HomeMy WebLinkAboutSubsoil Studyr(trt l(umar&Associatesnlnc. 5020 County Road 154
Geotechnical and Materials Engineers Glenwood Springs, CO 81601
and Environmentalscientists phone: (g7o) g4s-7ggg
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
An Employco Owncd compony www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOT]NDATION DESIGN
PROPOSED RESIDENCE
LOT ZL,IRONBRIDGE, PHASE III
RIVER BEND \ilAY
GARFIELD COUNTY, COLORADO
PROJECT NO.2l-7-547
AUGUST 2,2021
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 CONSTRI ]CTION
SITE CONDITIONS....
SUBSIDENCE POTENTIAL......
FIELD EXPLORATION
SI IBSTIRFACE CONDITIONS ...
FOUNDA'I'ION tsEARING CONDITIONS
DESIGN RECOMMENDATIONS
FOUNDATIONS
FLOOR SLABS
UNDERDRAIN 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 - SI]MMARY OF I,ABORATORY TEST RESULTS
-1
I
1
1
.-2-
.,
-L-
..........- 3 -
..- 3
..- 3
',- 4
..- 4
..- 5
-6-
Kumar & Associates, lnc.Project No.21-7.547
PURPOSE AND SCOPE OF STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on
Lot22,Ironbridge, Phase III, River Bend V/ay, Garfield County, 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 SCIB, LLC dated June 28, 202I.
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
Design plans for the proposed residence were preliminary at the time of our study. In general,
we assume the residence will be located between the exploratory borings shown on Figure 1 and
be a one or two-story wood-frame structure over crawlspace with a slab-on-grade floor in the
garage. Grading for the structure is assumed to be relatively minor with cut depths between
about 3 to 5 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 lot was vacant and sloped gently down to the north-northwest toward the Roaring Fork
River with about 2 to 3 feet of elevation difference in the general building area. Vegetation
consisted of grass, weeds and scattered brush.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Ironbridge development.
These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some
Kumar & Associates, lnc,Project No. 21-7-547
-2-
massive bcds of gypsum and limestone. There is a possibility that rnassive gypsum deposits
associated with the Eagle Valley Evaporite unclerlie portions of the lot. Dissolution of the
gypsum under certain conditions can causc sinkholes to develop and can produce areas of
localized subsidence. During previous work in the area, several sinkholes were observed
scattered throughout the Ironbridge development. These sinkholes appear similar to others
associated with the Eagle Valley Evaporite in areas of the lower Roaring Fork River valley.
Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities
was encountered in the subsurface materials; however, the exploratory borings wcre relatively
shallow, for foundation design only. Based on our present knowledge of the subsurface
conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of
future ground subsidence on Lot 22 throughout the service life of the proposed residence, in our
opinion, is low and similar to ol.lter loLs in the area; 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 tlesired, we should be contacted.
FIDLD EXPLORATION
The field exploration for the project was conducted on July 14, 202I. Two exploratory borings
were drilled at the locations shown on Figure I 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 I% inch and 2-inch LD. spoon samplers. The samplers
were driven into the subsoils at various depths with blows tiom a 140 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, 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. Below
a thin topsoil layer, the subsoils consist of dense, slightly siþ sandy gravel and cobbles and
probable small boulders in Boring I and about 8% feet of stiff sandy silty clay and medium
dense/stiff silty sand and sandy silt in Boring 2 above dense, slightly silty sandy gravel and
cobbles dowr to the explored clepl.hs of about 7 to 16 feet. Drilling in the dense, coarse granular
Kumar & Associates, lnc.Project No.21.7.547
-3 -
soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was
encountered in the deposit in Boring 1.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and gradation analyses. Results of swell-consolidation testing performed on
a relatively undisturbed drive sample of the clay soil, presented on Figure 4, indicate low
compressibility under light loading and low expansion potential when wetted. Results of
gradation analyses performed on small diameter drive samples of the coarse granular subsoils
(minus lYz-inch fraction) are shown on Figure 5. The laboratory testing is summarized in
T'able l.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
FOUNDATION BEARING CONDITIONS
The clay, silt and sand soils encountered at Boring 2 onfhe lot have variable movement potential
mainly when wetted under lightly loaded, shallow spread footings. Footings can be used for
support of the building and should be deepened below the upper fine-grained soils and placed on
the underlying dense, sandy gravel and cobble soil to achieve a low movement risk. We should
evaluate the exposed bearing conditions at the time of construction for movement potential and
the need to lower the bearing elevation. Design bearing level of sub-excavated areas can be
reestablished with compacted structural fill.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, the building can be founded with spread footings bearing on the
natural gravel and cobble soils with a low settlement risk. Structural fill used to reestablish
design bearing level should consist of granular material compacted to at least 98% of standard
Proctor density atnear optimum moisture content and extend laterally beyond the footing edges a
distance equal to at least one-half the depth of frll below the footing.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural gravel and cobble soil or compacted
structural fill should be designed for an allowable bearing pressure of 2,500 psf.
