HomeMy WebLinkAboutSubsoils Study for Foundation Design¡(ln Kumar & Assoclates, lnc.'
Geotechnical and Materials Engineers
and Environmental Scientists
An Employcc Owncd 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 Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LO"t 3T, TRONBRTDGE PHASE 3
BLUE HERON DRIVE
GARFTELD COUNTY, COLORADO
PROJECT NO.2l-7-434
JUNE 25,,2021
PREPARED FOR:
SCIB, LLC
ATTN: LUKE GOSDA
0115 BOOMERANG ROAD, SUITE 52018
ASPEN, COLORADO 81611
luke.gosda@sunriseco.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION .
SITE CONDITIONS..
GEOLOGY
FIELD EXPLORATION
SUBSURFACE CONDITIONS .
FOUNDATION BEARING CONDITIONS ..
DESIGN RECOMMENDATIONS ...........
FOUNDATIONS
FLOOR SLABS
LINDERDRAIN SYSTEM ....................
SURFACE DRAINAGE...............
LIMITATIONS
FIGURE 1 - 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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1
1
1
.,
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5
5
6
Kumar & Associates, lnc. @ Project No. 2l-7-434
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot3T,Ironbridge Phase 3, Blue Heron Drive, 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 SCIB, LLC dated May 10, 2021.
A field 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, 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 ÞuI
residence were not available at the time of orir study., F
f/æ/ {n be
P/at
or the purposes ofPlans for the proposed
our study the proposed residence is assumed to be a one- or two-story structure over a
crawlspace with an attached slab-on-grade garage located in the upper part of the lot shown on
Figure 1. Ground floors are assumed to be a combination of slab-on-grade and structural over
crawlspace. Grading for the structure is assumed to be relatively minor with cut depths between
about 2 to 3 feet. V/e 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 vacant at the time of our field exploration. The site is split into two
relatively flat benches separated by a relatively steep 8-foot tall slope. The borings were drilled
on the upper bench as shown on Figure 1. Vegetation consists of grass and weeds. The downhill
side of Blue Heron Drive appears to be a fill bench for residence construction placed during the
sub-division develop'ment. The Roarrng Fork River is located about Y¡mlle to the north.
Kumar & Associates, lnc, @ Project No. 21-7-434
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GEOLOGY
The geologic conditions were described in a previous report conducted for planning and
preliminary design of the overall subdivision development by Hepworth-Pawlak Geotechnical
(now Kumar & Associates) dated October 29,1991, Job No. I9l 321. The natural soils on the
lot mainly consist of sandy silt and clay alluvial fan deposits overlying gravel terrace alluvium of
the Roaring Fork River. The river alluvium is mainly a clast-supported deposit of rounded
gravel, cobbles, and boulders typically up to about 2Io 3 feet in size in a silty sand matrix and
overlies siltstone/claystone bedrock.
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Ironbridge subdivision.
These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some
massive beds of gypsum and limestone. Dissolution of the gypsum under certain conditions can
cause sinkholes to develop and can produce areas of localized subsidence. A sinkhole occurred
in the parking lot adjoining the golf cart storage tent in January,2005 located several hundred
feet south of Lot 37 which was backfilled and compaction grouted. To our knowledge, that
sinkhole has not shown signs of reactivation such as ground subsidence since the remediation.
Sinkholes possibly related to the Evaporite were not observed in the immediate area of the
subject lot. Based on our present knowledge of the subsurface conditions at the site, it cannot be
said for certain that sinkholes related to the underlying Evaporite will not develop. The risk of
future ground subsidence on Lot 37 throughout the service life of the proposed building, in our
opinion, is low; however, the owner should be made 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 May 18 and June 14,202I. 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 wilh l%-inch and 2-inch I.D. spoon samplers. The samplers
were 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 \ /ere taken and the penetration resistance values are
Kumar & Associates, lnc, @ Project No,21-7-434
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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 consist of about 4 to 5t/z feet of fill and nil to 3 feet of stiff,, sandy silty clay overlying
dense, slightly silty sandy gravel with cobbles and possible boulders down to the maximum
explored depth of 16 feet. Drilling in the dense granular soils with auger equipment was difficult
due to the cobbles and boulders and practical drilling refusal was encountered in Boring 1.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and gradation analyses. The results of swell-consolidation testing performed
on a sample of natural clay soil, presented on Figure 4, indicate low to moderate compressibility
under conditions of loading and wetting. Results of gradation analyses performed on small
diameter drive samples (minus Il/z-inch fraction) of the coarse granular subsoils are shown on
Figure 5 . The laboratory testing is summari zed in Table 1 .
