HomeMy WebLinkAboutSubsoils Report for Foundation DesignI(t'T ltumar & Associates, lnc. 5020 County Road 154
Geotechnical and Materials Engineers Glenwood Springs, CO 81601
and Env¡ronmentatscientists phonè: (g7o) 945_7gsg
fax: (970)945-8454
email : kaglenwood@kumarusa.com
An Employcc Owncd Compony 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
LOT 60, TRONBRTDGE, PHASE 3
TBD BLUE HERON DRIVE
GARFTELD COUNTY, COLORADO
PROJECT NO. 21-7-683
ocroBERt2,202t
PREPARED FOR:
SCIB, LLC
ATTN: LUKE GOSDA
0115 BOOMERANG ROAD, SUITE 52018
ASPEN, COLORADO 81611
luke. gosda@sunriseco.com
TABLE OF CONTENTS
PURPOSE AND SCOPD OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS.
SUBSIDENCE POTENTIAL...
FIELD EXPLORATION .
SUBSURFACE CONDITIONS
FOI INDATTON BEARING CONDITIONS
DESIGN RECOMMENDATIONS
FOUNDATIONS.
FLOOR SLABS
IINDERDRATN 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
1
1
..-2-
..-2-
........- 3 -
..-3-
4
4
5
5
6
..-6-
..- I -
Kumar & Associates, lnc.Project No. 21-7-683
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot 60, Ironbridge, Phase 3, TBD Blue Heron Drive in 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 August 2,202I.
A field exploration program consisting of two 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 potential, 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
At the time of our study, design plans for the residence had not been developed. The building is
proposed within the building envelope shown on Figure 1. For the purposes of our analysis, we
assume the proposed residence will be a one- or two- story wood-frame structure over a
crawlspace with an attached slab-on-grade garage. 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 notif,red to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The lot was vacant and appeared to have had minor cut and fill grading, likely during the
subdivision development. The surface of the lot slopes mostly gently down to the northeast with
about 7 feet of elevation difference across the building envelope area. An asphalt paved path
follows the west side of the lot. Vegetation consists of sparse grasses and weeds.
Kumar & Associates, lnc,Project No, 21-7-683
a
SUBSIDENCE POTENTIAL
The geologic conditions were described in a previous report conducted for planning and
preliminary clesign of the overall subclivision clevelopment by Hepworth-Pawlak Geotechnical
(now Kumar & Associates) dated October 29,1997, Job No. I97 327. The natural soils on the
lot mainly consist of sandy clay and silt 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 2 to 3 t'eet 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 60 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 irnmediate 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 60 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 September 1,202I. Two exploratory
borings were drilled at the approximate 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-mountcd CME-458 drill rig. The borings were logged by a representative of I(umar
& Associates, Inc.
Samples of the subsoils were taken with l7å-inch and Z-inch I.D. California or split-spoon
samplers. The samplers were driven into the subsoils at various depths with blows from a 140-
pound hammer talhng 30 rnches. 'l'his test is similar to the standard penetration test described by
AS'IM Method D-1586. The penetration resistance values are an indication of the relative
Kumar & Associates, lnc.Project No. 21-7-683
-3 -
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
about 6 inches of topsoil, the subsoils consist of about I to 5 feet of stiff, slightly sandyto sandy
clay and silt overlying medium dense to very dense, slightly silty to silty, sandy gravel and
cobbles with possible boulders down to the maximum explored depths of 7 and 12%feet.
Drilling in the coarse granular materials with auger equipment was difficult due to the cobbles
and probable boulders and practical drilling refusal was encountered in the deposit.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density, swell-consolidation and percent silt and clay-sized particles passing the No.
200 sieve, and gradation analysis. Results of swell-consolidation testing performed on a
relatively undisturbed drive sample of clay and silt soils, presented on Figure 4, indicate low
compressibility under existing low moisture conditions and light loading and minor expansion
potential when wetted under loading. The results of a gradation analysis performed on combined
samples of slightly silty, sandy gravel (minus IYz-inch fraction) obtained from the site are
presented 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.
FOUNDATION BEARING CONDITIONS
The upper clay and silt soils encountered in the borings possess low bearing capacity and
typically a low to moderate settlement potential if wetted. Testing indicates the clay and silt is
slightly expansive. Our experience in the area indicates the swell potential is minor (if any) and
can be discounted in foundation design. We should observe the soil conditions exposed at the
time of excavation and evaluate them for swell-compression potential and possible mitigation
such as sub-excavation to a certain depth and replacement with compacted structural fill or
extending the foundation bearing level down to the underlying dense granular soils. Shallow
spread footings placed on the claylsilt and sandy gravel soils can be used for support ofthe
proposed residence with a risk of foundation movement mainly if the fine-grained bearing soils
become wetted. If foundations bear on both the sandy gravel and clay and silt soils, there will be
Kumar & Associates, lnc.Project No. 2l-7-683
-4-
a risk of potential post-construction differential movement. If a lower risk of clifferential
movement is desired, foundation bearing levels should be extended down and bear entirely on
the untlerlying, relatively dense coarse granular soils. Proper surface drainage as described in
this report will be critical to the long-term perfonnance 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 1) spread footings bearing on both
the natural claylsilt and sandy gravel soils with a differential settlement risk or, 2) spread
footings bearing on the underlying natural, dense granular soils with a low risk of settlement.
