HomeMy WebLinkAboutSubsoil StudyI Crt g;çlå.tr¡;f'$fr ,1nf;å *.*
An Employca Owncd Compony
5020 Counfy Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenu'ood@kumarusa.com
r.l'u'w.kunrarusa. com
Office Locations: Denver (HQ), Palker, Cololado Springs, Fort Collins, Glenwood Springs, and Surnmit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED STEEL BUILDING
SHAW PROPERTY
1773 COUNTY ROAD 24I
GARFIELD COUNTY, COLORADO
PROJECT NO. 20-7-528
ocToBER 15,2020
PREPARED FOR:
GENERALANDPRO
ATTN: GABRIEL MICHAEL
P.O. BOX 133022
DALLAS' TEXAS 75313
generalandpro@gmail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION .
SITE CONDITIONS.
FIELD EXPLORATION..
SUBSURFACE CONDITIONS .
FOTINDATION BEARING CONDITIONS ....
DESIGN RECOMMENDATIONS ............
FOUNDATIONS
FOLINDATION AND RETAINING WALLS
FLOOR SLABS
TINDERDRAIN SYSTEM
SURFACE DRAINAGE....
LIMITATIONS
FIGURE I - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS
FIGURE 5 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Associates, lnc. @ Project No. 20.7.528
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed steel building to be located at
7773 County Road 247, Garfteld County, Colorado. The project site is shown on Figure l. 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
Generalandpro dated September 15, 2020.
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 building will be a one- or two-story steel-framed metal structure, 40 feet by 50 feet
in plan view. Ground floor will be slab-on-grade. Grading for the structure is assumed to be
relatively minor with cut depths up to about 4 fo 5 feet. We assume relatively light to moderate
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 proposed building area is currently vacant. There is an existing residence uphill and to the
west of the proposed building area. Topography at the site is valley bottom with moderate slopes
down to the east. Vegetation at the site consists of native grass and weeds. East Elk Creek is
about 150 feet to the east of the proposed building area.
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FIELD EXPLORATION
The field exploration for the project was conducted on October 2,2020. 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 were taken with a 2-inch I.D. spoon sampler. The sampler was driven
into the subsoils at various depths with blows from a 14O-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, Fìgure 2. The samples were returned to our
laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurlace conditions encountered at the site are shown on Figure 2. The
subsoils consist of about Yz foot of topsoil overlying up to 27lz feet of slightly sandy to sandy
clay and silt with scattered gravel underlain by relatively dense, silty sand and gravel in
Boring 1. Boring I was drilled to a depth of 3l feet and Boring 2 was drilled to a depth of
27 feet.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and gradation analyses. Results of swell-consolidation testing perfonned on
relatively undisturbed drive samples of the sandy clay and silt soils, presented on Figure 4,
indicate low to moderate compressibility under conditions of loading and wetting and a minor
expansion potential when wetted under a constant 1,000 psf surcharge. Results of gradation
analyses performed on a small diameter drive sample (minus I%-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 borings at the time of drilling at depths of 17 and 18 feet in
Borings 7 and2, respectively. The subsoils were slightly moist to wet with depth.
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FOUNDATION BEARING CONDITIONS
The soils at the sight possess low expansion potential. Spread footings bearing on the natural
soils appear feasible with a low risk of post construction movement. The risk of movement is
mainly if the bearing soils were to become wetted and precautions should be taken to prevent
wetting of the bearing soils. Footings placed on a depth (typically 2 to 3) feet of compacted
structural fill such as CDOT Class 6 aggregate base course could be used to reduce the risk of
post-construction movement. We should further evaluate the expansion potential of the bearing
soils at the time of excavation.
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 with spread footings bearing
on the natural soils or compacted structural fill.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils or compacted structural fîll
should be designed for an allowable bearing pressure of 2,000 psf. Based on
experience, we expect settlementlheave of footings designed and constructed as
discussed in this section will be up to about llz inches.If the footings are placed
on compacted structural fill, we expect settlement of footings to be less than
1 inch.
2) The footings should have a minimum width of 16 inches for continuous walls and
2 feef 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
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lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this report.
