HomeMy WebLinkAboutSubsoils Study for Foundation DesignI .*rt u,ffi,ffit##l'ur'{s;;*'"
An Employse Orncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970)945-7988
fax: (970) 945-8454
ernail : kaglenwood@kumarusa.com
www.kumarusa.com
Offrce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED STEEL BUILDING
111 WEST MAIN STREET
SILT, COLORADO
PROJECT NO. 24-7-320
JUNE 11,2024
PREPARED FOR:
ANDREW RE,EVES
P.O. BOX 1198
SILT, COLORADO 81652
an drew@reeveselectric. com
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PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
ET'FE T'r\NTT\TTTr\\TEpr r L vvlfulllvllu
FIELD EXPLOR.ATION
SIIB SURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS ....................
FOUNDATIONS
FOUNDATION AND RETAINING WALLS
FLOOR SLABS
UNDERDRAIN SYSTEM .............
SI]RFACE DRAINAGE...............
LIMITATIONS
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2 - LOG OF EXPLORATORY BORING
FIGURES 3 and 4 - SWELL-CONSOLIDATION TEST RESULTS
FIGURE 5 - GRADATION TEST RESULTS
TABLtr i- STIMMARY OF LABORATORY TEST RESULTS
1-
1
1I
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..................- 2
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..................- 3
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..................- 5
5
Kumar & Associates, lnc. @ Project No. 24-7-320
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed steel building to be located at
111 West Main Street, Silt, 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 Andrew Reeves dated
May 17,2024.
An exploratory boring was drilled 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 andlaboratory testing were analyzedto develop recommendations for
foundation typcs, dcpths 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 steel building will be a tall single-story metal frame structure. Ground floor will
be slab-on -grade. Grading for the structure is assumed to be relatively minor with cut depths
between about 2 to 4 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 subject site was developed with an existing residnece and shed at the time of our field
exploration, The ground surface was relatively flat. Vegetation consists of grass and weeds in
the front of the site and was barren in the rear of the site. There was evidence of minor surface
grading and some debris on the surface.
FIELD EXPLORATION
The field exploration for the project was conducted on May 31,2024. One exploratory boring
was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The boring
was advanced with 4-inch diameter continuous flight augers powered by a truck-mounted CME-
55 drill rig. The boring was logged by a representative of Kumar & Associates, Inc.
Samples of the subsoils were taken with l%-inch and 2-inch LD. spoon samplers. The samplers
were driven into the subsoils at various depths with blows from a 140-pound hammer falling 30
Kumar & Associates, lnc. @ Project No. 24-7-320
-2-
inches. This test is similar to the standard penetration test described by ASTI\4 Method D-1586.
The penetiation 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 Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory
for review by the project engineer and testing.
SUBSLTRFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about 32%fee!" of sandy silty clay cverlying dense, siity sandy gravei and
cobbles to the maximum drilled depth of 34 feet.
Laboratory testing performed on samples obtained from the boring included natural moisture
content and density and gradation analysis. Results of s-well-consolidation testing performed on
rela-tively un-distr-rrbed drive samples, presented on Figures 3 and 4, rndicate low to moderate
compressibility under existing low moistnre conditions and light loading and low collapse or low
swell potential when wetted under constant light surcharge. Results of a gradation analysis
performed on small diameter drive samples (minus l%-inch fraction) of the coarse granular
subsoils are shown on Figure 5. The laboratory testing is summarized in Table 1 .
Free water was encountered in the boring at a depth of 3l% feet at the time of drilling and the
subsoils were slightly moist to moist above the grourrd water level.
FOUNDATION BEARING CONDITIONS
The shallow clay soils encountered in the boring possess low bearing capacity and low to
moderate settlement potential especially when wetted under load. The underlying gravel soils
possess moderate bearing capacity and typically lo-w settlemeni potential. The proposed steel
building can be founded with spread footings bearing on the natural soils with a risk of
settlement especiaiiy if thc bcaring soiis become wetted. A lower risk option wouid be to
provide a depth of structural fill, typically about 4 feet, below foundation areas. Alternatively
a deep foundaiion systein such as helical piers can be used to extend ttre bearing ievel down io
the underlying dense granular soils. Provided below are recommendations for a spread footing
fnrrdnatinn srrsfern hecrino nn thenafrrrql cnilc Tf rpnnmmenrlqfinnc fnr ctrrrchrrql fill nr q rlepn
foundation system are desired, we should be contacted to provide them.
DESIGN RECOMMENDATIONS
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the proposed construction, the building can be founded with spread footings bearing on the
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Kumar & Assoclates, lnc. o Project No. 24-7-320
-3-
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 1,200 psf. Based on experience, we expect initial
settlement of footings designed and constructed as discussed in this section will
be about I inch or less. Additional, post-construction, settlement could occur if
the bearing soils become wet. The magnitude of additional settlement would
depend on the depth and extent of wetting but could be on the order of about I to
lY' inches.
