HomeMy WebLinkAboutSubsoils Report for Foundation DesignI(tA Kumar & Associateg, lnc.@
Geotechnical and Materiais Engineers
and Environmental Scientists
An Ennployoo On*ncd Connpony
5020 County Road 154
Glenrvood Springs, CO 81601
phone: (97Q)94s-1988
far: (970) 945-8454
email : kagler.:wood@kumarulsa.co1ll
u'rvu'.ku trantsa.com
olllce Locations: Denver (HQ), Parker, cciorado springs, Fort collils, Glenwcod Springs, and Sumrnit County, Cnlorado
June 10,2024
Gerald Slafkes
1887 CountyRoad23T
Silt, Colorado 81652
SU:elfw o o d s oo @g$ a{-qg!
Project No.24-7-260
Subject:Update to Subsoil Study, Proposed Shop Building, 1887 County Road237,
Garfield County, Colorado
Dear Gerald:
As requested, Kumar & Associates is providing an update to our recent subsoil study dated
May 20,2y24,project No.24-7-260. This update is for the previous proposed shop to include an
auxiliary dwelling unit (ADU) for a second story of the previous proposed building at the subject
site. This letter provides our up-dated foundation design recommendations. The services are
supplemental to our agreement for geotechnical engineering services to Gerald Slafkes dated
April 23,2024.
The proposed shop building/ADU will be a two-story structure with a slab-on-grade ground
floor. The first story will be a unconditioned shop space and the second story will be
conditioned living area. Grading for the structure is assumed to be relatively minor with cut
depths between about 4 to 6 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.
It is our understanding that you would like recommendations for placing a spread footing
foundation on structural fill. Provided below are recommendations for spread footings bearing
on compacted structural fill.
Spread Footings: Considering the subsurface conditions encountered in the exploratory boring
and the nature of the proposed construction, we believe the proposed building can be founded
with spread footings bearing on at least 3 feet of compacted structural fill with some risk of
settlement. Structural fill can consist of the on-site soils devoid of topsoil, organics and debris,
or a suitable imported granuldr material such as CDOT Class 6 aggregate base course.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
_N
s
1)Footings on at
allowable bearing pressure a{aq0oi$-j9sed on experience, we expect initial
settlement of footings designed and constructed as discussed in this section will
be about I inch or less. Some additional settlement could occur if the bearing
Gerald Slafkes
June 10,2024
Page2
3)
soils were to become wetted. The magnitude of additional movement would
depend on the depth and extent of additional wetting but could be on the order of
Yzto I inch.
The footings should have a minimum width of 18 inches for continuous walls and
2 feet for isolated Pads.
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.
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 actingas retaining structures should also be designed to resist a
lateral earth pressure oolresponding to an equivalent fluid unit weight of at least
55 pcf.
All topsoil, existing fill and the required depth of natural soils to provide 3 feet of
structural fill, 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. Structural fill
below footing areas should extend l% feetbeyond the edges of the footings and
be cornpacted to at least 98o/o standard Proctor density at a moisture content near
to slightly above optimum.
A representative of the geotechnical engineer should observe all footing
excavations and test structural fill compaction on a regular basis prior to concrete
placement to evaluate bearing conditions.
4)
Other recommendations in our previous report should also be observed. We should be advised
of any variations encountered in the excavation conditions for possible changes to
recommendations contained in this letter.
If you have any questions or need further assistance, please call our office'
2)
s)
6)
Sincerely,
Kumar & Associatesn
James H. Parsons,
JHPlkac
Kumar & Associates, lnc' @ Project No.24-7-260
T(lA Kumar & Associates, lnc.'
Geotechnical and Materials Engineers
and Environmental Scientists
An Employcc Owncd Compony
5020 County Road 154
Clenwood Springs, CO 8160 I
phone: (970) 945-7988
fax: (970) 945-8454
enrai I : kaglenwood@kunrarusa.col'l'r
wrvw.kumamsa.cour
Oflicel-ocations: Denver(lJQ).Parker'.CololadoSprings"IrortCollins.Glertri,oodSplings.andSuntntitCountl"Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED SHOP BUILDING
1887 COUNTY ROAD 237
GARFIELD COUNTY, COLORADO
PROJECT NO.24-7-260
MAY 20,2024
PREPARED FOR:
GERALD SLAFKES
1887 COUNTY ROAD 237
sILTo COLORADO 81652
smallwoodsco@gmail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION ..
SITE CONDITIONS..
FIELD EXPLORATION.
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS ..
