HomeMy WebLinkAboutSubsoil StudylGrti,ffiåffiiffiiny;-'"
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An Êmffir Oryn¡d Compony
5020 County Road 154
Clenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com
Offrce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Color¿do
RECEIVED
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SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
39 ROYAL COACHMANIS}4 GOLDEN STONE DRIVE
LOT 27, ROARTNG FORK MESA
AT ASPEN GLEN
GARFIELD COUNTY, COLORADO
PROJECT NO.20-7-770
JANUÄRY 21,2021
PREPARED FOR:
CRA}VFORD DESIGN BUILD
ATTN: SIMON BENTLEY
P.O. BOX 1236
CARBONDALE, COLORADO 81623
cdbsimon@comcast.net
TABLE OF CONTENTS
PI.TRPOSF, AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS.............
SUBSIDENCE POTENTIAL
FIELD EXPLORATION ..............
SUBSURFACE CONDITIONS
DESIGN RECOMMENDATIONS
FOUNDATIONS
FOLINDATION AND RETAINING WALLS
FLOOR SLABS..
L'NDERDRAIN SYSTEM
SURFACE DRAINAGE
LIMITATIONS.......
FIGURE I - LOCATION OF EXPLORATORY BORINGS
FIGURE 2. LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS
FIGURE 5 - GRADATION TEST RESULTS
TABLE I- SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Assoc¡ates, lnc. @ Proiect No. 20-7.770
PURPOSE AND SCOPE OF STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on
Lot27, Roaring Fork Mesa at Aspen Glen, Garfield Counfy, 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 agreement for geotechnical engineering
services to Crawford Design Build, dated December 21,2020.
A field exploration program consisting ofexploratory borings was conducted to obtain
infomation on the subsurface conditions. Samples of the subsoils obtained during the field
exploration were tested in the laboratory to determine their classifrcation, compressibility 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. Tl-ris 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 over a crawlspace or basement
level with an attached garage. Ground floor of the garage and basement (if constructed) will be
slab-on-grade. Grading for the structure is assumed to be relatively minor with cut depths
between about 3 to l0 feet. Vy'e assume relatively light foundation loadings, typical of the
proposed type of construction.
If building loadings, location or grading plans change signifrcantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The site was vacant at the time of onr field work. There rnay be frll on this site from previous
overlot grading during subdivision development. Vegetation on the site consisted of grass and
weeds. The lot is relatively flat.
Kumar & Associates, lnc. @ Project No. 20-7-770
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SI I IISIDENCE POTENTIAL
Bedrock of the Penllsylvanian age Eaglc 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 underlie portions of the lot. Dissolution of the gypsum under cefiain
conditions can cause sinkholes to develop and can produce areas oflocalized subsidence.
During previous work in thc arca, scveral sinkholes were obselved scatterecl throughout the
Aspen Glen Development, mainly east of the Roaring Fork River. These sinkholes appear
similar to others associated with the Eagle Vallcy Evaporite in areas of the lower Roaring Fork
River 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
shallorv, for lbundation 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 Lot 27 throughout the service life of the proposed residence, in our
opinion, is low; however, the owner shoulcl 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 January 8,202L Two 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, Inc.
Samples of the subsoils were taken with l% 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
inches. This test is similar to the standard peretration test described by ASTM Method D- 1586.
Thc pcnetration resistance values are an indication of the relative density or consistcncy of thc
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 retumed to our
laboratory for review by the project engineer and testing.
Kumar & Associates, lnc. @ Project No, 20-7.770
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SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
strbsoils consist of about Yz fool of topsoil overlying 16 to 22 feet of medium dense, silty sand
with layers of silty sandy gravel. Below about 15 feet the sands were slightly clayey and less
dense and there are layers ofsandy silt. Relatively dense, silty sand and gravel was encountered
at depths of I 6 to 22 feef and extended down to the depth drilled, 26 feef.
Laboratory testing perfonned on samples obtained from the borings included natural moisture
content and density and gradation analyses. Results of swell-cot-tsolidation testing perfotmed on
a reiatively undisturbed drive sample of tl-re clayey silty sand, presented on Figure 4, indicate low
to moderate compressibility under conditions of loading and wetting and a minor collapse
potential when wetted uncler a constant light load. Results of gradation analyses performed on a
small diameter drive sample of the deeper silty sand and gravel (minus l%-inch fraction) of the
coarse granular subsoils are shown on Figure 5. The laboratory testing is summarizecl in Table 1.
No fi'ee water was encountered irr the borings at the time of drilling and the subsoils were
slightly moist to moist with depth.
