HomeMy WebLinkAboutSubsoil StudyI (aJf iiffii[ffif¡$i*'"'Ë;' **'
An Employcc Onrncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com
Office t¡cations: Dørver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
TBD CÄ.TTLE DRIVE
TRACT 43
ANTLERS ORCHARD DEYELOPMENT
GARFIELD COUNTY, COLORADO
PROJECT NO.22-7-122
FEBRUARY 24,2022
PREPARE,D FOR:
JESSE F'LOWERS
LTI?BALLARD AVENUE
SILT, COLORADO 81652
(eambit2248@Yahoo )
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS.......
FIELD EXPLORATION
SUB SURFACE CONDITIONS .
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS
FOUNDATIONS
FLOOR SLABS
I.INDERDRAIN SYSTEM ........
SITE GRADING.
SURFACE DRAINAGE
LIMITATIONS
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS
TABLE 1 - STJMMARY OF LABORATORY TEST RESULTS
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Kumar & Associates, lnc. @ Project No.22-7-122
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located at TBD
Cattle Drive, Truct 43, Antlers Orchard Development, Garfield County, Colorado. The project
site is shown on Figure 1. The pu{pose 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 Jesse Flowers dated January 14,2422.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils and bedrock 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 one to two-story, wood-framed structure over a crawlspace
with a slab-on-grade garage floor. Grading for the structure is assumed to be relatively minor
with cut and fill depths between about 3 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 recoÍtmendations contained in this report.
SITE CONDITIONS
The site was vacant and had a few inches of snow cover at the time of our site visit. The
proposed building footprint is located on a relatively natural hillside with a graded access trail.
The ground surface is covered with scattered grasses, weeds, sage brush and juniper trees and, in
general, moderately to steeply sloping down to the west, south and southeast. Steeper slopes are
present further uphill to the north. Inside the building footprint area, the slope is moderately to
strongly sloping down to the southwest.
Kumar & Associates, lnc. o Project No.22-7-122
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FIELD EXPLORATION
The field exploration for the project was conducted on January 25,2022. Two exploratory
borings were drilled at the locations shown on Figure 1 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 and bedrock were taken with l%-inch and 2-inchl.D. spoon samplers.
The samplers were driven into the subsurface materials 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-1586. The penetration resistance values are an indication of the relative
density or consistency of the subsoils and hardness of the bedrock. 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.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils, below about I foot of organic sandy, silty clay, consisted of about lYzto 2 feet of firm
sandy siþ clay and medium dense clayey sand with gravel. The subsoils were underlain at
depths of 2%and 3 feet by medium hard to very hard siltstone and claystone bedrock.
Laboratory testing performed on samples obtained from the borings included natural moisture
content, Atterberg limits, and swell-consolidation. Results of swell-consolidation testing
performed on a relatively undisturbed drive sample, presented on Figure 4, indicate no expansion
and relatively low compressibility under conditions of loading and wetting. The laboratory
testing is summarizedinTable 1.
No free water was encountered in the borings at the time of drilling and the subsoils and bedrock
were slightly moist to moist.
F'OUNDATION BEARING CONDITIONS
The upper sand and clay soils possess a low bearing capacity and a low settlement or expansion
potential if wetted. Testing indicates the underþing claystone/siltstone bedrock is non-expansive
and has low compressibility potential. Shallow spread footings placed entirely on the bedrock
can be used for support of the proposed residence with a low risk of foundation movement' We
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should observe the subsurface conditions exposed at the time of excavation and evaluate them
for swell-compression potential and possible mitigation. Proper surface drainage as described in
this report will be critical to the long-term satisfactory performance of the structure.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded on spread footings bearing on
the natural bedrock.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural bedrock should be designed for an
allowable bearing pressure of 3000 psf. Based on experience, we expect
settlement or heave of footings designed and constructed as discussed in this
section will be about 1 inch or less.
2) The footings should have a minimum width of 16 inches for continuous walls and
24 inches 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
atea.
4) Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 12 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
55 pcf for the onsite soils as backfill.
5) The topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the relatively hard bedrock. The exposed soils in
footing area should then be moistened and compacted. We should evaluate the
exposed bedrock for expansion potential and the need for subexcavation and
placement of structural frllfor movement mitigation.
6) A representative ofthe geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
Kumar & A¡sociates, lnc. o Project No.22-7-122
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FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade
construction with a risk of movement. To reduce the effects of some differential movement,
floor slabs should be separated from all bearing walls and columns with expansionjoints 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 free-draining gravel should be placed beneath 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?Yo passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95Vo of maximum
standard Proctor densþ at a moisture content near optimum. Required fill can consist of the on-
site granular soils devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
Atthough free water was not encountered during our exploration, it has been our experience in
the area and where bedrock is shallow 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 I foot below lowest adjacent finish grade and sloped at a minimum IYo 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 50olo passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least lYzfeet deep.
