HomeMy WebLinkAboutSubsoil Studylcrt Ítmar & âsroGlates,lnc,
Geotechnical and Materials Engineers 5020 County Road 154
and Environmental Scientisb Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employcc oìrncd Compony www.kumarusa.com
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SUBSOIL STUDY
F'OR F'OI]IIDATION DESIGN
PROPOSED RESIDENCE
LOT 5, MrI\IEOTA RIDGE ESTATES, FTLTNG 3
MTNEOTA DRIVE, SOUTH OF SILT
GARFTELD COUNTY, COLORADO
PROJECT NO. 20-7-385
AUGUST 10,2020
PREPARED FOR:
IGOR AND ELENA SKAKOVSKY
5165 COUNTY ROAD 331
srLT, coLoRADO 81652
sisorco(øhotmail.com
TABLE OF CONTENTS
PIJRPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION ..
SITE CONDITIONS
FIELD ÐGLORATION ..........
SI JB SURFACE CONDITIONS
FOTJNDATION BEARING CONDITIONS .........
1
1-
2-
2-
1
-3-
DESIGN RECOMMENDATIONS
FOUNDATIONS.....
NON.STRUCTIJRAL FLOOR SLABS...... ,...,..,..4 .
UNDERDRAIN SYSTEM ..................4.
SURFACE DRAINAGE -5-
LIMITATIONS 5-
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4. SWELL.CONSOLIDATION TEST RESIJLTS
TABLE 1- SIJMMARY OF LABORATORY TEST RESULTS
3-
3-
Kumar &Aseoolatee, lnc. ?PrcJrc,t No.20.7.385
PT]RPOSE AT\D SCOPE OF STT]DY
This report presents the results of a subsoil study for a proposed residence to be located on Lot 5,
Mineota Ridge Estates, Filing 3, Mineota Drive, south of Silt, Garfield County, Colorado. The
project site is shown on Figure 1. The prrrpose 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 Igor and Elena Skakovsþ dated June 30,2020.
A field exploration progr¿rm 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 determine 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 foundation. 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 single-story structure with slab-on-grade floor. Grading for the
structure is assumed to be relatively minor with cut depths between about 2 to 3 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 COI\DITIONS
The lot is located along the uphill side of Mineota Drive and was vacant at the time of our field
exploration. The ground surface within the designated building site (between the exploratory
borings shown on Figure l) was relatively flat with around 3 to 4 feet of elevation difference.
Sandstone formation outcrops were observed in the uphill, south part of the lot and within the
Kumar & Associates, lnc. o Project No.20-7-385
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powerline easement shown on Figure 1. Vegetation consisted of grass and weeds with scattered
cacti in the building site and scattered pinon trees in the higher elevation, south part of the lot.
FIELD EXPLORATION
The field exploration for the project was conducted on July 14, 2020. 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 a 2-inch I.D. spoon sampler. The sampler was driven
into the subsoils at various 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-l586. 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 penetration resistance values are
shown on the Logs of Exploratory Borings, Figure 2. The samples were refurned to our
laboratory for review by the project engineer and testing.
SUBSURF'ACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils encountered, below about lzfoot oftopsoil, consist ofaround 2I to23 feet ofvery stiff
to hard, sandy siþ clay with gravel underlain by very stifflmedium dense clay and sand with
gravel. At Boring 2, relatively dense, silty clayey sand and gravel was encountered at 28 feet
down to the boring depth of 32 feet.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and finer than sand size gradation analyses. Results of swell-consolidation
testing performed on relatively undisturbed drive samples of the upper clay soils, presented on
Figure 4, indicate low to moderate compressibility under conditions of loading and wetting. The
samples showed minor collapse or expansion upon wetting under light loading. The laboratory
testing is summarizedinTable l.
Kumar & Associates, lnc. o Project No.20-7-385
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No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
FOT]NDATION BEARING COI\DITIONS
The subsoils encountered in the borings at shallow depth are typically low shength clays with
variable low to moderate compressibility. Shallow spread footings or structural slab with turned
down edges placed on the natural soils should be suitable for the building support with a risk of
differential movement, mainly when the bearing soils are wetted. A heavily reinforced structural
slab will help to mitigate the effects of differential movements and limit building distress.
DESIGN RECOMMEI\DATIONS
FOUNDATIONS
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 or
structural slab bearing on the natural soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils should be designed for an
allowable bearing pressure of 1,500 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 around I inch of additional settlement if
the bearing soils are wetted, depending on the depth and extent of subsurface
wetting. Structural slabs can be designed for a subgrade modulus of 100 tcf.
2) The footings should have a minimum width of 20 inches for continuous walls and
2 feet for isolated pads.
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 least 36 inches below exterior grade is typically used in this
area. Structural slab should have a perimeter turn down edge at least 18 inches
deep and be frost protected with minimum 2-inchthick rigid foam insulation
extending out at least2 feet from the foundation edge.
Kumar &Associates, lnc. o Project llo.20-7-385
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Continuous foundation walls should be heavily reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 14 feet.
Foundation walls acting as retaining structures (if any) should also be designed to
resist a lateral earth pressure corresponding to an equivalent fluid unit weight of at
least 55 pcf for the onsite soils as backfill.
The topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the firm soils. The exposed soils in footing areas
or below structural slab areas should then be moistened and compacted.
Structural fill placed below foundation areas should be compacted to atleast9SYo
of standard Proctor density atnear optimum moisture content.
A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
NON-STRUCTURAL FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade
construction with a risk of settlement if the bearing soils are wetted. To reduce the effects of
some differential movement, non-structural 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 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 relatively well graded sand
and gravel such as road base should be placed beneath slabs for support. This material should
consist of minus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less than
l2%o passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95Vo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site soils devoid of vegetation and topsoil.
UNDERDRAIN SYSTEM
It is our understanding that the proposed finished floor elevation at the lowest level is at or above
the surrounding grade. Therefore, a foundation drain system is not required. It has been our
4)
5)
6)
Kumar &Associates, lnc. o Project No.20-7-385
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experience in the area and where there are clay soils that local perched gloundwater 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
and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain
and wall drain system.
If the finished floor elevation of the proposed structure is revised to have a floor level below the
surrounding grade, we should be contacted to provide recommendations for an underdrain
system. All earth retaining structures should be properly drained.
SURFACE DRAINAGE
Proper surface grading and drainage will be critical to limiting subsurface wetting and potential
building movements. 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 andunderslab areas shouldbe avoided
during construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95o/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.
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 first l0 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in paved areas.
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 foundation walls. Consideration should be given to use of xeriscape
to reduce the potential for wetting of soils below the building caused by irrigation.
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.
Kumar & Associates, lnc. o Project No.20-7-385
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The conclusions and recommendations submitted in this report are based upon the data obtained
from the exploratory borings drilled at the locations indicated on Figure l, the proposed type of
construction and our experienoe in the area. Our services do not ineludedetemining the
presence' prevention or possibility of mold or other biological contaminants (MOBC) developing
in the future. If the client is concemed 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
of excavations and foundation bearing strata and testing of structural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
Kumar & Associates, fnc.
S teven L. Pawlak, P.
Reviewed by:
QJç ?-
Daniel E. Hardin, P.E.
SLPlkac
cc: JeffJohnson
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Kumar & Associates, lnc, ;,
Project No, 20.7.38S
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BORING 1
EL. I 00'
BORING 2
EL. 1 05'
DD= 1 09 ae/ tz
5 23/12
WC=5.6
DD=l12
-200=65
31 /12
WC=6.8
DD=1 1 0
5
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1032/12
- 15 1544/ 12 38/12
WC=6.7
DD=117
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DD=1 15
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-25 2546/6,50/5 41/12
-50 40/6,50/ 4 46/ 12
50
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-40 40
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20-7 -385 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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LEGEND
TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, DARK BROWN
CLAY (CL); SILTY,-SANDY, SCATTERED GRAVEL, VERY -STIFE TO HARD, SLIGHTLY MOISI,
LIGHT BROWN, CALCAREOUS TRACES.
n CLAY AND SAND (CL-SC); SILTY, SCATTERED GRAVEL TO GRAVELLY, VERY STIFF/MEDIUM
DENSE, SLIGHTLY MOIST, BROWN.
SAND AND GRAVEL (SC-GC); CLAYEY, SILTY, MEDIUM DENSE TO DENSE, SLIGHTLY MOIST,
BROWN.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
.R11. DRIVE SAMPLE BLOW COUNT. INDICATES THAT 25 BLOWS OF A 14O-POUND I{AMMER'r/ t' FALL|NG 30 tNcHES WERE REeU|RED To DRtvE THE SAMPLER 12 lNcHEs.
NOTES
THE EXPLORATORY BORINGS WERE DRILLED ON JULY 14,2O2O 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 SIÏE PLAN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER
TO BORING 1 AS EL. = 100', ASSUMED.
4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS 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 GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULÏS:
wc = WATER CoNTENT (%) (ASTM D2216);
DD = DRY DENSITY (pcf) (ASTM D2216);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM Dl140).
20-7 -385 Kumar & Associates LEGEND AND NOTES Fig. 3
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SAMPLE OF: Sondy Silty Cloy
FROM:Boring2@-5'
WC = 6.8 %, DD = 110 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
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1.0 APPLIED PRESSURE - KSF
SAMPLE OF: Sondy Sílty Cloy
FROM:Boringl@2.5'
WC = 6.3 %, DD = 109 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTINGlr'-
\)
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20-7 -385 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig.4
I(+'THffifiMMF*"TABLE ISUMMARY OF LABORATORYTEST RESULTSSandy Siþ ClaySandy Silty ClaySandy Silty ClaySandy Siþ ClaySandy Silty ClaySOIL TYPEf¡sflUNCO}¡FINEDcottPREssll,ESTRENGT1It%lPLASTICINDEXATTERBERG LIIIITSLIQUID LIM]Tl'lolPERCENTPASSING NO.200 s¡Eì,E6378SANDlf/,|GRADATION('l,lGRAVEL109tt2lt5110tt7Î{ATURALDRYDENSITYl¡cfl(ololNATURALMOISTURECONTENT6.35.67.46.86.72y,52055ItftìDEPT}ISAìIPLE LOCATIOilBORING12No.20-7-385