FOTINDATIONS
FLOOR SLABS
UNDERDRAIN SYSTEM
SURFACE DRAINAGE...
LIMITATIONS..
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2 . LOG OF EXPLORATORY BORING
FIGURE 3 - SWELL-CONSOLIDATION TEST RESULTS
TABLE 1. SUMMARY OF LABORATORY TEST RESULTS
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1
1
1
a
2
2
aJ
4
4
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Kumar & Associates, lnc. @ Project No. 24-7-260
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed shop building to be located at
1887 County Road 237, 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 Gerald
Slafkes dated April 23,2024.
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 and laboratory testing were analyzedto 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 shop will be a tall single-story structure with slab-on-grade ground floor located at
the exploratory boring shown on Figure 1 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 two single-story residences atthe time of our field
exploration. The ground surface was gently sloping down to the southeast at grades estimated
at between 5 and 10 percent. Vegetation consists of deciduous trees with an understory of grass
and weeds. The farmers irrigation ditch runs along the west side of the property.
F'IELD EXPLORATION
The field exploration for the project was conducted on May 7,2024. 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-45B
drill rig. The boring was logged by a representative of Kumar & Associates, Inc.
Samples of the subsoils were taken with 1%-inch and 2-inchl.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.
Kumar & Associates, lnc. @ Project No, 24-7-260
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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 Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory
for review by the project engineer and testing.
SUBSURFACE CONDITIONS
A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The
subsoils consist of about t/zfoot of topsoil overlying stiff sandy silt to about 4 feet deep where
medium dense clayey sand was encountered down to 27 feet deep. Below the sand a hard layer
was encountered to the maximum explored depth of 28 feet. Our experience in the area indicates
this layer could be claystone/siltstone bedrock. Drilling in the bedrock with auger equipment
was difficult due to its hardness and drilling refusal was encountered in the deposit.
Laboratory testing performed on samples obtained from the boring included natural moisture
content and density and finer than sand grain size gradation analyses. Results of swell-
consolidation testing performed on relatively undisturbed drive samples, presented on Figure 4,
indicate low to moderate compressibility under conditions of loading and wetting. The
laboratory testing is summarizedin Table l.
No free water was encountered in the boring at the time of drilling and the subsoils were slightly
moist to moist.
F'OUNDATION BEARING CONDITIONS
The upper fine-grained soils encountered in the boring possess low bearing capacity and low
to moderate settlement potential especially when wetted under load. The underlying bedrock
should possess relatively high bearingcapacity andtypically low settlement potential. The
proposed shop building can be supported on lightly loaded spread footings bearing on the upper
soils with a risk of foundation movement possibly resulting in distress to the building. The risk
of movement will be increased if the bearing soils become wetted and precautions should be
taken to prevent wetting. A lower risk option would be to place a depth (typically 3 feet) of
structural fill below the footings or extending the bearing level down to the underlying bedrock
with a deep foundation system such as drilled piers or helical piers. Provided below are
recommendations for spread footings bearing on the natural soils. If structural fill or a deep
foundation system are proposed, we should be contacted to provide additional recommendations.
DESIGN RECOMMENDATIONS
FOL]NDATIONS
the proposed construction, the building can be founded with spread footings bearing on the upper
natural soils with a risk of settlement.
Kumar & Associates, lnc. @ Project No. 24-7-260
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The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the upper 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
1 inch or less. There could be additional post-construction settlement if the
bearing soils become wetted. The magnitude of additional settlement would
depend on the depth and extent of the wetting but could be on the order of I inch.
2) The footings should have a minimum width of 18 inches for continuous walls
and2 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
atea.
4) Continuous foundation walls should be heavily reinforced top and bottom to
span local anomalies and resist differential movement such as by assuming an
unsupported length of at least 14 feet. Foundation walls acting as retaining
structures should also be designed to resist a lateral earth pressure coffesponding
to an equivalent fluid unit weight of at least 55 pcf.
5) The topsoil and any loose disturbed soils should be removed and the footing
bearing level extended down to the firm natural soils. The exposed soils in
footing area should then be moistened and compacted.
6) A representative ofthe geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade
construction. To reduce the effects of some differential movement, 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 should be placed beneath slabs for support. This material should
consist of minus 2-inch aggregate with at least 50oh retained on the No. 4 sieve and less than
l2o/o passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95o/o of maximum
ty ata sture neat o
on-site soils devoid of vegetation, topsoil and oversized rock.
