HomeMy WebLinkAboutSubsoil StudylGA$Jrr*;ffiffii'iy*-*
Àn fmdoytt Chr-nod CompcnY
5020 County Road 154
Glenrvood Springs, CO fì1601
phone: (970) 945-7988
fäx: (970) 945-8454
emai I : kaglenivood(l)kumarusa.com
rvlvrv.litrm atusa.cotn
Ol'Tìce Localio¡s: Denver (lIQ), Parker, Cololado Springs. Fort Collins, Glenwoocl Springs, and Sttmrnit County, Cololado
August 14,2020
Victoria Stulgis
220 Harmony Lane
Carbondale, Colorado 8l 623
victoria.stulgis@ gmail.com
RECEIVED
:..'
GARFIELD COUT{TY
. Golrèl ulqÐf usvE&$Pffi f; $TProject No.20-7-358
Subject: Subsoil Study for Foundation Design, Proposed Residence, South of
181 Harmony Lane, Missouri Heights, Garfield County, Colorado
Dear Victoria:
As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations at
the subject site. The study was conducted in accordance with our agreement for geotechnical
engineering services to you dated June 18,2020. The data obtained and our recommendations
based on the proposed construction and subsurface conditions encountered are presented in this
repoft.
Proposed Construction: The proposed residence is assumed to be a one to two story structure
with attached garage located in the a.rea of the site outlined as the building envelope on Figure l.
Ground floors are assumed to be structural over crawlspace for the living areas and slab-on-grade
for the garage. Cut depths are expected to range between about 2 to 6 feet. Foundation loadings
for this type of construction are assumed to be relatively light and typical of the proposed type of
construction.
If building conditions or foundation loadings are significantly different from those described
above, we should be notified to re-evaluate the recommendations presented in this report.
Subsidence Potential: Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the
site. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with
some massive beds of gypsum and limestone. There is a possibility that massive gypsum
deposits associated with the Eagle Valley Evaporite unclerlie portions of the lot. Dissolution of
the gypsum under certain conditions can cause sinkholes to develop and can produce areas of
localized subsidence. During previous work in the area, sinkholes have been observed scattered
throughout the lower Roaring Fork Valley. These sinkholes appear similar to others associated
with the Eagle Valley Evaporite in the area.
Sinkholes were not observed in the immecliate area of the suhject lot. No evidence of cavities
was encountered in the subsurface materials; however, the exploratory pits were relatively
shallow, for foundation design only. Based on our present knowledge of the subsurface
conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of
a
future ground subsidence on this site throughout the service life ofthe proposed residence, in our
opinion, is low; however, the owner should be made aware of the potential for sinkhole
develtlpment. If further investigation of possible cavities in the bedrock below the site is desired,
we should be contacted.
Site Conditions: The subject site was vacant at the time of our field investigation. 'l'he ground
surface is gcntly to moderately sloping clown to the south at grades of between 5 to 20 percent.
Vegetation consists of grass, weeds, sage brush and juniper.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
2 exploratory pits in the residence area and 2 profile pits in the septic field area at the
approximate locations shown on Figure l. The logs of the pits are presented on Figure 2. The
subsoils encountered, below about 1 to I%feet of topsoil, consist of cemented caliche with basalt
cobbles and scattered boulders to the maximum explorecl depth of 3Yz feet. The subsoils
encountered in the residence pits and septic field profile pits were similar across the site. Results
of a gradation analysis performed on a sample of cemented caliche (minus 3-inch fraction)
obtained from the site are presented on Figure 3. No free water was observed in the pits at the
timc of excavation and the soils were slightly moist.