Based on experience, we expect settlement of footings designed and constructed
as discussed in this section will be about %to I inch or less.
Kumar & Associates, lnc,Project No.21-7-547
-4-
3)
The footings should have a minimum width of 16 inches for continuous walls and
2 feet for isolatecl 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
aÍea.
Continuous foundation walls should be reinfbrced 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 coiresponding to an equivalent fluid unit weight of at least
55 pcf for the onsite sandy silty clay soil or 45 pcf for the onsite or imported
sandy gravel soil as backfill.
The topsoil, clay, silt and sand soils and loose or disturbed soils should be
removed in footing areas down to the dense sandy gravel and cobble soil. The
exposed soils in footing arcas should then be moistened and compacted.
Stmctural fill placed in footing areas should extend laterally beyond the footing
edge a distance equal to at least one-half the depth of fill below the footing.
A representative ofthe geotechnical engineer should observe all footing
excavations prior to concrete placement to evah¡ate bearing conclitions.
4)
s)
FLOOR SLABS
The natural granular soils are suitable to support lightly loaded slab-on-grade construction. Slabs
underlain by clay soils will have a risk of movement due to expansion potential and structural fill
at least 2 feet deep should be placcd bclow the slab in clay areas to lirnit the movernent risk. Tg
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 thc inl.endetl slab use.
All fill materials tbr support of floor slabs should be compacted to at least 95o/o of maximum
standard Proctor density at a moisture content near optimum. Requirecl fill can consist of the
on-site gravel soils devoid ofoversized rock, vegetation, and topsoil.
TINDERDRAIN SYS'I'EM
Although free water was not encountered during our exploration, it has been our experience in
the area that local perched groundwater can develop during times of heavy precipitation or
2)
6)
Kumar & Associates, lnc.Project No.21.7-547
-5-
seasonal runoff. Frozen ground during spring runoff can also create a perched condition. We
recommend below-grade construction, such as retaining walls and basement areas (if any), be
protected from wetting and hydrostatic pressure buildup by an underdrain system. Shallow
crawlspace (about 4 feethigh) should not need a perimeter underdrain with proper backfill
placement and surface grading.
If required, 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 with the drain invert elevation at least 1 foot below lowest
adjacent finish grade and sloped at a minimum t7o to a suitable gravity outlet or drywell based in
the sandy gravel and cobble soil. Free-draining grarnlar 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 lYz feet deep.
SURFACE DRAINAGE
Providing proper surface grading and drainage is very important to the 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 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. Free-draining wall backfill should be
covered with filter fabric and capped with about 2 feet of the on-site finer grained
soils to reduce surface water infiltration'
4) Roof downspouts and drains should discharge well beyond the limits of all
backhll.
5) 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 inigation
Kumar & Associates, lnc.Project No.21-7-547
-6-
LIMITATIONS
This stucly has been conducted in accordance with generally acccptcd gcotcchnical engineering
principles and practices in this arca at this time. We make no war:ranty 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 arca. Our services do not include detennining the
presence, prevention or possibility of mold or other biological contaminants (MOBC) developing
in the future. 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 appear different from those described in this report, we should be notifiecl 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 projcct evolves, we
should provide continued consultation and field services during construction to review and
monitor the implementation of our recommenclations, and to verify 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, Inc.
Steven L. Pawlak,
Reviewed by:
Daniel E. Hardin, P.E.
SLPlkac
Kumar & Associates, lnc
I
Project No, 21.7.547
23C .6
LOT 21 80.9,
230. B'
2
159.1 '
109.2'SlÌTBhCK
LOT 22
228. r
705 .2
1.44.i
NGl /;,
3/199..t'LOT 2
BENCHMARK:
SEIVER MANHOLE RIM
EL. 100,, ASSUMED
*.- i45,!,60. c
\\-_1F5.1
2002040
APPROXIMATE SCALE-FEET
21 -7 -547 Kumar & Associates LOCATION OF TXPLORATORY BORINGS 1Fig.
