HomeMy WebLinkAboutSubsoil Study for Foundation Design 02.11.2022l(+A#ffii,ffi:iri'"*
r,n anssrycr oqmcd compsry
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Sumrnit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE AI\D BARN
9174 HIGHWAY 82
GARFTELD COUNTY, COLORADO
PROJECT NO.22-7-115
FEBRUARY 11,2022
PREPARED FOR:
BRANDON COWHEY
571 RIVERBEND WAY
GLENWOOD SPRINGS, COLORADO 81601
cow hev bra n don @,q mail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS
SUBSIDENCE POTENTIAL.
FIELD EXPLORATION
SUBSURFACE CONDITIONS
DESIGN RECOMMENDATIONS ........
FOUNDATIONS
FLOOR SLABS
UNDERDRAIN SYSTEM..
SURFACE DRAINAGE......
LIMITATIONS
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 . GRADATION TEST RESULTS
TABLE 1 - SUMMARY OF LABOMTORY TEST RESULTS
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Kumar & Associates, lnc. @ Project No. 22-7-'ll5
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PURPOSE AND SCOPE OF STUDY
T'his report presents the results of a subsoil study for a proposed residence and bam to be located
at9l74 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 agreement for geotechnical engineering services to Brandon
Cowhey, dated January 13,2022.
A flreld 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 determine their classification 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
At the time of our study, design plans for the residence had not been developed. For the
purposes of our analysis, we assume proposed residence will be a wood-framed structure with
attached garugeand a detached barn. Ground floors will be structural floor over crawlspace in
the residence and slabs-on-grade for the garage and barn. Grading for the structure is assumed to
be relatively minor with cut depths between about 4 to 7 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 lot was vacant of structures at the time of our visit. Vegetation consists of grass and weeds,
and the ground surface is relatively flat with a gentle slope down to the southwest. The lot is
situated on a terrace above the Roaring Fork River, which borders the lot on the southwest.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies most of the lower Roaring
Fork Valley, including the subject site. These rocks are a sequence of gypsiferious shale, fine-
Kumar & Associates, lnc. o Project No. 22-7-'115
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grained sandstone/siltstone and limestone with some massive beds of gypsum. There is a
possibilify that massive gypsum deposits associated with the Eagle Valley Evaporite underlie
portions of the property. Dissolution of the gypsum under certain conditions can cause sinkholes
to develop and can produce areas of localized subsidence. During previous work in the area,
several broad subsidence areas and sinkholes have been observed. These sinkholes appear
similar to others associated with the Eagle Valley Evaporite in areas of the lower Roaring Fork
River valley.
No evidence of subsidence or sinkholes were observed on the property or encountered in the
subsurface materials, howevero 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 at the
site throughout the service life of the structure, in our opinion is low, however the owner should
be 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 18,2022. Three 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 and
Associates.
Samples of the subsoils were taken with a l%inchand2inch 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 penetration test 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 penetration resistance values are
shown on the Logs of Exploratory Borings, Figure 2. The samples were returned 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 6 inches of topsoil, consist of about l%to 3% feet of stifl sandy silt
underlain by relatively dense, silty sandy gravel with cobbles and probable small boulders
Kumar & Associates, lnc. o Project No. 22-7-1'15
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(alluvium) down to the maximum depth explored of 8 feet. Drilling in the dense granular soils
vrith auger equipment was difficult due to the cobbles and boulders and drilling refusal was
encountered in all three borings in the deposit.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and gradation analyses. Results of gradation analyses performed on a small diameter
drive sample (minus l%-inch fraction) of the coarse granular subsoils are shown on Figure 3.
The laboratory testing is summarizedin Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the buildings be founded with spread footings bearing
on the natural granular soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
l) Footings placed on the undisturbed natural granular soils below all sandy silt
soils, should be designed for an allowable bearing pressure of 3,000 psf, Based
on experience, we expect settlement of footings designed and constructed as
discussed in this section will be about I inch or less.
2) The footings should have a minimum width of 16 inches for continuous walls and
.2 feefforisolated Pads. -----3) Exterior footings and footings beneath unheated areas should be provided with
dequate 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 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 for the onsite sand and gravel soil as backfill.
Kumar & Associates, lnc. @ Project No. 22-7-115
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All topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the relatively dense natural granular soils. The
exposed soils in footing area should then be moistened and compacted.
6) A representative ofthe geotechnical engineer should observe
excavations prior to concrete placement to evaluate bearing conditions.
FLOOR SLABS
The natural on-site granular soils, exclusive of topsoil, are suitable to support lightly loaded slab-
on-grade construction. The sand and silt soils have settlement potential which could result in
some slab movement if the bearing soils become wetted. To reduce the effects of some
differential movement, floor slabs in the garage and barn areas 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 well graded sand and
gravel (such as road base) should be placed beneath interion slabs-on-grade for subgrade 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. If slab-on-grade construction is used inside
the house, some sub-excavation of the silt soils may be needed to reduce potential settlement.
