HomeMy WebLinkAboutSubsoil Study for Foundation Design 01.23.19l(+rt
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lf¡mar & As¡octrþs, lnc,
Ceotechn¡cal ând Materials Engineers
and Environmental Scienlsts
kumarug¡.com
5020 County Road'154
Glenwood Springs, CCI 816CI1
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www.kumarusa.comMf]MBER
ûffice Locations: Ðenver {HQ), Parker, Colorado Springs, Fort Coilins, Glenwood $prings and Summit County, Colorado
January 23,2019
Conor Corkery
617 Penny Lane
Cedar Park, Texas 78613
tcdb-o¡-da@s¡ailçp.ll
RECEIVED
Project No. 19-7-100
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 15, Filing 6, Elk
Springs, ó47'Wood Nymph Lane, Garfield County, Colorado
Dear Mr. Corkery:
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 proposal for geotechnical
engineering services to you dated August 16, 2018. The data obtained and our recommendations
based on the proposed construction and subsurface conditions encountered are presented in this
report. Hepworth-Pawlak Geotechnical, Inc. (now Kumar & Associates, Inc.), previously
performed a preliminary geotechnical study for Filings ó thru 9, Elk Springs (formerly Los
Amigos Ranch PUD) and presented the findings in a report dated February 14,1997, Job No.
196 617.
Proposed Construction: The proposed residence will be a one-story wood frame structure over
a walkout basement level with an attached E rage located on the site as shown on Figure 1.
Ground floors will be slab-on-grade. Cut depths are expected to range between about 2 to I 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.
Site Conditions: The site is located on a rolling mesa at an elevation of about 7,100 feet. There
was about 2 to 3 feet of snow cover at the time of our field exploration. Vegetation consists of
sage brush, native grass and weeds, and scattered juniper trees. The ground surface slopes down
to the west at a grade of about 10 percent with about 8 feet of elevation difference across the
building fooþrint.
APR 2 6 2019
GARFIELD COUNTY
COMMUNITY DEVELOPMENT
-2-
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
three exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about I foot of topsoil, consist of basalt
gravel, cobbles and boulders in a silty sand matrix. Results of a gradation analysis performed on
a sample of very silty sandy gravel (minus S-inch fraction) obtained from the site are presented
on Figure 3. No free water was observed in the pits at the time of excavation and the soils were
slightly moist to moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, \rye recommend spread footings
placed on the undisturbed natural basalt gravel soil designed for an allowable soil bearing
pressure of 2,000 psf for support of the proposed residence. The matrix soils tend to compress
after wetting and there could be some post-construction foundation settlement. Footings should
be a minimum width of 16 inches for continuous walls and 2 feet for columns. The deeper cut
areas and utility trenches may require rock excavating techniques such as blasting or chipping
due to the basalt boulders. 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. Voids created from boulder removal should be filled with a structural
material such as road base and compacted to at least 95% standard Proctor density at a moisture
content near optimum. We should observe the completed excavation for bearing soils prior to
placing backfill material or concrete. 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 and bottom to span local anomalies such as by assuming an unsupported length of
at least l0 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 excluding rock larger than 6 inches. Resistance to sliding at the bottoms of the
footings can be calculated based on a coefücient of friction of 0.45. Passive pressure of
compacted backfill against the sides of the footings can be calculated using an equivalent fluid
unit weight of 400 pcf. The coefficient of friction and passive pressure values recommended
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, particulady in the case of passive
resistance.
Kumar & Associates, lnc.Project No, 19-7-100
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Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly 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 reduce damage due
to shrinkage oracking. The requireurents 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 to facilitate drainage.
This material should consist of minus 2-inch aggregate with less than 50o/o passing the No. 4
sieve and less than 20/øpassingthe 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 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 area that local perched groundwater can develop during times of
heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create 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 underdrain
system.
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 1 foot below lowest adjacent finish grade and sloped at a minimum l%ó to
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 lYz feet deep.