Foundation Rccommendations: Considering the subsoil conclitions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
placed on the undisturbed natural soil designed for an allowable soil bearing pressure of 2,000
psf for support of the proposed residence. The soils tend to compress after wetting and there
coulcl be some post-construction foundation settlement. Footings should be a minir¡u¡r wiclth of
16 inches for continuous walls and 2 feet for columns. Loose and disturbed soils encountered at
the foundation bearing level within the excavation should be removed and the footing bearing
level extended down to the undisturbed natural soils. Large basalt cobbles and basalt boulders
will likely be encountered in the foundation excavation. Exterior footings should be provided
with adequate cover above their bearing elevations for frost protection. Placement of footings at
least 36 inches below the exterior grade is typically used in this area. Continuous foundation
walls should be reinforced top anel bottom to span loca! anomalies such as b5r assuming an
unsupported length of at least 12 feet. Foundation walls acting as retaining structures should be
designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least
50 pcf for the on-site soil as backfill.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly to
moderately 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
reducc damage due to shrinkage craoking. The requirements for joint spacing and slab
reinforcement should be established by the designer based on experience and the intenclecl slab
use. A minimum 4 inch layer of free-draining gravel should be placed beneath basement level
Kumar & Associates, lnc. o Project No. 20.7.358
-3-
slabs to facilitate drainage. This material should consist of minus 2-tnch aggregate with less than
507o passing the No. 4 sieve and less than2Yo passing the No' 200 sieve.
All fill materials for support of floor slabs should be compacted to at least95o/o of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site soils or a suitable imported material such as 'A-inch road base devoid of vegetation, topsoil
and oversized rock.
Underdrain System: Although free water was not encountered during our exploration, it has
been our experience in the areathat local perched groundwater can develop during times of
heavy precipitation or seasonal runoíf. Frozen ground during spring runoffcan also create a
perched condition. We recommend below-grade construction, such as retaining walls,
crawlspace and basement areas (if any), be protected from wetting and hydrostatic pressure
buildup by an underdrain system.
The drains should consist of drainpipe placed in the bottom of the wallbackfill surrounded above
the invert level with free-draining granular material. The drain should be placed at each level of
excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum lYoto
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2Yo passingthe 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 lVzfeet deep.
Surface I)rainage: 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 should be avoided
during construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95%;o of the maximum standard Proctor density in pavement and slab areas
and to at least 90%o of the maximum standard Proctor density in landscape areas.
Free-draining wall backfill should be capped with about 2 feet of the on-site,
finer-graded soils to reduce surface water infiltration.
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 12 inches in the frrst l0 feet in unpaved areas and a minimum slope of
3 inches in the frrst 10 feet in pavement and walkway areas. A swale may be
needed uphill to direct surface runoff around the residence.
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 the building. Consideration should be given to the use of xeriscape
to limit potential wetting of soils below the foundation caused by irrigation.
Kumar & Associates, lnc.6 Project No. 20-7-358
-4-
I"ÍmÍtations; This study has been cnnductçcl in accordance with generally accçted geotechnical
engineoriüg principles *nd practices in this area at this tjme. IVe mske no warranty either
exprëss or implied. The eonclusicns and recommenrJations submitted in this re,port are haspd
upan the data r:btainetl fnrrn the exploratory pits excavated at the locations indicated on Figure I
and to the depths show¡r on Figure 2, the proposed type of construction, arld our experience in
tlie area. Our services do not include determining the presenc*, preventiçn or possibility of mold
or other biological contaminants (MOBC) developi¡g i11 the future. If the client is concerned
¿bout MGBC, then a professi*nal in this special field of practice should be cernsulted. Our
findings inciude interpolation and extrapolation cf the subsurface cantlitions identified at the
cxploratory pits and variations in the subswtbce conditions may not become evident until
excavetion is performed' If conditions encountered during constructioü âppear diffçrent &om
thosc describsd in thís report, r¡'e should bç notified at once so re-evaluation of the
recommendations may be made.
This report has been prepared far tlie exclusive use hy CIur client fbr design purpCIses. Sy'e are not
responsible for technic*l interpretations by others of our informafion. As the prcject evolves, we
should provide cantinued consultation snd fielcl services during construction to review and
monitor the implernentntian of *ur recommendations, and to verify that the recommendatians
have been appropriately interpreted. Signiñcnnt dssign clurrges gray require nrtditional analysis
or mc¡difications to the recommendations prese,trted herein. 'lç'e recornrnend on-site observation
of excavations and fbr.lndatian bea*ng sfrata and testing of struütural fill by a representative cf
the geotechnical engineer.
If you have any questions ar if we may be af further nssistance, please let us know
Respsctfu lly Submitted,
K*xm*r E¿ Açs*c[steso lË**.
Tnrrrec É{ Fqrenne Ë Ià -. a r{ çvÀ¡u, &.¿r
Reviewed by:
Daniel E.