Kumar & Associates, lnc. @
can
Project No. 24-7-260
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TINDERDRAIN SYSTEM
It is our understanding 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
experience in the areathat local perched groundwater can develop during times of heavy
precipitation or seasonal runoff. Frozen ground during spring runoffcan 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
Providing and maintaining proper surface drainage will be critical to the long-term satisfactory
performance of the proposed shop building. 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 90Yo 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.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy inigation 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 inigation.
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
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
Kumar & Associates, lnc. @ Project No, 24-7-260
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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.
This report has been prepared for the exclusive use by our client for design pu{poses. 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 veri$ 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, I
James H. Parsons, P
Reviewed by:
Steven L. Pawlak, P.E.
JHPlkac
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58663
Kumar & Associates, lnc, o Project No.24-7-260
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1887 COUN ROAI-)237
50 0 100
APPROXIMATE SCALE_FEET
Fig 1LOCATION OF EXPLORATORY BORING24-7 -260 Kumar & Associates
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4..
BORING 1
EL. 95.8'
LEG END
TOPSO|L; SILT, SANDY, 0RGANICS, FIRM, MO|ST, BR0WN.
0
8/12
V'lC=l4.2
DD=8 1
SILT (ML); SANDY T0 VERY SANDY, STIFF, SLIGHTLY MOlsT T0
MOIST, TAN.
15/ 12
WC=7.6
-200=35
SAND
DENSE
(SC); CLIYTY, SCATTERED GRAVEL, LOOSE TO MEDIUM
, SLIGHTLY MOIST TO MOIST, LIGHT BROWN TO BROWN
5
CLAYST0NE/SILTST0NE; VERY HARD, M0|ST, GRAY BROWN.
DRIVE SAMPLE, 2_INCH I.D. CALIFORNIA LINER SAMPLE.
10
18/12
i DRIVE SAMPLE, 1 5/8-|NCH r.D. SPL|T SP00N STANDARD
PENETRATION TEST.
FtJt!
LL
IIF
o_
Ldo
s717DR|VE SAMPLE BLOW C0UNT, INDICATES THAT I BLOWS 0F-, .-A
14o-POUND HAMMER FALLING 50 INCHES WERE REQUIRED
15
7/12
WC='1 0.3
-200=36
TO DRIVE THE SAMPLER 12 INCHES.
PRACTICAL AUGER REFUSAL.t
NOTES
20 1 THE EXPLORATORY BORING WAS DRILLED ON MAY 7, 2024 WIIH
A 4-INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER.
2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED
APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE
SITE PLAN PROVIDED.
25
13/12
WC=16.4
DD=1 1 0
3. THE ELEVATION OF THE EXPLORATORY BORING WAS MEASURED
BY HAND LEVEL AND REFER TO THE TOP OF THE EXISTING
GARAGE SLAB AS AN ASSUMED 1OO' BENCHMARK.
4. THE EXPLORATORY BORING LOCATION AND ELEVATION SHOULD BE
CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE
METHOD USED.
30 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY
BORING LOG REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN
MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL,
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE
TIME OF DRILLING,
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSTTY (pcf) (lSrV O ZZ1O);
-2OO = PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140)
Fi1. 2Kumar & Associates LOG OF EXPLORATORY BORING24-7 -260
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SAMPLE 0F: Cloyey Sond
FROM:Boringl @24'
WC = 16.4 ?(, DD = 110 pcf
Th€teeted,
not be r€produc.d,
without the wdlten opprovol of
ond Associdtes, lnc, Sw.ll
in
NO MOVEMENT UPON
WETTING
2
x
JJ
Lrl
=a
I
z.o
F
o
-lo
@z.oo
0
-2
-4
-6
-8
-'t 0
1.0 RE - KSF 10 100
Fig. 324-7 -260 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS
Sandy Silt
Clayey Sand
Clayey Sand
Clayey Sand
SOIL TYPE
(osfl
UNCONFINED
COMPRESSIVE
STRENGTH
(%l
PLASTIC
INDEX
ATTERBERG LIMITS
(ol
LIQUID LIMIT
35
36
PERCENT
PASSING NO.
200 stEVE
SAND
(Yol
GRADATION
(%l
GRAVEL
110
(ocfl
NATURAL
DRY
DENS]TY
1814.2
7.6
10.3
16.4
Plol
NATURAL
MOISTURE
CONTENT{
2
4
41
24
(ft)
DEPI
SAMPLE LOCATION
BORING
1
rcn & Associates, lnc.@
nical and Materials Engineers
Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Proiect No.24-7-260