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to moist.
FOUNDATION BEARING CONDITIONS
Spread footing foundations placed on the relatively dense fill soil or underlying natural soils
should be adequate for support of the proposed residence with relatively low settlement potential
Although the existing f,rll and clay soils can show a minor expansion potential when wetted, our
experience in this area is that the soils are typically not expansive spread footings bearing
entirely on the dense gravel soils with moderate bearing pressure should have a low settlement
risk. The bearing condition of the soils exposed in the excavation should be further evaluated at
the time of construction.
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 relatively dense fill soils or the underlying natural soils if encountered.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
Kumar & Associates, lnc. @ Project No. 21-7-434
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1) Footings placed on the relatively dense fill soils or the underlying natural soils
should be designed for an allowable bearing pressure o4J90 psf. Based on
experience, we expect settlement of footings designed and constructed as
discussed in this section will be about 1 inch or less. Post-construction settlement
could be around lrto I inch mainly if the bearing soils are wetted.
2) The footings should have a minimum width of 18 inches for continuous walls and
2 feet for isolated pads.
-F
3) Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
offoundationsatl.usbelowexteriorgradeistypicallyusedinthis
atea.
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 12 feet.
Foundation walls acting as retaining structures should also be designed to resist a
lateral earth pressure conesponding to an equivalent fluid unit weight of at least
55 pcf for the onsite soils as backfill.
5) Topsoil and any loose disturbed soils should be removed and the footing bearing
level extended down to the relatively dense f,rll soils or natural soil beneath the
f,rll. The exposed soils in footing area should then be moistened and compacted.
Additional structural fill can consist of the onsite soils to atleast9SYo
of density atnear optimum moisture content structural fill
should extend beyond the footing edges a distance equal to at least one-
the fill below the footing.
ve of the engineer should observe all footing
excavations prior to concrete placement to evaluate
FLOOR SLABS
The on-site hll soils or natural 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 road base should be placed beneath garage level slabs. This material should consist of
minus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less than I2Yo passing
the No. 200 sieve.
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Kumar & Associates, lnc. o Project No. 21-7-434
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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 fill can consist of the on-
site fill soils devoid of vegetation, topsoil and oversized rock.
LTNDERDRAIN SYSTEM
The proposed shallow (less than 4 feef) crawlspace and slab-on-grade garage should not have a
perimeter underdrain system provided that the site grading recommendations contained in this
report are followed. We recommend that below-grade construction, such as retaining walls and
basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain
system.
If installed, 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 1 foot below lowest adjacent finish grade and
sloped at a minimum lo/o to a suitable gravity outlet or drywell based in the gravel soils. Free-
draining granular material used in the underdrain system should contain less than 2o/o 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 Ilz feet deep.
SURFACE DRAINAGE
Proper surface grading and drainage will be critical to prevent wetting of the bearing soils and
satisfactory performance of the foundation. The following drainage precautions should be
observed during construction and maintained at all times after the residence 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 (if any)
should be covered with filter fabric and capped with about 2 feet of the on-site
soils to reduce surface water infiltration. Graded swales should have a minimum
slope of 3%.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Kumar & Associates, lnc. @ Project No.21-7-434
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Landscaping which requires regular heavy irrigation should be located at least
10 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 irrigation.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this area at this time. V/e 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 1, 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 concemed a6out 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.
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 verifu that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recommendations presented herein. Vy'e 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, Inc.
W T. P*tr¿na.¿
James H. Parsons, P.E
Reviewed by:
Steven L. Pawlak, P.E.
JHP/kac
s)
Kumar & Associates, lnc. @ Project No. 21.7-434
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98.0'
78.0'/oo
LOT 37
69.4'
SETBACK
r25.1'
BORING 2
o
PROPERTY
LI\IE
O soRrNc t
\
140
78.0
LOT 38
126 .9'
I PROI
LINJ
2L .6'
5
tl¡.
drïf*Øð
1 0 15 30
APPROXIMATE SCALE_FEET
21 -7 -434 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
WC= I .6
*4=53
-200=8
BORING 1
EL. 111'
BORING
EL. 110
2
0 022/ 12
WC=5.9
DD= 1 05
-2OO=45
26/12
tNC=7.7
DD=1 1 0
-200=72
5
28/ 12 t15/ 12
WC=7.6
DD= 1 02
70/12 45/6,50/5F-
LiJ
L¡J
LL
I-l-
o_
t¡Jo
10
71 /12 50/5 10
f-
t¡Jt!