DESIGN RECOMMENDATIONS
FOLINDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the naturc of
the proposed construction, we recommend the building be founded with spread footings bearing
on the natural granular soils with a risk of settlement. The settlement potentìal is mainly from
wetting and precautions should be taken to keep the bearir-rg soils chy.
The design and construction criteria presented below should be observed for a spread footing
t-oundation system.
1) Footings placed on the undisturbed natural silty sand soils should be designed for
an allowable bearing pressure of 2,000 psf. Based on experience, we expect
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less.
2) The footìngs should have a minimun width of 1B inches for continuous walls and
2 feet for isolated pads.
Kumar & Associates, lnc. o Project No.20-7-770
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4)
Exteliut luulirrgs and footittgs beneath unheated areas should be provided with
adequal.e soil cover above their bearirig elevation fbr f'rost protection. Placement
oifoundations at least 36 inches below exterior grade is typically uscd in this
area.
continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupporled lerigth of at least l2 feet.
Foundation walls acting as retaining structures should also be designed to resist
lateral earth pressures as cliscussed in the "Foundation and Retaining walls"
section of this repoft.
All existing fiIl, topsoil and any loose or disturbed soils shoulel be removed and
the footing bearir-rg level extended down to the relatively dense natural granular
soils. The exposed soils in footing area should thcn be moistened and compacted.
A representative ofthe geotechnical engineer shoulcl observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
s)
FOLTNDATION AND RETAINING WAT,T,S
Foundation walls and retaining structures which are laterally supported and can be expected to
undergo only a slight amount of deflection should be designed for a lateral eafth pressure
cornputed on the basis of an equivalent fluid unit weight of at lcast 50 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 tull active eafth pressure condition should
be designed for a lateml earth pressurc computed on the basis of an equivalent fluid unit weight
of at least 40 pcf for backfill consisting of the on-site soils.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, constructior-r materials and equipment. The
pressures recommended above assume drained conditions behind the walls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
iucrease the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be providecl to prevent hydrostatic pressurc builclup behind walls.
Backfill should be placecl in utriform lifts and compacted to at least 90% of the ma,rimum
stanclard Proctor density at a moisturc content near optimum. Backfill placed in pavement and
walkway areas should be compacted to at least 95% of the maximum stanclarcl Proctor density.
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6)
Kumar & Associates, lnc. o Project No. 20-7-770
5
Care sl,ould be taken not to overcompact the backfill or use large equipment near the wall, since
this could cause excessive lateral pressnre on the wall. Some settlement of deep foundation wall
backfill should be expected, even if the material is placed correctly, and could result in distress to
facilities constructed on the backfill. Backfill should not contain organics, debris or rock 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 slicling at the bottoms of the footings can be calculated
based on a coefficient of frictioli 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 fì'iction and passive pressure values recomrnended above assume ultimate soil
strength. Suitable factors of safety should be included in the design to limit the strain which will
occur at the ultimate strength, particularly in the case of passive resistance. Fìll placecl against
the sides of the footings to resist lateral loads should be compacted to at least 95% of the
maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of any fill or topsoil. are suitable to support lightly loaded
slab-on-grade construction. To reduce the effects of some differential movement, floor slabs
shoulcl 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 clesigner based on experience and the intended slab use. A minimum 4 inch
layer of free-draining gravel should be 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 2o/o passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least"95o/o of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site granular soils devoid of vegetation, topsoil ancl ovelsized rock.
LINDERDRAIN 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
Kumar & Associates, lnc. o Project No. 20-7-770
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seasulral Iunu.lf. Froeen grountl during spririg runotT'can cl'eate a perched condition. We
recommend below-grade construction, such as retaining walls, crawlspace and basement areas,
be protected from wetting and hydrostatic pressure buildup by an unclerdrain systcm.
The drains should consist of drainpipe 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 of
excavation and at least 1 foot below lowest adjacent fìnish grade and sloped at a minimum l%;o fo
a suitable gravity outlet or drywell. Free-draining granular material used in the undcrdrain
system shoulcl contain less than 2olo passing the No. 200 sieve, less than 50% passing the No. 4
sieve ancl lrave a maximum size of 2 inches. The drain gravel backfill should be at least lYzfeet
deep.
SURFACE DRAINACE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been cornpleted:
l) 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 95Yo of the maximum standard Proctor density in pavement and slab areas
and to at least 90% of thc maximum standard Proctor density in laurJscape areas.
3) The ground surface suruounding the exterior ofthe building should be sloped to
drain away fiom the foundation in all directions. We recommend a minimum
slope of 6 inches in the frrst 10 feet in unpaved areas and a minimum slope of
2Y, inches in the first 10 feet ìn paved areas. Free-draining wall backfill should be
covercd with I'ilter fàbric and capped with about 2 feet of the on-site f,rner graded
soils to reduce surface water infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation shor.lld be located at least
5 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 irigation.
