HomeMy WebLinkAboutSubsoil Study for Foundation Design 02.21.18t:lj -- ;j.r"w iiÍru Nif Ai.:¡5020 County Road 154
Glenwood Springs, C0 81601
Phone: (970) e45"7988
Fax (e70) e45"8454
Email: hpkglenwood@kumarusa.com
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Office Locaiions: Denver (HQ), Parket Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado
SUtsSOil, STUÐY
r.OR. F'OUNÐ,{T'IOIq DESNGN
M{.OT'ÛSEÐ RESTÐEI{CE
r,clT' f"o, PEACH VA[,Ï,EY AARES
T'tsÐ COUNTY trTOA.Ð 2N4
G.åR.TINE[,D CTUNT'Y, CûI-TRAÐC}
JOts N0.1.8-7-1.39
F]EtsRUA.RV 2X.,20X8
P]ITEPAR]OD ]FOR.:
NruCTTABT, MT'I,]LO
896 COUN1IY R.OAD 266
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PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS
FIELD ÐPLORATION
ST]BSURFACE CONDMIONS
FOI.INDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS
FOUNDATIONS......,...
FLOOR SLABS
LINDERDRAI}{ SYSTEM
SURFACE DRAINAGE
I-IMITATIONS...,
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORhTGS
FIGT]RE 3 . LI]GENI) AND NOTES
FTGURE 4 _ S\VELL-CONSOLIDATION TEST RESULTS
TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS
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¿* Proiect No. 1 B-7-139
PUP"POSM AIND SCOP]g CI]F S]TINDV
This report presents the results ofa subsoil sfudy for aproposed residence to be located on Lot
10, Peach Valley Acres, TBD County Road 214, Garfield County, Colorado. The projecr site is
shown on Figure 1. The purpose of lhe shtdy was to develop recomrnendations for the
foundation design, The study was conducted in accordance with our proposal for geotechnical
engineering services to Michael Mello dated January 3L,2018.
A field exploration progrâm consisting of exploratory borings was conducted to obtain
info¡mation on the snbsurface conditions. Samples of the subsoiis obtaineil during the field
exploration were tested in the laboratory to detemine their classification, cornpressibilit-y or
swell and other engineering characterisfics. The resuìts of the field exploration and laboratory
testing were analyzed [o develop recorffnendations for founclation ty¡res, depths and allowable
plessures for the proposed building foundation. This report summarjzes the data obtained during
this study and presents our conclusions, design t'ccommcnclations and other geotechnical
engineering considerations based on the proposed construction and the subsurface conditions
encountered.
P]R.OPOSED COINST]R.UCIIXOFI
The proposed residence will be a one story wood fi'anr.e stntctnte above a clawlspace and with an
attached garage. Garage floor will be slab*on-grade. Grading for the structure is assumed to be
relatively minor with cut depths between about? to 4 feet. lYe assume relatively light
foundation loadings, typical ofthe proposed type ofconstruction.
Ifbuilding loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recom¡riendations contained in this reporf.
SNT]E CONDNTNONS
The property is 2.0 acres and located to the south of County RoadZl{ ffeach Valley Road) and
on the east side of Peach Lane. The neighbor's gravel driveway lies along the north lot üne.
Vegetation consists of grass and weeds. The ground surface is relatively flat with a slight siope
down to the sonih.
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Projeci No. 1B-7-'139
a
iulEtt,Ð EXPIL()IR Alt 1r())N
The field exploration for the project was condlrcted on February 1, 2018. Two exploraiory
borings werc drilled at the locations shown on Figure I to evaluate the subsuúace conditions.
The borings were advanced with 4 inch diameter continuous flight augers powered by a h'uck-
mounted CME-458 dtill rig- The borings were logged by arepresentative of H-P/I{umar.
Samples of the subsoils were talçen with a 2 rlrch I.D. spoon sampler. The sampler was driven
into the subsoils at vatious 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 vahres are ail indication of the relative density or consistency of the
subsoils. Depths at which the samples were taken and the penctration lesistance values ale
shown on the Logs of Exploratory Borings, Figure 2. The samples wele retul"ned to our
laboratory for review by the ploject engineer and testing.