All fill materials for support of floor slabs should be compacted to at least 95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site granular soils or suitable imported granular fill devoid of vegetation, topsoil and oversized
rock.
UNDERDRAIN SYSTEM
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 constructiono such as retaining walls, crawlspace and
basement areas, be protected from weffing and hydrostatic pressure buildup by an underdrain and
wall drain 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 lYoto
s)
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a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain
system should contain less than 2Topassingthe 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 lYzfeet
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 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 from 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
3 inches in the first 10 feet in paved areas. Free-draining wall backfill should be
covered with filter fabric and capped with about 2 feet of the on-site finer graded
soils to reduce surface water infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this area atthis 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 I, 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
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.
Kumar & Associates, lnc. @ Project No. 22-7-'115
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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 verify 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, .
K$sxlar & .4ss*c*st*s, Xme-
David A. Noteboom, StaffEngineer
Reviewed by:
Daniel E. Hardin,
DEHlkac
Kumar & Atscclateso lne. tr Proiec{ t{a. 32-?-tl$
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Fig. 1Kumar & Associates LOCATION OF EXPLORATORY BORINGS22-7-115
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BORING 1 BORING 2 BORING 5
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WC=6.1
DD=90
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-2OQ=12
50/6 so/5
10 10
LEGEND
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TOPSOIL; SANDY CLAY AND SILT, ORGANICS AND ROOTS, FIRM' MOIST' BROWN
SILT (ML); VERY SANDY, STIFF, SLIGHTLY MolST, BROWN' SLIGHTLY POROUS
W
GRAVEL (GM); SANDY, SILTY, WITH COBBLES AN
VERY DENSE, SLIGHTLY MOIST, BROWN, ROUNDE
DS
DR
MALL BOULDERS, DENSE TO
OCKS.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
I DRTVE SAMPLE, 1 3/8-INCH l.D. SPLIT SPOoN STANDARD PENETRATION TEST.
AI'^ DRIVE SAMPLE BLOW COUNT' INDICATES THAT 13 BLOWS OF A 140-POUND HAMMER
''/ '' FALLTNG 30 tNcHES WERE REeU|RED To DRIVE THE SAMPLER 12 lNcHES.
I nnlcrrcnL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON JANUARY 18, 2021 WITH A 4-INCH-DIAMETER
CONTINUOUS-FLIGHT POWER AUGER.
2. THE EXPLORATORY BORINGS WEBE LOCATED BY THE CLIENT.
3. 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:
wc = WATER CoNTENT (%) (ASTM D2216);
DD = DRY DENSITY (PCT) (ISTV D2216)I
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6915);
_2QO= PERCENTAGE PASSING NO.2OO SIEVE (ASTM Dl140).
22-7 -1 15 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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DIAMETER OF IN
CLAY TO SILT COBBLES
GRAVEL 55 % SAND
LIQUID TIMIT
SAMPLE OF: Sllty Sondy Grov6l
53%
PLASTICITY INDEX
SILT AND CLAY 12 %
FROM:BorlnglO5'
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rqmpl.s vhlch v.r. lcllad. Thr
lcsllng ruporl sholl nol b. rcproduccd,
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qpprcvql of Kumqr & Assoclotcs, lnc,
Sl.vc onolytl! lasllng ls p.rtom.d ln
occordonci wllh ASTM D69t5, ASTM D7926,
ASTM C156 ond,/or ASTM D11,10,
SIEVE ANALYSISHYDROMETER ANALYSIS
f,YE RilDING
24 HS 7 HRS
U.S. STAXD RD SERIES
al rt
CLEAR SQUARE OPEIIINOS
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tl r " i rl r
SAND GRAVEL
FINE COARSEFINEMEDTUM ICOARSE
22-7 -1 15 Kumar & Associates GRADATION TEST RESULTS Fig. 3
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Xmrar & Associatc, he.*
Geotechnical and Materials Engineen
and Fnyironrnental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Silty Sandy Gravel
Sand and Silt
SOIL TYPE
Sand and Silt
(osfl
UNCONFINED
COMPRESSIVE
STRENGTH
lolol
PLASTIC
INDEX
ATTERBERG LIMITS
lolol
LIQUID LIMI'T
,52
2I
47
PERCENT
PASSING NO.
200 stEvE
SAND
l'tt
33
(%)
GRAVEL
55
6.1 90
90
NATURAL
DRY
DENSITY
(ocfl{%l
NATURAL
MOISTURE
CONTENT
1.3
3.8
(ftt
DEPTH
2%
5
2Y)
I
aJ
SAMPLE LOCATION'
BORING
No.22-7-115