HomeMy WebLinkAboutSubsoil Studytcrt lfumar & Associates, 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), Parke¡ Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 56, PHASE 3,IRONBRIDGE
BLUE HERON DRIVE
GARFIELD COUNTY, COLORADO
PROJECT NO. 21-7-438
JULY 9,2021
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 ST'UDY
PROPOSED CONSTRUCTION
SITE CONDITIONS
SUBSIDENCE POTENTIAL..
FIELD EXPLORATION
SUBSURFACE CONDITIONS
FOLINDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS
FOUNDATIONS
FLOOR SLABS.....
UNDERDRAIN 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
-1
1
1
a
1...- L -
-3 -
-3 -
..-3 -
..-3 -
..-4-
..-5-
..-5-
-6-
Kumar & Associates, lnc, @ Project No. 2l-7'438
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot 56, Phase 3, Ironbridge, Blue Heron Drive, 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 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 held 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
Development plans for the lot were preliminary at the time of our study. In general, the
proposed residence will be a one- and two-story wood-frame structure with attached gara5e.
Ground floors are expected to be a combination of structural over crawlspace and 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 vacant at the time of our field exploration. The ground surface is gently
sloping down to the north in the building area. A steep cut slope from previous subdivision
development is located south of the building area sloping down to the north at a grade of around
30 percent. Vegetation consists of grass and weeds.
Kumar & Associates, lnc. o Project No, 2l-7.438
.,
STTBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite unclerlies the Ironbriclge development.
These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some
rnassive becls of gypsum and limestone. There is a possibility that massive gypsum deposits
associated with the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the
gypsum under certain conditions can cause 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 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 were 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 56 throughout the service life of the proposed residence, in our
opinion, is low and similar to other lots in the area of similar subsurface profiles; 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 flreld exploration for the project was conducted on June 15, 202L 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 1%-inch and 2-inch I.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.
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 Rorings, Figure 2. The samples were returned to our
laboratory for review by the project engineer and testing.
Kumar & Associates, lnc. o Project No, 21"7-438
a-J-
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about l% feet of stiff to very stiff, sandy silty clay overlying dense, slightly
silty sandy gravel and cobbles with 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 possible boulders and drilling refusal was encountered in Boring I at 13 feet deep.
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
relatively undisturbed drive samples of the clay soils, presented on Figure 4, indicate low to
moderate compressibility under existing low conditions and light loading and a minor expansion
potential when wetted. Results of gradation analyses performed on small diameter drive samples
(minus lYz-inch fraction) of the coarse granular subsoils are shown on Figure 5. The laboratory
testing is summarizedin Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
FOUNDATION BEARING CONDITIONS
The upper clay soils encountered in the borings possess low bearing capacity and typically a low
to moderate settlement potential if wetted. Our experience in the area indicates the swell
potential is minor (if any) and can be discounted in foundation design. Vy'e should observe the
soil conditions exposed at the time of excavation and evaluate them for swell-compression
potential and possible mitigation. Shallow spread footings placed on the clay soils can be used
for support of the proposed residence with a risk of foundation movement if the bearing soils
become wetted. Proper surface drainage as described in this report will be critical to the long-
term performance of the structure.
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 soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
Kumar & Associates, lnc. o Project No. 21-7-438
-4-
r)Footirrgs placed ott tltc uldisturbed natrral soils shoulcl be clesigned for an
allowable l-learing pressrlre of 1,500 psf. Based on experience, we expeut initial
settlement of tttotings designed and constructed as discussed in this section will
be about 1 inch or less. Additional post-construction movement of around I inch
could occur if the bearing soils become wetted.
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 founclations at least 36 inches below exterior grade is typically used in this
atea.
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 a
lateral earth pressure coffesponding to an equivalent fluid unit weight of at least
55 pcf for the onsite soils as backfill.
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.
A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
2)
3)
4)
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 such as road base should be placed beneath interior slabs for
support. This material should consist of minus 2-inch aggregate with at least 50% retained on
the No. 4 sieve and less than 12o/o passing the No. 200 sieve.
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 soils devoid of vegetation, topsoil ancl oversized rock or a suitable imported granular
material such as road base.
s)
6)
Kumar & Associates, lnc, @ Project No. 21-7.438
5
UNDERDRAIN SYSTEM
It is our understanding the ground finished floor elevation of the residence is at or above the
surrounding grade. Therefore, a foundation drain system is not recommended. It has been our
experience in the arcathat 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 and basement
areas, if provided, be protected from wetting and hydrostatic pressure buildup by an underdrain
and wall drain system. An underdrain is not recommended around the crawlspaçe area to help
limit the potential for wetting below the shallow footings.
If the finished floor elevation of the proposed structure has 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
It will be critical for the long-term performance of the building foundation that the bearing soils
be protected from wetting. The following drainage precautions should be observed during
construction and maintained at all times after the residence has been completed:
1) Inundation ofthe foundation excavations and underslab areas should be avoided
during construction. Excessive drying could increase the expansion potential of
the exposed soils.
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. Graded swales should have a
minimum slope of 3%
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
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.
Kumar & Associates, lnc. o Project No.2l-7.438
-6-
LIMIT'A 'IONS
This study has heen conducfed in accordance with gonorally accopted gootoclrnical engineering
principles antl practices in this area at this timc. 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 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 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 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 veriff 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, fnc.