The topsoil and any loose or 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.
A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOIINDATION AND RETAINING WALLS
Foundation wa11s 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
cornputed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting
of the on-site soils and at least 45 pcf for backfill consisting of imported granular materials.
Cantilevered retaining structures which are separate from the building and can be 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 and at least 40 pcf for backfill consisting of imported
granular materials.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The
pressures recommended above assume drained conditions behind the walls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
increase the lateral pressure irnposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure buildup behind walls.
Backfill should be placed in uniform lifts and compacted to at least 90Yo of themaximum
standard Proctor density at a moisture content near optirrum. Backfill placed in pavement and
walkway areas should be compacted to at least 950/o of the maximum standard Proctor density.
Care should be taken not to overcompact the backfill or use large equipment near the wall, since
this could cause excessive Tateralpressure on the wall. Some settlement of deep foundation wall
backhll should be expected, even if the material is placed correctly, and could result in distress to
facilities constructed on the backfill.
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Kumar & Associates, lnc. @ Project No. 20.7-528
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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 0.35. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 350 pcf. The
coefficient of friction and passive pressure values recommended above assume ultirnate soil
strength. Suitable factors of safety should be included in the design to limit the strain which will
occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads should be a 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
construction with a low risk of post construction movement. Placing the floor slabs on a depth
(typically about I to 2 feet) of structural fill could be used to reduce the risk of post-construction
movement. 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
tnovement. 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.
All fill materials for support of floor slabs should be compacted to at least 95o/o of maximum
standard Proctor density at a moisture content near optimum. Required hll can consist of the
onsite soils or an imported granular material such as CDOT Class 6 aggregate base course.
LINDERDRAIN SYSTEM
Although free water was encountered during our exploration below the proposed foundation
elevation, it has been our experience in the area where there are clay soils 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.
Kumar & Associates, lnc. @ Project No. 20.7-528
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The drains should consist of rigid PVC 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 1 foot below lowest adjacent finish grade and
sloped at a minimumYzo/o 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 50% passing
the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at
least lYzfeet deep and wrapped in filter fabric such as Mirafi l40N or 160N.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and rnaintained at all
times after the building has been completed:
1) Inundation of the 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 95o/o 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 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 filter 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 lirnits 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 at this time. We make no warranty either express or implied.
The conclusions and recomlrendations 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
Kumar & Associates, lnc. @ Project No. 20-7.528
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in the füture. If the client is concemed 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 appeff 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 infonnation. 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 veriff 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, trnc.
Robert L. Duran, P.E
Reviewed by:
-Ëfu* /.&:L
Steven L. Pawlak, P.E
RLDlkac
cc: ChrisShaw(shgry.drry9á@g¡esil-ga1E)
Kunnar & Associates, lnc. 'i Project No" 20"7,528
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BORING 1
EL. 102.5'
BORING 2
EL. I O6'
0 0
11/12
WC=4.3
DD= 1 06
-2OO=45
13/12
WC=4.9
DD=101
-200=56
5 8/ 12
WC=7.0
DD=l 1 2
15/ 12
WC=5.9
DD=1 10
10 't0
16/ 12 8/ 12
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s/ 12
WC=22.1
DD= 1 07
-200=55
15/ 12
WC='l 5.6
DD=115
-2AO=52
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20 204/ 12 s/ 12
25 25
50 3042/ 12
+4=42
-200= 1 5
35 35
20-7 -528 Kumar & Associates LOGS OF TXPLORATORY BORINGS Fig. 2
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TOPSOIL; SILT AND CLAY, SANDY, FIRM, SLIGHTLY MO|ST, DARK BROWN, ORGANIC.
CLAY AND SILT
DEPTH AT BORIN
REDDISH BROWN.