SITE GRADING
The risk of construction-induced slope instability at the site appears low provided the building is
located in the less steep slope area as planned and cut and fill depths are limited. 'We assume the
cut depths for the crawlspace level will not exceed about 3 to 5 feet. Difficult excavation in the
bedrock should be anticipated. Fills should be limited to about I feet deep. Embankment fills
should be compacted to at leastg5Yo of the maximum standard Proctor density near optimum
Kumar & Aseociates, lnc. @ Project No.22-7-122
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moisture content. Prior to fill placement, the subgrade should be carefully prepared by removing
all vegetation and topsoil and compacting to at least 95Yo of the maximum standard Proctor
density. The fill should be benched into the portions of the hillside exceeding 20Yo grade.
Permanent unretained cut and fill slopes should be graded at2horizontal to I vertical (2H:lV) or
flatter and protected against erosion by revegetation or other means.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
1) Inundation of the foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfrll 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 90Vo 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 10 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in paved areas. Free-draining wall backfill should be
covered with frlter fabric and 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
backfill.
5) Landscaping which requires regular heavy irrigation should 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 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.
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 1, the proposed type 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
Kumar & Associales, lnc. o Project No.22-7-122
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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 veriry that the recommendations
have been appropriatelyinterpreted. 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.
Respectfirlly Submitted,
Kumar & Associates, Inc.
%/fu
Mark Gayeski, E.I.T.
Reviewed by:
Steven L. Pawlak,
SLP/kac
Cc: J. Caliber ( i ose(grj caliberconstruction. com)
Kumar & Associates, lnc. o Project No.22-7-122
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22-7-122 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
BORING 1 BORING 2
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3s/6,50/4
WC=5.6
DD= 1 28
LL=25
Pl=10
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Fig. 2LOGS OF EXPLORATORY BORINGSKumar & Associates22-7-122è
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LEGEND
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TOPSOIL: ORGANIC SANDY SILTY CLAY, FIRM, SLIGHTLY MOIST, LIGHT BROWN TO TAN
SAND (SC): CLAYEY W|TH GRAVEL, MEDIUM DENSE, SLIGHTLY MOIST, TAN, ROOTS.
CLAY (CL): SANDY, SILTY, FIRM, SLIGHTLY MOIST, GRAYISH-TAN
Át/CLAYSTONE AND SILTSTONE BEDROCK: INTERLAYERED, SLIGHTLY SANDY WITH OCCASIONAL
SHALLOW THIN SANDSTONE LENSES, MEDIUM HARD TO VERY HARD WITH DEPTH, SLIGHTLY
MOIST TO MOIST, GRAYISH_TAN TO GRAY.
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DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
DRTVE SAMPLE, 1 s/1-lNcH l.D. SPLIT-SPOON STANDARD PENETRATION TEST
87 /12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 87 BLOWS OF A l4O_POUND HAMMER
FALLING 50 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON JANUARY 25, 2O2Z WITH A 4-INCH DIAMETER
CONTINUOUS_FLIGHT POWER AU6ER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY BORINGS 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 GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
V"C = WATER CONTENT (%) (ASTM D2216);
DD = DRY DENSITY (PCf) (ASTM D2216);
LL = LIQUID LIMIT (ASTM DA518);
Pl = PLASTICITY INDEX (ASTM D4518).
22-7-122 Kumar & Associates LEGEND AND NOTES Fig. 5
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SAMPLE OF: Cloystone/Siltstone
FROM: Boring 2 @ 10'
WC = 9.1 26, DD = lf I pcf
NO MOVEMENT UPON
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FTg. 4SWELL_CONSOLIDATION TTST RESULTSKumar & Associates22-7-122
lGrt[ffii[ffi:ffi*iiiå**TABLE 1SUMMARY OF LABORATORY TEST RESULTSClaystone/SiltstoneSOILTYPEClaystone/SiltstoneClaystone(psflUNCONFINEDCOMPRESSIVESTRENGTHt9(o/olPLASTICINDEX1025{%)LIQUID LIMIT36ATTERBERG LIMITSPERCENTPASSING I{0.200 stEvEiloNSANDli/"\(%)GRAVEL128118NATURALDRYDENSITYlocf)I9lololNATURALMOISTURECONTENT3.67.5501{ft}DEPTH2v,12SAMPI.E LOCATIONBORINGNo.22-7-122