James H. Parsons, P.
Reviewed by:
Steven L. Pawlak, P.E.
JHPlkac
Kumar & Associates, lnc.ù Project No. 21.7.438
.lr
r¡¡
?l
gg
PROPERTY
LINE
BORING 1
LOT 56
102.0'
SETBACK
0'
2o\
1,,0'
'1 9
'7 9 .0'
PROPERTY
LTNE
LOT 55
102
80. (
PR.OPERTY
L]NE
LOT 51
L02
SETBACK
1
APPROXIMATE SCALE-FEET
21 -7 -438 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
I
BORING 1
EL. I 00'
BORING 2
EL. 1 00'
0 ô
13/ 12
WC=4.3
DD= 1 05
15/ 12
WC=6.8
DD=98
-200=80
41/12
15/ 12
15/ 12
WC=6.6
DD=97
q
F-
L¡J
UJ
LL
I-t-(L
t¡lo
53/ 12 t-
t¡J
t¡JtL
I
:El-fL
L¡lo
10 1045/ 12 28/6, 50/2
15 1563/12
20 20
WC=0.4
+4=55
-200= 1 0
21 -7 - 438 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
I
E
I
I
:
è
I
LEGEND
cLAY (cL); SILTY, SANDY, STIFF TO VERY STIFF, SLIGHTLY MOIST, LIGHT BROWN, LOW
PLASTICITY, SLIGHTLY POROUS.
GRAVEL (GM-GP); SLIGHTLY SILTY, VERY SANDY, COBBLES, POSSIBLE BOULDERS,
SLIGHTLY MOIST, MIXED BROWN AND GRAY.
DENSE,
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
I DRTVE SAMPLE, 1 3/8-INCH l.D. SPLIT SPOON STANDARD PENETRATION TEST
13/ 12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 15 BLOWS OF A 14o_POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
I PRACTICAL AUGER REFUSAL.
NOTES
1 . THE EXPLORATORY BORINGS WERE DRILLED ON JUNE 1 5, 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.
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 RESULÏS:
WC = WATER CONTENT (%) (ASTM D2216);
DD = DRY DENSITY (pcf) (lsrv D2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913);
_2QO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM 01140).
21-7 -438 Kumar & Associates LEGEND AND NOTES Fig.3
I
I
F{
1r
SAMPLE OF: Sondy Silty Cloy
FROM:Boringl@2.5'
WC = 4.5 %, DD = 103 pcf
às
JJ
l¿J
=U''
I
z.9t-
Õ
=o
U)z.oll
1
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
0
-1
-2
-3
-4
1.0 PRESSURE _ KSF 10
JJ
t¡J
=U)
I
zotr
ô
J()
Øzoo
1
0
-1
-2
-5
1.0 APPLIED PRESSURE -100
SAMPLE 0F: Sondy Silty Cloy
FROM:Boring2@5'
WC = 6.6 %, DD = 97 pcf
¡n
tho
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
21 -7 -438 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
ñ
/;
P
I
E{
1r
r&
ei
d.9
:i
100
90
a0
70
60
50
40
50
20
lo
o
o
10
20
30
10
50
60
E
¡
I l70
-80
90
foo
.019 .o57 3ô.t 76.2
-125 2.O
DIAMETER OF PARTICLES IN MILLIMET
CLAY TO SILT COBBLES
GRAVEL 53 % SAND
LIQUID TIMIT
SAMPLE OF: Slightly Silty Sondy Grovel
37%
PLASTICITY INDEX
SILT AND CLAY 10 %
FROM: Boring 2 @ 1O' &15' (Combined)
Th6so lo3l r€sulls opply only lo lhe
somples whlch wero losl6d. Th€
Ìosllng roporl sholl nol bo r€produc€d,
oxcopl ln full, w¡lhoul lhe wrlllon
opprovol of Kumor & Associolcs, lnc.
Sleva qnolys¡s l63llng ls portormod ln
occordqnca wllh ASTM D6915, ASTM 07928,
ASTM Cl56 ond/or ASTM 01140.
HYDROMETER ANALYSIS SIEVE ANALYSIS
U,S. STÀNDARO SÊRIES
5"6' I
CLEAR SQUARE OPENINGS
\/^" \//n I I/tâ
TIYE READINôS
2,4 HRS 7 HRS i utN¡vtN 4t
ti
SAND GRAVEL
MEDIUM COARSE FINE COARSEFINE
21 -7 -438 Kumar & Associates GRADATION TEST RESULTS Fig.5
lGrt *ffil[#ffËtr*iii;'*"TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.21-7-438Sandy Silty ClaySandy Siltl ClaySandy Silty ClaySOILTYPESlightl]' Siþ Sandy Gravel{osflUNCONFINEDCOMPRESSIVESTRENGTH("/rlPLASTICINDEXATTERBERG LIMITS(%lLIQUID LIMITPERCENTPASSING NO.200 stEvE80015t53GRADATIONNATURALDRYDENSTTYNATURALMOISTURECONÏENTSANDP/,1GRAVELtf/"|10398976.60.46.8tfttDEPTH4.32/,5510 and 15combinedSAMPLE LOCATIONBORING12