S [I]ESU]]RTA.C]E CONDITNOTqS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. .Tbe
subsoils, below aboutr/z foot oftopsoil, consist of'about SVzfeetofstiffto very stiff, silty sandy
clay over{ying medium dense to stiff, silty sand and clay down to the maximum explored depth
of3i feet,
Laboratory testing performed on samples obtained from the borings included natural moisture
content, density and finer then sand sÍze gradation anaiyses. Resuhs of swell-consolidation
testing performed on relatively undisturbed drive samples of silty sand and clay, presented on
Figure 4, typically indicate low to moderate complessibility under conditions of loading and
wetting and iow collapse potential (settlement nnder constant load) when wetted. A sample from
Boring 2 at 5 f.eet showed a low expansion potential when wetted. The laboratory testïng is
srjmmarized in Table 1.
Free water was not encountered in the borin-qs at the time of drilling. 'When checlced 4 days later,
tlre f¡ee watcr levcl in Boring 1 rvas at 2ilVzfectin dcpth. The subsoils were slightly rnoist to wet
bølow gr"oundwater level.
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Project No. 16-7-1il9
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FOUNIT}A.TIOIV BEAR]INI-G CONDNTIOINS
The silty sand and clay soils encountered in the boring possess low bearing capacity and, from
our experience in the area, typically tend to compress when they become wetted. Lightly loaded
spread footings shot¡ld be feasible for foundation support of thc residence with some risk of
illovement. The risk of movement is primarily if the bearing soils were to becomc wetted and
precautions should be taken to prevent wetting, Sources of wetfing inclucle excessive inigation
near the foundation, poor surface drainage adjacent {.o foundation walls and utility line leaks.
The excavation should be observed by a representative of the geotechnical engineer. Any
expansive clay soils encountcreci at bearing levcl in the excavation should bc reniovecl anrl
replaced by compacted structural fill.
]DESNGN RECOMNffihID^ATIO¡{S
FOLINDATIONS
Considering the subsurface conditions encountered in tJre exploratory borings and the nature of
the proposed construction, we recomrnend the buildingbe founded with spread footings bearing
on the natural soils olcompacted structu¡al fill.
The design and construction cdteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils or compacted struchlral fill
should be designed for an allowable bearing pressure of i,500 psf. Based on
experience, we expect initial settlement of footings designed and constructed as
discussed in this section will be about 1 inch or less. There could be additional
movemcnt if the bearing soils become wetted of about t/zto l inch depending on
the depth and extent of the wetting.
2) The footings should baye aminimum widrh of 18 inches for continuous walls and
2 feet for isolated Pads.
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Exterior footings and footings beneath unheated areas should bc provided with
adequate soil cover above their be¿ujag elevation for frost protection. Placement
of foundations at least 36 inches below exterior grade is typically used in this
afea.
Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at lcast 14 feet.
Foundation walls acting as retaining strucfures should also be designed to resist a
lateral earth pressnre coûesponding to an equivalent fluid nnit weight of at least
50 pcf.
The topsoil, expansive clay soils and any loose or disturbed soils should be
removed from thc building area and rcplaced with shuctural Íill oL the footing
bearing level extended down to the nah¡ral soils, The exposed soils in footing
area should then be moistened and compacted. Structural fili below footing grade
should consist of irnported 3/a-arch.road base compacted to at least 98Vo c:t Llle-
¡n¿rximunl standard Proctor density at a moisture content ncar optirnum.
A representative of the geotechnical engineer should obsgrve all footing
excavalions prior to concrete placement to evaluate bearing conditions.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade
construction. Expansive clay soils shouldbe removed and can be replaced with compacted
structui'al fill. To reduce the effects of some differential movement, floor slabs should be
separated from all bearing walls and columns with expansion joints which a1low unrestrained
vertical movement, Floor slab cont¡ol joints should be used to reduce damagc due to shrinkage
claclting. Thc rcquiremcnfs frrr joint spacing and slab reinfoLceme,nt slrould be estalrlishctl l.ry thc
designer based on experience and the intended slab use. A minimum 4 inch layer of free-
draining gravel should be placed beneath slabs to faciJttaÍe drainage. This material should
consist of minus 2 inch aggregate with at least 507o retained on the No. 4 sieve and less thaoZTa
passing the No, 200 sieve.
