HomeMy WebLinkAboutSubsoil Study for Foundation Design 03.18.2020l(+lliffiiffi,ffi;$'ä-"
An Employcc ot¡ncd Compony
5020 County Ro¡d 154
Glenwood Springs" CO 8t6CI1
phone: (970) 945-7988
fa* (970) 945-8454
email : kaglcnwood@kumarusa.com
wwrv.lcumanlsa.com
Offica Locations : Dowa (ftQ) Pa*cq Colondo Spings, Fort Collins, Glenuood Springs, and Sunmit Comty, Colorado
ST]BSOIL STT]DY
FOR F'OUNDATION DESIGN
PROPOSED RESIDENCE AND BARN
BURRY RANCH
9155 HIGHWAY 82
GARFIELD COI]NTY, COLORADO
PROJECT NO.20-7-147
MARCH I8,2O2O
PREPARED FOR:
MICHALEEN Ai{D MICHAEL JEROMMUS
1012 13TfI STREET
GOLDEN, COLORADO 80401
maieronim us@ sm ail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY..............
PROPOSED CONSTRUCTION
SITE CONDITIONS......
SUBSIDENCE POTENTIAL..........
FIELD EXPLORATION
SUBSURFACE CONDITIONS
FOTINDATION BEARTNG CONDITIONS .....
DESIGN RECOMMENDATION S
FOUNDATIONS .........
FLOOR SLABS
UNDERDRAIN SYSTEM ........
SURFACE DRAINAGE
LrMITATrONS.................
FIGURE 1 . LOCATION OF E)GLORATORY BORINGS
FTGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS
FIGURE 5 . GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
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Kumar t Aseochtgs, lltc. ¡Ptoiect llo. ãl-7-1{7
PUR}OSE AND SCOPE OF STTJDY
This report presents the results of a subsoil study for a proposed residence and barn to be located
on Burry Ranch, at 9155 Highway 82, Garfield 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 accordance with our proposal for geotechnical engineering services
to Michaleen and Michael Jeronimus dated February 12,2020.
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 dctermine 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 foundations. 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 subsurface conditions
encountered.
PROPOSED CONSTRUCTION
The proposed residence will be a two-story wood frame structure with att¿ched garage. The
proposed barn is assumed to be a two story structure with accessory dwelling unit on the upper
level. Ground floors are assumed to be structural over crawlspace for the residence and slab-on-
grade for the garage and bam. Grading for the structure is assumed to be relatively minor with
cut depths between about 2 to 5 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 recommendations contained in this report.
SITE CONDITIONS
The subject site was vacant at the time of our field exploration. The ground surface is sloping
gently down to the west at grades between 2 and 4 percent. Elevation difference across the
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proposed house location is about 3 feet and across the proposed barn location is about Yzfoot.
The Roaring Fork River is to the west and south about l0 feet below the proposed house
elevation.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the subject site. These rocks
¡re 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 underlie portions of the lot. Dissolution of the gypsum under certain
conditions can cause sinkholes to develop and can produce areas oflocalized subsidence.
During previous work in the area, several sinkholes were observed scattered throughout the
Carbondale and Aspen Glen areas. These sinkholes appear similar to others associated with the
Eagle Valley Evaporite in areas of the Eagle Valley.
Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities
was encountered in the subsurface materials; however, the exploratory borings 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
future ground subsidence on the subject site throughout the service life of the proposed
residence, in our opinion, is low; however, the owner should be made aware of the potential for
sinkhole development. If further investigation of possible cavities in the bedrock below the site
is desired, we should be contacted.
FIELD EXPLORATION
The field exploration for the project was conducted on March 4,2020. Three 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 fuck-
mounted CME-458 drill rig. The borings were logged by a representative of Kumar &
Associates,Inc.