LIMTTATIONS
This study has been condr¡cted in accordance with generally accepted geotechnical engineering
principles and practices in this area aT this time. We make no warranty either express or implied
Kumar & Associates, lnc. @ Project No. 20-7-770
7
The conclusions and recommendations submitted in this report are based upon the data obtained
from the exploratoryborings drilled excavated at the locations indicated on Figure 1, the
proposed type of construction and our experience in the area. Our services do not include
determining the presørce, 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.
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 field 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
ofexcavations and foundation bearing strata and testing ofstructural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
Kumar & Âssoeiates,lnc.
Daniel E. Hardin,
Reviewed by:
*--/.
Steven L. Pawlak, P.E.
DEH/kac
Kumar & Associates, lnc. a Project No. 2ç"7-770
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20-7-770 Kunrar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
BORING 1 BORING 2
0 0
38/ 12
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WC=4.1
-200=46
LL=18
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WC=7.8
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20 20
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+4=41
-200= I 9
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30 30
20-7 -770 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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LEGEND
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1q712 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 15 BLOWS OF A 14O-POUND HAMMER.-/.. FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES,
NOTES
ÏHE EXPLORATORY BORINCS WERE DRILLED ON JANUARY 8, 2A21 WITH A 4-INCH-DIAMETER
CONTINUOUS-FLIGHT POWER AUGER,
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIÐED.
3 ÏHE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY BORÍNGS ARE PLOTTED TO DEPTH,
4. THE EXPLORATORY BORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE
DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRAD.UAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2?16);DD = DRY DENSITY (PCf) (ASTM D2216);+4 = PERCENTAGE RETA.INED ON NO. 4 SIEVE (ASTM 06913);_2OO= PERCENTAGE PASSING NO. 2OO SIËVË (ASTM D1140);LL = LIQUID LIMIT (ASTM D4318);Pl = PLASTICITY INDEX (ASTM D43tB).
IOPSOILi ORGANIC SANDY SILTY CLAY WITH GRAVEL, FIRM, MO|ST, DÀRK BROWN.
SAND (SM); SILTY TO VERY SILTY, CLAYEY AT DEPTH, SCÀTTERED GRAVEL, MEDIUM DENSE,
SLIGHTLY MOIST, REDDISH BROWN.
SAND AND GRAVEL (SM_GM); SILTY, DENSE, SLIGHTLY MOIST, BROWN TO REDDISH BROWN,
GRAVEL (GM); S¡IIOY, SILTY WITH COBBLES, VERY DENSE, MoIsT, BRowN.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE, 1 5/8-tNCH LD. SPLIT SPOON ST,ANDARD pENETRAT|0N TEST.
2A-7 -770 Kunrar & Associates LEGEND AND NOTES Fis. 5
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SAMPLE OF: Cloyey Silty Sond
FROM:Boring2@15'
WC = 7.8 %, DD = 98 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANÎ PRESSURE
DUE TO WETTING
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20-7-770 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
SIEVE ANALYSIS
1
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C6R SQUARE OPÊNINCS
HYDROMEIER ANALYSIS
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90
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60
50
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50
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OF INM
CLAY TO SILT COBBLES
GRAVEL 41 % SANO
LIQUID LIMIT
SAMPLE OF: Sllty Sond qnd crov€l
40
PLASIICIfY INDEX
SILI ANO CLAY 19 %
FROM:Boringt O20'
fhagg lall rosults opply on[y lo lh€
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occordoncB w¡th ASTM 06915, ASTM D7924,
ASTM C136 ondlor ASTM Dll,l0.
SAND GRAVEL
FINE MEDTUM lcO^RSF FINE COARSE
20-7-770 Kumar & Associates GRADATION TEST RESULTS Fig. 5
l*rt¡.ffi,ffifffi1rå;å**TABLE ISUMMARY OF LABORATORY TEST RESULTSNo.20-7-770SOIL TYPEUNCONFINEOCOMPRE$SIVESTRENGTHVery Silty SandSilty SandSlightly Clayey Sandy SiltSilty Sand and GravelSilty Sand with GravelSilty Sand and GravelClayey Silty Sandlo/"1PTASTICINDÐ(2ATTERBERG LIMITSL¡QUID LIMITP/"1I1PERCE¡TTPASSING NO,200 srEVE46337691t3zof/"',SAND4041GRADATIONl"/rlGRAVELlocflNATURALDRYDENSITY116l0s110133984.14.613.6132.61.97.8loklNATURALMOISTURECONTENT{ft)DEPTH501l52A5101512SAMPLE LOCATIONBORING