Z) The footings should have aminimum width of 18 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 fypically used in this
area.
4) Continuous foundation walls should be heavily reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least T4 feet.
Foundation walls acting as retaining structures should also be designed to resist
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this rePort'
5) All existing fill, topsoil and any loose disturbed soils should be removed and
the footing bearing level extended down to the relatively firm natural soils. The
exposed soils in footing area should then be moistened and compacted. If water
seepage is encountered, the footing areas should be dewatered before concrete
placement.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOUNDATION AND RETAINING WALLS
Foundation walls and retaining structures which are laterally supported and can be expected to
undergo only a slight amount of deflection should be designed for a lateral earth pressure
computed on the basis of an equivalent fluid unit weight of at least 60 pcf for backfill consisting
of the on-site fine-grained soils. Cantilevered retaining structures which are separate from the
building and canbe expected to deflect sufficiently to mobilize the full active earth pressure
condition should be designed for a lateral earth pressure computed on the basis of an equivalent
fluid unit weight of at least 50 pcf for backfill consisting of the on-site soils.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, trafftc, construction materials and equipment'
Kumar & Associates, lnc. o Project No. 24-7-320
-4-
The pressures recommended above assume drained conditions behind the waiis and a horizontal
backfiii sufface. The buiitiup of water behinci a waii or an upwarii sioping backfiii surface wiii
increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure buildup behind waiis.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor densi[r at a moisture content slightly above optimum. Backfill placed in
pavement and walkway arsas should be compacted to at least 95o/o of the maximum standard
Proctor density. Care should be taken not to overcompact the backfill or use large equipment
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deep foundation wall backfill should be expected, even if the material is placed correctly, and
could result in distress to facilities constructed on the backfill.
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resistance of the footing on the foundation materials and passive earth pressure against
the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated
based on a coefficient of friction of 0.40. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 325 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 uitimate strength, particuiariy in the case of passive resistance. Fili placed against
tlre sides of the footings to resist lateral loads should be compacted to at least 95o/o of the
maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade
construc{.irtn. T,r reduce the effects of some differentiai movement, floor slabs should be
separated from all bearing waiis anci columns with expansion loints which aiiow unrestrained
vertical movement. Floor slab controljoints should be used to reduce damage due to shrinkage
cracking. The requirements for joint spacing and slab reinforcement shouiri be estabiished by the
designer based on experience and the intended slab use. A minimum 4-inch layer of relatively
we!! graded sand and gravel should be placed beneath slabs-on-gradc to facilitate drainage. This
material should consist of minus 2-inch aggregate with at least 50o/o retained on the No. 4 sieve
and less than l2oh passing the No. 200 sieve.
All f,tll materials for support of floor slabs should be eompacted to at least 95Yo of maximum
standard Proctor density at a moisture oontent near optimum. Required fiIl can oonsist of the
on-site granuiar soils devoiri of vegetation, topsoii and oversized rock.
Kumar & Associates, lnc. 0 Project No.24.7-320
-5-
UNDERDRAIN SYSTEM
The proposed shallow foundations should not need a perimeter foundation drain, provided that
the exterior foundation wall backfill is well-compacted and good surface drainage, as described
below, is maintained around the shop.
SURFACE DRAINAGE
Providing and maintaining proper surface drainage around the proposed building will be critical
to the long-term satisfactory performance of the proposed residence. 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 95Yo 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 paved areas. Free-draining wall backfill should be
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
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 boring drilled at the location indicated on Figure 1, the proposed type of
construction and our experience in the arca. 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 boring 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. 24-7-320
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This report has been prepared for the exclusive use by our client for design purposes. We are not
*^.*^---.:!-!^q^-a^^!--:^-1 .l--r^*--t^tl- .--1--- ^a1--,-- ^.c- -- --'-- f- ,Lr- a ar- ,r -L t -reDPUuDrulE t-ur rrrulll[u&rr rurt'{Prslallolts Dy ourers or our inlorrnauon. As rng proJgcE cvoives, wc
should provide continued consultation and freld services during construction to review and
monitor the implernentation of our recolnmendatiorrs, and io verify that the recomrrr.endations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recommendaiions presented herein. We recommend on-site observation
of excavations an<i foundation bearing strata anri testing of structurai fiii by a representative of
the geotechnical engineer.
Respectfuiiy Submitte<i,
Kuman & Assoeictes,
James H. Parsons, P
Reviewed by:
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Daniel E. Hardin, P.E.
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24-7 -320 Kumar & Associates LOCATION OF EXPLORATORY BORING Fig. 1
BORING 1 LEUENU
CLAY (CL); SANDY, SILTY, STIFF TO VERY STIFF,
qCATTFRFN GRAVFI M6IqT T6 WFST WITH RFPTI.]