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Project f",to. 1B-7-139
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All fi,li materials for support of floor slabs should be òompacted to at least 95Vo of.maximum
standard Proctor density at a moisture content nôar optimum. Required fill can consist of
imported 3/+-inchroad base devoid of vegetation, topsoiì and oversized rock.
I.INDERDRAIN SYSTEM
For the proposed shallow crawlspace and slab-on:grade garage, a foundation drain system is not
required, It has been our experience in the at'ea that local perched groundwater can develop
durÌng times of heavy precþitation or seasonal runoff. Frozen ground during spring mnoff can
also create a perched condition,
'We recommend below-grade construction, such as deep crawlspace (over 4 feet) and retaining
walls, 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
ilrvcrt levcl rvith frce-draining granular ¡nateúal. The drain should be placed at least 1 foot
below lowest adjacent finish grade and sloped at a minimumTTo to a suitable gravity outlet.
Free-draining granular material used in the underdrain system should contain hessthan2To
passing the No. 200 sieve, less than 507o passing l.he No, 4 sieve and have a maximum size of.2
inches. The drain gravel baclcfill should be at least LYzfee't deep.
SURFACE DRAINAGE
Positive surface drainage is a very important aspeci of the project to prevent welting of the
bearing soils. 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 and underslab areas shouldbe avoided
during constrr¡ction.
2) Exterior backfill should be adjLrsted to near optimum moisture and compacted to
at least 957o of the maximum standard P¡octor density in pavement and slab ar¿as
and to at least 90Vo 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 fromthe foundation in a-11 directions. .We recommend a minimum
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Project Nlo. 18-7-139
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slope of 12 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-dlaining w¿Lll backfiil shouid be
covered with filter fabric and capped with about 2 feær of the on-site soiis to
reduce surface water infiltration.
Roof downspouts and drains shor.rld discharge well beyond the limits of all
baclcfill.
Landscaping which requires regular heavy irrigation should be located at least 10
feet fi'om foundation walls. Consideration should be given to use of xeriscape to
reduce the potontial for wetting of soils bclow thc building caused by irigation.
I,]IÞflru'AT'TONIS
This study has becn conducted in accordance with generally accepted geotechnical engineering
princþles and practices in this atea atthis time. We make no wananty either exp.ress or implied.
The conclusions and recommendations submitted in this reporl are based upon the data obtainerl
from thç exploratory borings drilled at the locations jndicated on Figure 1, the proposed ty¡re 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 ftiture. 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 ai the exploratory borings and variations in the subsurface
conditions may not become evident until excavation is performed. If conditions encountered
during construction appear different f,'om those described in this report, we should be notified so
thãt re-evaluation of the recommendations may be made.
This reporl has been prepared for the exclusive use by our client for design purposes. 'We are not
responsible for technical interpretations by others of our i¡formation. As the project evolves, rre
should provide continued consultation and. fielcl services during construction to review and
monitor the ímplementation of our recofnmendations, and to verify that the recommendations
have been appropriately interpreted. Significant design changes may requiie additional analysis
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Prcjeci I\¡o. 18-7-'139
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or modifioations to the tecommendationí presented herein. \ile reco'rnmend on-site observation
of oxcavations and foundation bearing strata and testing of structural f,l1by a representative of
the geotechnical engineer.