LL
I-t-(L
t¡lo
15 1530/6,50/1
20 20
Fig. 221 -7 -434 Kumar & Associates LOGS OF EXPLORATORY BORINGS
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LEG END
FILL: CLAY, SANDY TO VERY SANDY, SILTY, SCATTERED GRAVEL, VERY STIFF, SLIGHTLY
MOIST, MIXED BROWN.
CLAY (CL); SANDY, STIFF, SLIGHTLY MOIST, TAN T0 LIGHT BROWN
GRAVEL (CV-Cp); VERY SANDY, COBBLES, PROBABLE BOULDERS, SLIGHTLY SILTY, DENSE,
SLIGHTLY MOIST, MIXED BROWN. ROUNDED ROCK.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE
i DRTVE SAMPLE, 1 3/8-INCH LD. SPLIT SPOON STANDARD PENETRATION TEST.
^^ 1A^ DRIVE SAMPLE BLOW COUNT' INDICATES THAT 22 BLOWS OF A 14o-POUND HAMMERzz/ t ¿ FALLTNG 30 TNcHES wERE REQUIRED To DRtvE THE sAMPLER 12 tNcHES.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON MAY 18 AND JUNE 14, 2021 WITH A 4-INCH
DIAMETER CONTINUOUS-FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED AND ASSUMED ELEVATIONS SHOWN ON FIGURE 1 .
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 WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);
DD = DRY DENSITY (PCt) (NSTV D2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913);
_ZQO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D1140).
Fig. 3Kumar & Associates LEGEND AND NOTES21 -7 -434
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SAMPLE OF: Sondy Silty Cloy
FROM:Boring2@5'
WC = 7.6 %, DD = 102 pcf
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'fhe
¡n
opprovol
Sw€ll
ln
'r - - i-'-'l
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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àq
JJ
L¡J
=(n
I
zotr
ô
=o
t/1z.oo
0
-1
2
5
4
1.0 APPLIED PRESSURE -100
Fig. 4Kumar & Associates SWELL-CONSOLIDATION TTST RESULTS21 -7 -434
too
90
ao
70
60
50
40
30
20
10
o
HYDROMETER ANALYSIS SIEVE ANALYSIS
fIMË RÉÀDINGS
6ôUtN teltN ¡Mtñ2,+ HRS 7 HRS
'
MIN t,
U.S. STANDARD SERIËS
I
CLEAR SQUARE OPENINGS
t/^, a/^n 1 1/r'0
10
20
30
,io
50
60
70
80
90
loo
=E
.o0l .002 .oo5 .125 2-O 152
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT COBBLES
GRAVEL 53 % SAND 59
LIQUID LIMIT
SAMPLE OF: Slightly Sllty Sond ond Grovel
PLASTICITY INDEX
SILT AND CLAY 8 %
FROM:BoringlOT'&10'
Thoso lo lhs
lho
sholl nol b€
wllhoul tho
rsproduc€d,
wrlllen
ls
I5, ASTM
ASTM Cl36 ond/or ASTM D1140.
SAND GRAVEL
FINE MEDIUM COARSE FINE COARSE
Kumar & Associates GRADATION TEST RESULTS Fis.521 -1 -434
l*rt*içl['ffifËtr*'"'Ë;;**'
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.21-7-434
Sandy Silty Clay (Fill)
Sandy Silty Clay
SOIL TYPE
Silty Sand and Clay (Fill)
Slightly Silty Sandy Gravel
(psfl
UNCONFINED
COMPRESSIVE
STRENGTH
("/"1
PLASTIC
INDEX
ATTERBERG LIMITS
(%l
LIQUID LIMIT
PERCENT
PASSING NO.
200 stEVE
45
8
72
SAND
("/ù
3953
GRADATION
t:/"1
GRAVEL
locfl
NATURAL
DRY
DENSITY
105
110
t02
7.7
7.6
lo/"1
NATURAL
MOISTURE
CONTENT
5.9
61
2%
5
tft)
DEPTH
1
7 and 10
Combined
BORING
1
2