I
I
€
I
WC=0.6
+4=67
-2Q0=7
BORING 1
EL. g4'BORING 2
EL. 91 .7'
U 0
38/12
13/ 12
WC=9.1
DD=110
5 10/ 12
WC=4.8
DD= 1 00
-200=58
550/5.s
F
L¡l
L¡J
LL
I-F
o_
t¡Jo
10/12 F
UJ
t¡J
LL
I-t-fL
Lrlô
10 10
68/ 12
15 1543/ 12
20 20
21-7 -547 Kumar & Associates LOGS OF TXPLORATORY BORINGS Fig. 2
I
LEGEND
TOPSOIL; ORGANIC SANDY SILT AND CLAY, SLIGHTLY MOIST, BROWN
CLAY (CL); SILTY, SANDY, STIFF, SLIGHTLY MOIST, LIGHT BROWN, LOW PLASTICITY
SAND AND SILT (SM-ML); FINE SAND, MEDIUM DENSE/STIFF, SLIGHTLY MOIST, LIGHT
BROWN.
GRAVEL AND COBBLES (GM-GP); SLIGHTLY SILTY To SILTY, SANDY, PROBABLE BoULDERS,
DENSE, SLIGHTLY MOIST, GRAY BROWN, ROUNDED ROCK.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE
i DRTVE SAMPLE, 1 3/8-INCH l.D. SPLIT SPOON STANDARD PENETRATION TEST
7e/,11 DRTVE SAMPLE BLOW CoUNT. |ND|CATES THAT 38 BLoWS OF A 140-P0UND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
I PRACTICAL AUGER REFUSAL.
NOTES
1 . THE EXPLORATORY BORINGS WERE DRILLED ON JULY 1 4, 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 MEASURED BY INSTRUMENT LEVEL AND
REFER TO THE BENCI{MARK ON FIG. 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 (¡STV OOSIg);
-2QO= PERCENTAGE PASSING No. 200 SIEVE (ASTM 01140).
21 -7 -547 Kumar & Associates LTGEND AND NOTES Fig.3
I
I
Ê
f
I
j
I
i
l
lil
irll
iiilì
l
l,tl
l
I
i
2
0
-1
-2
_z
I'
i
r
l
l
I
l
i
I
i
I
I
APPLIED PRESSURE . KSF
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
I
i
:
I
I
,
l
+
I
I
I
I
l
I
.
)
I
I
I
I
l
l
)
I
i
i
!
JJl¡l
=ar1
I
zotr
o
Jo
v1z.o
C)
i'I
j i
I
.0 10 t00
SAMPLE OF: Sondy Clcy
FROM:Boring2e^2.5'
WC = 9.1 %, DD = 110 pcf
Bomp16€
ãholl not
full, without th€
Consolldotion
21-7 -547 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fí9. 4
F
ð
ñ
SIEVE ÂNÂLYSISHYDROMETER ANALYSIS
CLEAR SAUARE OPENINGS
a/e-a/t-1./t,
TIME REÂDINGS
24 HRS 7 HRS MN 41 00
U.S. STANOÂRD SERIES
¡50 4¿O {30 {16 {10 4A
I
l I I
I
I
I
I
I
L
I
too
90
80
70
60
50
10
30
20
l0
o
o
10
20
30
40
60
70
ao
90
too
=f
.o37 ,075 200
152
DIAMETER OF IN MILLI
CLAY TO SILT COBBLES
GRAVEL 67 % SAND 26
LIQUID LIMIT
SAMPLE OF: Slightly Silty Sondy Grovel
PLASTICITY INDEX
SILT AND CLAY 7 %
FROM: Boring 1 @ 2.5' & 5' (Combined)
Thos€ lesl rosulls opply only lo lh6
sompl€s whích wsrs l€sl6d. Thg
losllng r€porl sholl nol be roproduc€d,
€xc€pl ln full, wllhout lh€ wrlllon
opprovol of Kumor & Associol€s, lnc.
Slevg onolysls losllng ¡s performod in
occordoncs wlth ASIM 06915, ASTM D7928,
ASTM Cl56 ond,/or ASTM 011,10.
GRAVELSAND
COARSE FIN E COARSEFI NE MEDIUM
21 -7 -547 Kumar & Associates GRADATION TEST RTSULTS Fig.5
l*rtiiË*fi'ffiffffi1'lÊ'i'n""TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.21-7-5ttrSOIL TYPESlightly Silty Sandy GravelSandy ClayVery Sandy SiltUNCONFINEDCOMPRESSIVESTRENGTHLIQUID LIMITLIMITSPLASTICINDEX72667PERCENTPASSING NO.200 srEvE58("/rlSANDGRADATION(:/"1GRAVELBORINGLOCATIONDEPTHNATURALDRYDENSITYNAIURALMOISTURECONTENT1101000.6I94.82% and5combined2%5I2