Surface Drainage: 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 shoultl be adjusted to near optimum moisture and compacted to
at least 95Yo of themaximum standard Proctor density in pavement and slab areas
Kumar & Associates, lnc.Project No, 19-7-100
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4)
and to at least 90% of the maximum standard Proctor density in landscape areas.
Free-draining wall backfill should be covered with filter fabric and capped with
about2 feet of the on-site, finer graded soils to reduce surface water infiltration.
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 6 inches in the first 10 feet in unpaved meas and a minimum slope of
3 inches in the first 10 feet in pavement and walkway areas. A swale will be
needed uphill to direct surface runoffaround the residence.
Roof downspouts and drains should dischmge well beyond the limits of all
backfill.
Landscaping which rèquires regular heavy irrigation should be located at least
5 feet from the building.
s)
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 data obtained from the exploratory pits excavated at the locations indicated on Figure 1
and to the depths shown on Figure 2,theproposed t¡pe 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 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 pits 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 at once so 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 veriry 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
3)
Kumar & Associates, lnc.Project No. 19-7-100
5
of excavations and foundation bearing süata and testing of structural fill by a representative of
the geotechnical engineer.
If you have any questions or if we may be of firther assistance, please let us know.
Respec'tfirlly Submitted,
K¿¿c&*r *& ",L*ss¡cår*tes" lr¡€.
W,//^Ål p*-
Robert L. Duran, E. l.
Reviewed by:
Steven L. Pawlak, P
RLD/kac
attachments PitsFigure 1-
Figure 2 -I¡gs Pits
Figure 3 * Gradation Test Results
Table I - Summary of Laboratory Test Results
DM Neuman - Rich Carter (rteh(r0d4neunan'çoq)
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Kumar & Associates, lnc.Project No. f9-7-10CI
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Figure 1LOCATION OF EXPLORATORY PITS19-7-100 Kumar & Associates, lnc,
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LEGEND
TOPSOIL, CLAY AND SILT, SANDY, FIRM, SIIGHTLY MOIST, BROWN, SLIGHTLY ORGANIC.
BASALT GRAVEL, COBBLES, AND BOULDERS IN A SILTY SAND TO SANDY SILT MAÏRIX
(GC-ML), MEDTUM DENSE TO DENSE, SLIGHTLY MOIST, LIGHT TAN. CALCAREOUS.
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DISTURBED BULK SAMPLE.
î PRACTICAL DIGGING REFUSAL.
NOTES
1. TI{E EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JANUARY 18,20f9.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULO BE CONSIDTRED ACCURATE ONLY
TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAT TYPES AND THE ÏRANSITIONS MAY BE
GRADUAL.
6. GROUND WATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF DIGGING. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM Ð 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
-2OO= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140);
LL = LIQUID LIMIT (ASTM D 4518);
Pl = PLASTICITY INDEX (ASTM D 4318).
I 9-7- 1 00 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
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1 9-7- 1 00 Kumar & Associates GRADATION TTST RESULTS Fig. 5
l(+rtl(tn&lsrocffi,lnc.Geotechnicâl and Materiåls EngirÊersand Envlronmental Scientistskumarusa.comTABLE ISUMMARY OF LABORATORY TEST RESULTSPro¡ec{ No. l9.7.llþSOILTYPEVery Silty Sandy Gravelwith CobblesulcolrFlltEocorPREss,rì,ESTREIIGTH(o¡fll"ffifsPl¡STrcilDexf%ìI3AÎERBLK¡UDUilTt%t40PERCEI¡TPASS|IiG ilO.200 stB,E39GRADATþIIsff{Df¡)25GRAIÆL(%)36¡IAÎURALDRYDEilSftYlDGfì]IATURALflorsfuREcolTEl{TFlolt4.3SAIIPLELOCATIONDEPTHffrì2-3Pfr2