(CL_ML); SANDY TO VERY SANDY, SCATTERED GRAVEL TO GRAVELLY WITH
G 2, STIFF TO MEDIUM STIFF, SLIGHTLY MOIST TO WET WITH DEPTH,
GRAVEL AND SAND (CM-SV); StLTy, DENSE, WET, MTXED BROWN, ROUNDED ROCK.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
11 /1, DRIVE SAMPLE BLOW COUNT. INDICATES THAT 11 BLOWS OF A 140-POUND HAMMER"''- FALLTNG 30 tNcHES wERE REeUIRED To DRtvE THE sAMpLER 12 tNcHES.
- DEPTH TO WATER LEVEL ENCOUNTERED AT THE TIME OF DRILLING.
---> DEPTH AT WHICH BORING CAVED FOLLOWING DRILLING.
NOTES
THE EXPLORATORY BORINGS WERE DRILLED ON OCTOBER 2, 2O2O WITH A 4_INCH_DIAMETER
CONTINUOUS-FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURTS SHOWN ON THE SITE PLAN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY BOR¡NGS WERE MIASURED BY HAND LEVEL AND REFER
TO END OF CATTLE GUARD SHOWN ON FIG.1 AS 1OO" ASSUMED.
4, THE EXPLORATORY BORING 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 BORING LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER LEVELS SHOWN ON THE LOGS WERE MEASURED AT THE TIME AND UNDER
CONDITIONS INDICAÏED. FLUCTUATIONS IN THE WATTR LEVEL MAY OCCUR WITH TIME.
7, LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);
DD = DRY DENSITY (PCT) (ISTU D2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ISTU OOSIS);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D1 1 4O).
20-7 -528 Kumar & Associates LEGEND AND NOTTS Fig. 3
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SAMPLE OF: Sondy Silt ond Cloy
FROM:Boringl@5'
WC = 7.0 %, DD -- 112 pcl
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
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1.0 APPLIED PRESSURE -100
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1.0 APPLIED PRESSURE - KSF 10 100
SAMPLE OF: Very Sondy Sill ond Cloy
FROM:Boring2@5'
WC = 5.9 %, DD = 110 pcf
These test res!ìts opply only to th€
soñple3 lested. lh€ testÌng repod
sholl not be r€produced, except in
full, without lhe wdtt€n opprovsl ot
ond tusociotes, lnc. Ssell
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
20-7 -528 Kumar & Associates SWTLL-CONSOLIDATION TTST RESULTS Fig. 4
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100
90
ao
70
60
50
40
30
10
o
r0
20
30
40
50
60
70
80
90
100
2.36 200-125 2.O
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT COBBLES
GRAVEL 42 % SAND 43
LIQUID LIMIT
SAMPLE OF: Cloyey, Sìlly, Sond ond Grovel
PLASTICITY INDEX
SILT AND CLAY 15 %
FROM:Boringl@30'
Th€se l€sl resulls opply only lo lhe
sqmp¡os wh¡ch w€re l6sl6d. The
l€sling rgport sholl nol b9 reproduced,
excepl lh full, wllhoul thê wrlll€n
opprovo¡ of Kumor & Assoc¡otos, lnc.
Si€v€ qno¡ysis iosllng ls p€rform€d in
occordonco wllh ASTM 06915, ASTM 07928,
ASTM C136 ond/or ASTM 01140.
SAND GRAVEL
FINE MEDIUM COARSE FIN E COARSE
20-7 -s28 Kumar & Associates GRADATION TTST RTSULTS Fig. 5
l(+rt#ffi¡å'trtffig:i*'""Ë;n'**'TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.20-7-528Silty Sand and ClaySOIL TYPElosf)UNCONFINEDCOMPRESSIVESTRENGTHPLASTICINDEX(%)ATTERBERG LIMITS(%lLIQUID LIMITPERCENTPASSING NO.200 stEVE45SAND%lGRADATION(%)GRAVELNAIURALDRYDENSITY(pcfl1064.3(%)NATURALMOISTURECONTENT(fttDEPTH2t/zSAMPLE LOCATIONBORINGI57.0t12Sandy Silt and Clay1522.110755Very Sandy Silt and Clay30424315Clayey Silty Sand andGravel2.tl /L/24.910156Very Sandy Silt and Clay55.9ll0Very Sandy Silt and Clay15r s.611552Very Sandy Silt and Clay