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
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inches. This test is similar to the standard penetation ûest described by ASTM Method D-1586
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 peneration resistance values me
shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our
laboratory for review by the project engineer and testing,
SUBSURI'ACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about Yz foat of topsoil overþing loose to medium dense, silty sand down to
depths between 2 and 3 feet. The sand was underlain by dense, slightþ silty gravel down to the
maximum drilled depth of I feet. Drilling in the dense granular soils with auger equipment was
difficult due to the cobbles and possible boulders and drilling refusal was encounæred in the
deposit.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and gradation analyses. Results of swell-consolidation testing performed on relatively
undisturbed drive samples, presented on Figure 4, indicate low to moderate compressibility
under conditions of loading and wetting. Results of gradation analyses performed on small
diameter drive samples (minus IVz-inch fraction) of the coarse granular subsoils are shown on
Figure 5. The laboratory testing is summarized in Table l.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to moist.
FOUNDATION BEARING COIYDITIONS
The shallow sand subsoils encountered at the subject site are low density and possess low
bearing capacity. Spread footings placed on these soils could be susceptible to settlement
particularly if the soils become wetted. The underþing gravel subsoils possess moderate bearing
capacity and a low settlement potential. Spread footings placed on these soils should be suitable
for support of the proposed construction.
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DESIGN RECOMMENDATIONS
FOIINDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the nahral gravel soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural gravel soils should be designed for an
allowable bearing of 3,000 psf. Based on experience, we expect
settlement of footings designed and
be about I inch or less.
2) The footings should have a minimum width of 16 inches fol continuous walls and
2 feet for isolated
3) Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
of foundations at leas:36 :IÞ-Lelow exterior grade is typically used in this
aÍea.
4) Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 10 feet.
Foundation walls acting as retaining structures should also be designed to resist a
lateral earth pressure corresponding to an equivalent fluid unit weight of at least
45 pcf.
5) All existing sand, topsoil and any loose or disturbed soils should be removed and
the footing bearing level extended down to the relatively dense, natural granulæ
soils. The exposed soils in footing area should then be moistened and compacted.
If water seepage is encountered, the footing areas should be dewatered before
concrete placement.
6) A representative ofthe geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
as discussed in this section will
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FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightþ 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 unresfrained
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 (if any) 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 2o/o passing the No. 200 sieve.
All 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 granular soils devoid ofvegetation, topsoil and oversized rock.
LTNDERDRAIN SYSTEM
It is our understanding that the proposed construction will consist of a shallow crawlspace (less
than 3 feet) for the residence and slab-on-grade for the barn. For shallow construction an
underdrain system should not be required. Below are recommendations for an underdrain system
for deeper crawlspace and basement areas (if any).
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
seasonal runoff. Frozen ground during spring runoffcan creat€ a perched condition. ÌVe
recommend below-grade construction, such as retaining walls, deeper crawlspace and basement
areas, be protected from wetting and hydrostatic pressure buildup by an underdrain qystem.
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 lo/oto
a suitable gravrty 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 should be at least IVzfeetdeep.
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SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence and barn have been completed:
1) lnundation 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% of 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 surrounding the exterior of the building should be sloped to
drain away f¡om the foundation in all directions. We recommend a minimum
slope of 6 inches in the first l0 feet in unpaved areas and a minimum slope of
2Yzinches in the first l0 feet in paved areas. Free-draining wall backfill (if any)
should be 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
backfi1l.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this area at this time. We make no warranty either express or implied.
The conclusions and recommendations submitted in this report are based upon the datå obtained
from the exploratory borings drilled at the locations indicated on Figure 1, the proposed type of
constmction and our experience in the area. Our services do not include deærmining the
presence, prevention or possibility of mold or other biological contaminants (MOBC) developing
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 interpolation and extrapolation of the
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.
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This report has besr prepared for the exclusive use by our client for design purposes. We ane not
responsible for technical interpreûations by others of or¡r inforrration. As the project evolves, 1ve
should provide continued consultation and field services during constn¡ction to review and
monitor the impleinentation of or¡r recommendations, and to verify that the rccommendations
have been rypropriately interpreted. Significant design changes may require additional analysis
or modiñcations to the recourmeirdations presented herein. We recommend on-site observation
of excavations and foundation bearing süata and testing of stn¡ch¡ral fill by a representative of
the geotechnical engineer.
