HomeMy WebLinkAboutSubsoil Study for Foundation Design 05.31.2024I(hA Kumal & Associates, lnc."
Geotechnical and Materials Engineers
and Environmental Scientists
An Employee Owned 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 Looations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
May 3I,2024
Justin Mahaffey
4865 County Road 309
Parachute, Colorado 8 1 635
jmahaffey@tenaep.com
BtRE-UE-2tF8153
Project No.24-7-297
Subject:Subsoil Study for Foundation Design, Proposed Shop Building,-4865 County
Road 309, Garfield County, Colorado
Dear.Tustin:
As requested, Kumar & Associates performed a subsoil study for design of foundations at the
subject site. The study was conducted in accordance with our agreement for geotechnical
engineering services to you dated May 70,2024. The data obtained and our recommendations
based on the proposed construction and subsurface conditions encountered are presented in this
report.
Proposecl Construction: The proposed shop building r,vill be a one-story steel frame and metal
structure located on the site in the area of the exploratory pits shown on Figure 1. Ground floor
is planned to be monolithic slab-on-grade with thickened edges. Cut depths are expected to
range between about 2 to 3 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 subject site is developed r,vith a single-story residence r,vith several
outbuildings as shor,vn on Figure 1. The building area is vegetated r,vith grass and r,veeds, and
appears to be sloping gently solvn to the southeast. The slope north of the building area is very
steep dor,vn to the nofthr,vest.
Subsurface Conclitions: The subsurface conditions at the site r,vere evaluated by excavating
tr,vo exploratory pits at the approximate locations shor,vn on Figr"rre 1. The logs of the pits are
presented on Figure 2. The subsoils encountered, belor,v about/z foot of topsoil, consist of stiff,
Mahaffw,Justin
0etached Shnp E 4885 ER 309, hrachute
Par#273383011033
a
slightly clayey sand and silt down to the pit depths of 10 feet. Results of swell-consolidation
testing performed on relatively undisturbed samples of the sand and silt soils, presented on
Figure 3, indicate low compressibility under existing moisture conditions and light loading and
a minor collapse potential when wetted under light loading. The samples showed moderate
compressibility when loaded after wetting. The laboratory testing is summarized in Table 1.
No free water was observed in the pits at the time of excavation and the soils were slightly moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we believe spread footings placed
on the undisturbed natural soil designed for an allowable bearing pressure of 1,500 psf can be
usedforsupportoftheproposedstructurewithsomeriskofsett1ement.a,'ffi
bearing pressure of 1,500 psf can be used for a thickened slab foundation design. The soils tend
to compress after wetting and there could be some post-construction foundation settlement if the
bearing soils were to become wetted.
Footings should be a minimum width of 18 inches for continuous walls and2 feet for columns.
Loose and disturbed soils encountered at the foundation bearing level within the excavation
should be removed and the footing bearing level extended dor,vn to the undisturbed natural soils,
and the subgrade should be moistened and compacted. Exterior footings should be provided
r,vith adequate cover above their bearing elevations for frost protection. Placement of footings at
least 36 inches belor,v the exterior grade is typically used in this area. Continuous foundation
r,valls should be reinforced top and bottom to span local anomalies such as by assuming an
unsupported length of at least 12 feet. A thickened slab foundation should be r,vell reinforced
r,vith both transverse and longitudinal steel. Ground insulation should be provided at the exterior
of the perimeter tumed dor,vn sections of the slab foundations and beyond the foundation (at
bearing level) a minimum 3 feet. Foundation r,valls acting as retaining structures, if any, should
be designed to resist a lateral earth pressure based on an equivalent fluid unit r.veight of at least
50 pcf for the on-site soil as backfill.
Fioor Slabs: Tlie natuial on-site soils, exclusive of topsoil, are siiiiable to suppoit lightly loaded
slab-on-grade construction. To reduce the effects of some differential movement, non-structural
floor slabs should be separated from all bearing r,valls and columns r,vith expansion joints r,vhich
allor.v 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
Kumar & Associates, lnc. @ Project No. 24-7-297
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established by the designer based on experience and the intended slab use. A minimum 4-inch
layer of sand and gravel base course should be placed immediately beneath ground level slabs
for support. This material should consist of minus 2-inchaggregate with less lhan50Yopassing
the No. 4 sieve and less than l2Yo passing the No. 200 sieve.
