor slabs should be compacte<l to at least 95% of maxtmum
standard Proctor density at a moisture content near optimunt. Required fi11 can consist of the on-
site soils dev¡:id of vegetation, topsoil and oversized rock.
LINDERDRATN SYSTEM
Although fi'ee water was not encountered during our exploration, it has been our experience in
the area and where bedrock is shallow that local perched grountlwater can clevelop during tirnes
of heavy precipitation or seasollal runoff. Frozen ground during spring runoff cau create a
perched condition. We reçommend below-grade construction, such as retaining walls,
crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by
an underclrain system. Relatively shallow crawlspaces may not need an underdrain providecl the
backfill is well compacted and the surface is adequately sloped to drain away from the
foundation.
Where al underdrain is provided, it should consist of drainpipe placed in the bottom of the wall
backfill surrounded above the invert level witli fiee-draining granular material. The drain should
be placed at each level of excavation and at least 1 fbot below lowest atljacent finish gracle and
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sloped at a minimum 10,6 to a suitable gravity outlet. Free-draining granular material 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 shoulcl be at
least I% feet deep.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been cornpleted:
1) Inundatiol of the lbuldation excavations and rurderslab areas should be avoicled
during construction.
2) Extcrior backfill should bc adjustcd to ncar optimum rnoisturc ancl compactcd to
at least 95o/o of the maximum standard Proctor density in pavement and slab areas
and to at least 90% of the maxirnum standard Proctor density in landscape aleas.
3) The ground surface sunounding 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 fìrst 1[) feet in unpaved areas anrl a minimum slope of
3 inches in the first 10 t'eet in paved areas. Free-draining wall backtìll should be
covered with filter fabric and capped rvith about 2 feet of the on-site soils to
reduce surface water intìltration.
4) Roof downspouts and drains should discharge well beyond the iimits of all
backfill.
5) Landsoaping which requires regular heavy inigation should be located at least
5 fèet from foundation walls. Consideration slrould be given to use of xeriscape
to reduce the potential for r,vetting of soils below the building caused by irigation.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles ancl practices in this area at this time. We make no wananty either express or impliecl.
The conclusions and recommendations sr¡bmitted in this report are based upon the data obtained
fiom the exploratory borings drilled at the locations indicated on Figure l, the proposed type of
construction and our experience in the area. Our seruices do not include determining the
presence, prevention or possibility of mold or other biological contaminants {MOBC) developin-e
in the future. lf the client is concerned about MOBC, then a professional in this special field of
practici: should hc consnltcrl. Our finclings inclucle interpolation ancl extrapoìation of thcr
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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 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 {ield 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.
Respectfu lly Submitted,
Kurnsr &. Á.ssociates, lnc.
Steven L. Pawlak, P.E.
Reviewed by:
t
Daniel E. Hardin, P.E.
SLPlkac
Cc: High Country Engineering * Tom Scott (!l-s@bgg1ggqlq)
,i
(t,15222
Kumar & Associates, lnc. i'Project N0,20-7-555