JHP/kac
aftachments
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Figure
Figure
Fits
2 Fits
Figure 3 * Cradaticn Test Results
Table 1 * Sumnrary c¡f Laboratory Test Results
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APPROXIMATE SCALE-FEET
20-7 -358 Kumar & Associates LOCATION OF EXPLORATORY & PROFILE PITS Fig. 1
E
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PIT 1
EL.117'
PIT 2
1
PP- 1
EL. 1 05'
PP_2
EL. 1 00'EL.
t-l¡l
t¡J
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I
It-fLl¡lô
0
5
I WC=11.8
{.4=67
-2O0=17
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0
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¡I WC= I 0.4
DD=86
LEGEND
ToPSolL; SAND, SILTY To vERy stLTy, oRcANtcs, F|RM, sLtcHTLy Motsr, RED BRowN.
ÇALICHE: CEMENTED, BASALT COBBLES AND SCATTERED BOULDERS, SANDY, SLIGHTLY MOIST,PALE TAN.
DISTURBED BULK SAMPLE.
I PRACTICAL REFUSAL TO EXCAVATION
NOTES
t
2.
5.
4.
5.
6.
7.
THE EXPLORATORY PITS WERE EXCAVATED ON JULY 1, 2O2O WITH A TRACKEDMINI-EXCAVATOR.
THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROMFEATURES SHOWN ON THE SITE PLAN PROVIDED.
THE ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL AND REFER TOPROFILE PIT 2 AS 1OO" ASSUMED.
THE EXI'LORATORY PIT LOCATIONS AND ELEVATIONS SHOULI, Bt CONSIDERED ACCURATE ONLYTO THE DEGREE IMPLIED BY THE METHOD USED.
THF llNFs RrTwtrFN \/^TtrÞt^t Q Qur'ìr^rrt ^rt lur Fvır ^ñ^?^ñvr! r r rL L^r LvñA t và r Til LvreJ NLf KLJLN I l llLAPPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WEREBACKFILLEÐ SUBSEQUENT TO SAMPLING.
LABORATORY TEST RESULTS:wc = wATER CONTENT (%) (ASTM D 2216);DD = DRY DENSTTY (pcr) (lsrv D 2216);+4 = pERCENTAGE RETATNED ON NO. 4 STEVE (ASTM D a22);
-2OO= PERCENTAGE pASStNc NO. 200 STEVE (ASTM D 1140).
20-7-358 Kumar & Associates LOGS OF EXPLORATORY PITS Fis, 2
HYDROMETER ANALYSIS SIEVE ANALYSIS
ltrE nilDtxôs
2,t HRS 7 HRS utN al
U.S. SANDARO SERIES CLEAR SQUARE OFENIT{OS
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SAND GRAVEL
FINE MEDIUM COARSE FINE COARSE
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DIAMETER OF IN
CLAY TO SILT COBBLES
GRAVEL 67 % SAND 16 %
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Cem€ntod Collche wlth Bosoll Grovel
SILT AND CLAY 17 %
FROM: Pll 1 O 2' lo 2.5'
Thrt. t.!l rcrull! cpply only lo lh.
!ompl!! whlch warr l.!|.d, fh!
llrllng roporl rhqll nol b! ruproducrd.
cxccpt ln lull, wllhoul lhc wrlllcn
opprcvol of Kumor & Alloclol€, lno.
Sicvc qnoly¡l¡ lltllng ls parfom.d ln
qccordoncc wllh AsÏM D69t5, ASTM D7928,
ASTM Cl56 ond,/or ASTM Dll,l0,
20-7-358 Kumar & Associates GRADATION TEST RESULTS Fis. 5
KhnlÍu¡mr û Assaciateg l*¡. 6Gectechnical and håateriais Engineersand Envirsnmenlaj $cientislsTABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.20.7.358Cemented C¿liche withBasalt GravelSOIL TYPEUNCONFINEDCOMPRESSIVESTRENGTHVery Gravelly Silty Sand(olPLASTICINDEXATTERBERG LIMITS{%)LIQUID LIMITPERCENfPASST,IG NO.200 stElE7I61SAND%tGRADATION(%)GRAVEL67NATURALMOISTURECONTENTNATURALDRYDENSITY86l 1.810.4DEPTHPfr2%JSAMPLE LOCATIONIProfilePit2