Respectñrlly Submitted,
Kumar & Associates, Inc.
P*þ4
James H. Parsons, E.l.
Reviewdby:
E.
JHP/kac
Kumar & Associates, lnc. ri Project No. 20-7-147
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APPROXIMATE SCALE-FEET
20-7-147 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. I
BORING I
EL. 5992.5'
BORING 2EL 5995'
BORING 3
EL. 5996'
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66/12
50/5
WC=8-5 21/12t-
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WC=1.9
+4=65
-2OO=6
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WC=S.9
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-2OO=9
Fig. 2LOGS OF EXPLORATORY BOR¡NGS2A-7-147 Kumar & Associates
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^.r.^ DRIVE SAMPLE BLOW COUNT. IND¡CATES THAT 66 ELOWS OF A I4O-POUND HAMMERool '' FALLTNG so rNcHEs tvERE REQU|RED To DRtvE THE SAMPLER 12 lNcHEs.
.-+ DEPTH AT W}IICI{ BORING CAVED.
f rnlcncll AucER REFusAL
NOTES
1. THE EXPLORATORY BORINGS 1¡gpg þf,tr I ED ON I¡IARCH 1, 2O2O IYITH A 4-INCH-DIAMETER
CONTINUOUS.FUGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS YÚERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON TI{E SITE PI.AN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER
TO TI{E SURVEYED BUILDING CORNER ELEVATIONS.
4. TI{E EXPLORATORY BORING LOCAT¡ONS AND ELEI/ATIONS SI{OULD BE CONSIDERED ACCURATE
ONLY IO THE DEGREE IMPLIED BY THE MET¡{OD USED.
5. TI{E L]NES BETWEEN MATERIALS SI{OWN ON THE EXPLORATORY BORING LOGS REPRESENT TI{E
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE T¡ME OF DRILLING.
7, I¡BORATORY TEST RESULTS:
WC = IYATER CONIENT (X) (ASTM Dl2216);
DD = DRY DENSITY (pcf) (ASTM ù2216)i+1 = PERCENTAGE RETAINEÐ ON NO. ¡[ SIEVE (ASTM D6913);
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTI¡ Dll¡TO).
TOPSOII- SILT, SANDY, ORGANIC, FIRM, IIOIST, DÂRK BROWN.
SAND (S¡¡|-UL): SILIY TO VERY SILTY, LOOSE/SIIFF, llOlST, BROWN.
SAND (SM): SILTY, LOOSE, llOlST, BROWN.
GRAVEL (cP-cM): SANDY, SUGHTLY SILIY ÌVITH COBBTES AND POSSIBLE BOULDERS, DENSE,
MOIST-VERY MOIST, IIIXED BROIYN.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA UNER SAMPLE
DRIVE SAMPLE, I 5,/8-¡NCH I.D. SPUT SPOON STANDARD PENETRATION TEST
LEGEND AND NOTES Fig. 32A-7-147 Kumar & Associates
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SAMPLE OF: Silfy Sond
FRÕM:Borlng2ô2.5'
WC = 8.5 f, DD = 93 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE ÏO WETTING
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20-7-147 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
t(frtmrimmïisü-*:=TABLE 1SUMMARY OF LABORATORYTEST RESULTS20-SOIL fYPESlightly Silty Sandy füavelSilty SandSlightly Siþ Sandy GravelfosfìUNCONFINEDCOMPRESSIVESTRENGTHPLASTICINDEXMIlq.tLIQUID LIMITÄTTERBERG LIMITS69PERCENTPASSING NO.200 stE\E(%)SAND292665GRADATION(9")GRAVEL65NATURALDRYDENSITYlôclì93l%ìNATURALMOISTURECONTENT1.98,53.9fflìDEPTH52V,2Y, &.5SAMPLE LOCATIONBORINGI2J