BROWN
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WC= 1 1.9
DD= 1 08
GRAVEL (oU); snu0v, SILTY, COBBLES, DENSE, wET,
BROWN
q DRIVE SAMPLE, 2_INCH I.D. CALIFORNIA LINER S,AMPLE.
17 /12
WC= 1 2.8
DD= 1 03 I DR|VE SAMPLE, 1 3/8-|NCH r.D. SPLIT SP00N STANDARD
PINITRATION TEST.
10
12/12
hht\rF arr/nt T hl ntr, ^nttttT t\tht^lTTc TttlT 4 7 hr nrrr- At42 114 U^llL JAMTLL oLvlt UvUl\ l. ll\UIUAILJ lnAl lJ trLVWJ Uftrl tL A 14o-pouND HAMMER FALLTNG 30 TNCHES WERE REQUIRED
TO DRIVT THT SAMPLTR 12 INCHES,
0 oeptH To wATER LEVEL ENcoUNTERED AT THE TIME oF= DRILLING,
-.-> DEPTH AT WHICH BORING CAVED,
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WC=15.5
DD=1 1 0
-200=92
NOTES
1 THE EXPLORATORY BORING WAS DRILLED ON MAY 31, 2024 WITH
A 4-INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER.FLI
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17 /12
WC= 1 7.5
DD= 1 08
2, THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED
APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE
SITE PLAN PROVIDED.
3. THE ELEVATION OF THE EXPLORATORY BORING WAS NOT
MEASURED AND THE LOG OF THE EXPLORATORY BORING IS
FLOIITI] IO DEPTH.
25
13/12 4. THE EXPLORATORY BORING LOCATION SHOULD BE CONSIDERED
ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE TXPLORATORY
BORING LOG REPRESENT THE APPROXIMATI BOUNDARIES BITWEEN
MATERIAL TYPTS AND THE TRANSITIONS MAY BE GRADUAL.
30
11 /12
6. GROUNDWATER LEVEL SHOWN ON THE LOG WAS MEASURED AI
THE TIME AND UNDIR CONDITIONS INDICATED. FLUCTUATIONS IN
THE WATER LEVEL MAY OCCUR WITH TIME.
35
30/6, 20/o
WC= 1 8.7
*4=32
-200=3 1
7. I.ABORA.TORY TEST RESULTS:
WC = WATER OONTENT (%) (ASTM D 2216);
DD = DRY DENSTTY (pcf) (lSrU O ZZ1O);
+4 = PERCENTAGE RETAINED ON NO.4 SIEVE (NSTU O OSiS);
-200 = PEROENTAGE PASSING N0. 200 SIEVE (ASTM D 1140).
40
24-7 -320 Kumar & Associates LOG OF TXPLORATORY BORING Fig. 2
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HYDROMETER ANALYSIS SIEVE ANALYSIS
24 HRS 7 HRS
TIME READINGS
6dMIN I qMIN 4MIN r MrN lli o
to
20
30
40
50
60
70
a0
90
100
100
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2,36 76.2
DIAMETER OF PARTICLES IN MI
2-O
METERS
CLAY TO SILT COBBLES
GRAVEL 32 % SAND
LIQUID LIMIT
SAMPLE OF: SiltY Sond ond Grovel
37%
PLASTICITY INDEX
SILT AND CLAY 31 %
FROM:Boringl@33'
Those lesl results opply only to lh€
somoles which wero l€sl6d. Tho
iesllig report shdll nol b€ reproduced,
exc€Dl in full, wlthoul lh€ writlon
ooorovol of Kumqr & Assoclol€s, lnc.
Siive onolvsls lesllno ls performed ln
occordqnc6 with ASTM 06913, ASTM 07928'
ASTM C136 ond/or ASTM 0t140.
GRAVELSAND
COARSE FINE COARSEMEDIUMFIN E
Fig.5GRADATION TEST RESULTSKumar & Associates24-7 -320
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TABLE 1
SUMMARY OF LABORATORY TEST RESUI.TS
24-7f,z0
1
BORING
TION
-t -t
20
1 5
5
2
DEPTH
18.7
T7.5
15.5
12.8
911
t%l
NATURAL
MOISTURE
COMTENT'
32
108
110
103
108
NATURAL
DRY
DENSITY
GRAVEL
$l
SAND
%t
a-3t J I
92
PERCENT
PASSING NO.
2{}{l SIEVE
(%l
LIQUID LIilIIT
I%l
PLASTIC
INDEX
ATTERBERG LIMITS
losfl
I..[NCONFINED
Cf]MPRESSN/E
STRENGTH
Silfy Sand and Gravel
Sandy Silty Clay
Sanrly Silty Clay
Sandy liilfy Clay
Sandy Silty Clay
SCII- TYPE