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 soils devoid of vegetation, topsoil and oversized rock.
Underdrain System: An underdrain system should not be required for the proposed slab-on-
grade construction with adequate compaction of foundation backfill and positive surface
drainage is provided away from foundation walls.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the building 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 95oh of the maximum standard Proctor density in pavement and slab areas
and to at least 90o/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 6 inches in the first 10 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in pavement and r,valkway areas.
4) Roof downsponts and drains should discharge r,vell beyond the limits of all
backfill.
5) Landscaping r,vhich requires regular heavy irrigation should be located at least
10 feet from the building. Consideration should be given to the use of xeriscape
to limit potential r,vetting of soils below the foundation caused by inigation.
Limitations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this arca at this time. We make no r.vananty 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 I
Kumar & Associates, lnc. @ Project No. 24-7-297
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and to the depths shown on Figure 2,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 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 reporto 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 cliont for design purposes. We are
not responsible for technical interpretations by others of ow information. As the project evolves,
we should provide continued consultation and field services during sonstruction 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
of excavations and foundation bearing strata and testing of structural fill by a representative of
the geoteohnical engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respeotfu lly Submitted,
Kurnar & Assoclates, lne.
James H. Parsons, P. E.
by:
David A. Y
JHPikac
attachments
P.E.
Figure I * Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Swell-Consolidation Test Results
Table I - Summary of Laboratory Test Results
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Kumar & Associales, lnc. @ Project No. 24"7-297
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4865 COUNTY ROAD 309
0 0 50 100
APPROXIMATE SCALE_FEET
24-7 -297 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
PIT 1
EL. 101 .5'
PIT 2
EL. 100.4'
o (o)(6)0
Ftdtd
LL
I-F(L
Lilo
WC=10.3
DD= 1 03
WC=9.4
DD=95
-2OO=54
FtJ
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t!o
E 5
WC=6.7
DD=94
10
WC=3.1
DD=85
-2OO=49
10
LEGEND
(6)TOPSOIL; SLIGHTLY SANDY, SLIGHTLY GRAVELLY SILT, WITH ROOTS AND ORGANICS, FIRM,
SLIGHTLY MOIST, MEDIUM TO LIGHT BROWN. THICKNESS IN INCHES SHOWN IN PARENTHESES
TO LEFT OF THE LOG.
SAND AND SILT (SM-ML); SLIGHTLY CLAYEY, STIFF, SLIGHTLY MOIST, TAN
F
HAND DRIVE SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON MAY 13, 2024.
2, THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE FIGURE 1 SITE PLAN.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL AND REFER TO
THE BENCHMARK ON FIG. 1.
4. THE EXPLORATORY PIT 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 PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
Wc = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140)
24-7 -297 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
lir
SAMPLE OF: Sond ond Silt
FROM:Pit1@5'
WC = 1O.3 %, DD = 105 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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SAMPLE OF: Sond qnd Sill
FROM:Pit2@6'
WC = 6.7 %, DD = 94 pcf
Consolidotion testing pedormed in
occordonca with NTM D-4546.
full, vithout ths vdtt€n opprovol of
Kuhor ond A$ociot6, lnc. Swell
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
24-7 -297 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig.5
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.24-7-297
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
NATURAL
DRY
DENSITY
GRADATION LIMITS
PIT DEPTH
GRAVEL
%t
SAND
t:/"\
PERCENT
PASSING NO.
200 slEvE
LIQUID LIMIT PLASTIC
INDEX
UNCONFINED
COMPRESSIVE
STRENGTH SOIL TYPE
1
-)10.3 103 Sand and Silt
9 3.i 85 49 Sand and Silt
2 1J 9.4 95 54 Sand and Silt
6 6.7 94 Sand and Silt