Respectfu ily Submitted,
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Shane M. Mello, Staff Engineer
Reviewedby:''-i,'::: !:.a
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Daniel E.IIardin, P
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Froiect trlo. 18-7-] 39
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ilg. ITOCATION OF EXPLORATORY BORINGSH-PryKUI\IIAR1 B-7* 1 39
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EORING 1 BORING .2
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12/ 12
14/ 12
WC=6.8
DD=1 1 3
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16/12
WC=6.'6
DD=1 04
20/ 12
WC=8.7
DD=1 14
22/ 12
s/12
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31 /12
WC=8.5
DD=1 1 7
I zs/tz' WC=6.4
DD=116
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WC=7.3
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23
30
55
22/2
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25
50
55
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DD=112
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Fig, 2LOGS OF EXPLORATORY BORINGSH-PæßruFWAR
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ffiqEND
TOPSOIL; ORGANIC SILTY SANDY CLAY, FIRM, MOISI, DARK BROWN.
CLAY (CL); SILTY, SANDY, STIFF To VERY STIFF, SLIGHTLY MolST, BROWN
SILTY,. MEOIUM DENsE, SLIGHTLY MOIST TO WET,
RELATIVELY UNDISTURBED DRIVE SAMPIE; 2-INCH l.D. OALIFoRNIA LINER SAMPLE.
12/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 12 BLOWS OF A 140_POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE CALIFORNIA OR SPT SAMPLER 12 INCHES.
4 OEPTH To WATER LEVEL AND NUMBER OF DAYS AFTER DRILLING MEASUREMENT WAS MADE.
.-+= DEPTH ÀT WHICH BORING CAVED FOLLOWING DRILLING
NOTES
THE EXPLORATORY EORINGS WERE DRILTED ON TETRUANY 1,2018 WITII A 4-INC[.I 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.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY BORINGS ARE PLOTTED TO DEPTH.
4, THE EXPLORATORY EORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE
DEGREE IMPLIED BY THE METHOD USED:
5. THE LINES BETWEEN MATERIALS SHOWN ON THË EXPLORATORY EORING LOGS REPRESENT THE
APPROXIMATE BOUNÐARIES BETWEEN MATERIAL TYPES AND THE TRAN5ITIONS MÀY BE GRADUAL.
6. GROUNDWATER LEVEL SHOWN ON THE LOG WAS MEASURED AT THE TIME AND UNDER
CONDITION5 INDICATED. FLUCTUATIONS IN THE WATER LEVEL MAY OCCUR WITH TIME.
7. LABORATORY TEST RESULTS;
WC = WATER CONTEI-IT (%) (ASTM D 2216);
DD = DRY DENSTTY (pct) (aSrU t 2216);
*2OOA PERCENTAGE PÄSSING NO. 2OO SIEVE (ASTM D 1r40)
m
SAND AND CLAY
LÍGHT BROWN TO
(sc-cr-);
BROWN.
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SAIVIPLE OF: Silty Sand ond Clo¡'
FROlvl; Boring 1 @ 10'
Wc = 6.6 i4, DD = 104 pcf
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ADDITIONÂL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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- KSF 10 It.0
SAþIPLE OF: Silty Sond ond CloY
FROlrl:Boring2ica5'
WC = 6,4 id, DD = 116 pcf
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APPLIED PRESSURE - KSF l0
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Fig, z¡SWTLL_CONSOLIDATIOhI TEST RESULTSH:PryIruIVilAR18-7 -139
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SLÛItflNÎß\RV OF [-rS[3ORfa\TORY T EST [REStrll-TS
Project No. 18-7-'{39
DEPTH
(ft)
NATURAL
MOISTURE
CONTENT
NATURAL GRADATIqN
DRY GRAVEL SAND-DENslrY (9.i) (ri,)
(ncfj
PERCENT
PASSING
NO.200
SIEVE
UNCONFINED
COMPRESS¡VE
STRENGTHBORING
I
I
ONSAMPLE
(9;)IP.qFì
ATTERBËRG LIMITS I
Lreuro rusttc I
LIMIT i INDEX
lo,'"\ \ ri/"\
SOIL ryPE
I ó.+
10
(r.8
Ò-t)
113
1 {)r.I Silt-r Sand and Cia¡'
SiltY SandY Clâ1
15 I
I Silb'Sand and Cla1'11"1
I 1Iit
i Sil['Sand¡'Cla1
l1{;5
.ì/ì
1
(i.-f
7.3
Silty Sand and Ciay
Sill-v Sand anci Cla¡,