'['he desìgn and constnrction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils should be designed for an
allowable bearing pressure of 1,500 Footings placed on the undisturbed
2)
natural granular soils should be designed for an allowable bearing pressure of
3,000 psf. Based on experience, we expect initial settlement of footings designed
k
and constructed as discussed in this section will be about 1 inch or less.
Additional differential ntovement up to about I inch could occur if the clay and
silt bearing soils are 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 foundations at leastS6 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 12 feef .
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
50 pcf for Lhe on-site soil as backfill, excluding organics and rock larger than
6 inches.
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
3)
4)
s)
Kumar & Associates, lnc.Project No.21.7.683
5
should then be moistened and compacted. Structural fill should consist of
relatively well-graded onsite granular material or imported road base compacted
to at least 98Yo of standard Proctor density atnear optimum moisture content.
The fill should extend beyond the footing edges a distance at least equal to one-
half the fill depth below the footing.
6) A renresentative of the seotechnical enqineer should observe all footins
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 with a risk of movement mainly if the fine-grained bearing soils are wetted. 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 l2Yo 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 and oversized rock or a suitable imported material such as
road base.
UNDERDRAIN SYSTEM
It is our understanding the ground level, 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 area and where clay soils are present 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 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 garage and shallow crawlspace areato help limit the potential for wetting below the
shallow footings.
Kumar & Associates, lnc.Project No. 21-7-683
-6-
If the f,rnishecl floor elevation of the proposed stnrcture has a floor level below the surronncling
gracle or a taller crawlspace is constmctecl, we should be contacfecl to provicle recommenclations
for an underdrain system. All earth retaining structures shoulcl be properly drained.
SURFACE DRAINAGE
Tt rvill be critical to the builcling performance to keep the bearing soils clry. The follolving
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.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95Yo of the maximum standard Proctor density in pavement and slab areas
and to at least 90% 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 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 af this time. 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 l, the proposed type of
^^-^+-,^+:^- ^-l ^.,- ^.,^^-:^'^^^:.^ +L^ ^-^^ ^,.- ^^-.,:^^^ l^ .^^+:^^1,,.J^ l^+^*i'^i.^^ +L^\,urrsLlur/Lrurr arlu rrut rJ^pçrlçtllyç ltl LIIç dtvd. \_,rur ¡çl vlvlù Llu rtut ilrvluuç \tr-turltlltlllré tltç
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 f,reld of
practice should he consulled. Our findings inchrde interpolation and exfrapolation of the
subsurface conditions identified at the exploratory borings and variations in the subsurface
Kumar & Associates, lnc.Project No. 21-7-683
-7 -
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 recortmendations 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 reconìmendations, and to veriff that the recornmendations
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.
Ì',.-^-u &,
I¿N-,'
Mark Gayeski, E.I.T.
Reviewed by:
Steven L. Paw
SLP/kac
5222Ia
ôI
Kumar & Associates, lnc.Project No, 21-7.683
d
2" ø PVC RISER/
tst
MARKER)
gÊNCHURK o
BORING 1
=598.93'-/./
\
_I-
ô!ùfo -
-/
5q¡
'-l
I
-1-
t\I \-l-rcsl {¡ppenett
¡ uruw mRKER)
\l\ttlrl\l
''l
t\t'.l\,
lrt\t\
I t.
t\
l1t\t\
I t.
t\
I
I'l
I
.try,
5*s
LOT 60
TBD BLUE HERON DRIVE
'14,3()6 So.Fr.
o.33 ACRE *
. PARCELNo.
"ø zggsotgsooco\\
--_
1O.O'ffiEMÊNI FOR
UIIIIT¡ES AND OMINAGE
(REC No 8ææ9)
1O.O'EASEMENT FOR
DMINAGE
{RECNo868309) -.596r.
OBORING
2
tt'
"rA
sú-
q UTITIIIESAND DMINAGÊ
(RFc N¡ t68309)
ç$
. {APPÆEMfrtLtw
RISER (o
^ôı28Fd9^u^:#H
N11
BASIS OF
CORNER
sEcloN 1,7S. R89W,
2r'rRoN P|PE
wßlM BMSS CAP
o
to.i Õ
':(f)do
iHfLooN
SE olo
FalJ
GLO rol 27,
sEcTtoN 1, T7S, R89W
2r" rRoN P|PE
ø3'ALLOYCÀPGARCO 1967
T-POST-
urrltw I
u¡nxenl \t
96.1 COMMONPUBLIC SERVICE COMPANY
ELECIRIC EASEMÊNT
AREA
PARCEL No.
?30601330102
10 0 i0 20
APPROXIMATE SCALE-FEET
"'"r"'l NO.207167
21 -7 -683 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig 1
WC=0.5
+4=57
-200=1 1
BORING 1
EL. 5946.5'
BORING 2
EL. 5952'
U 0
24/6, 50/3
12/ 12
WC=8.0
-2OO=97
COMBIN ED
5 6/6, sO/4
WC=6.2
DD= 1 00
-200= 68
5
F
L¡J
L¡Jl!
I-Fo-
t¡.jÕ
51 /6 F
l¡J
LJtL
I-FfL
l¿Jo
10 28/ 12
10
15 't5
21 -7 -683 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
I
I
E
!?
I
E
I
9
LEGEND
N
TOPSOIL; CLAY AND SILT, SANDY, GRAVELLY, ORGANICS, FIRM, SLIGHTLY MOIST, DARK
BROWN.
CLAY AND SILT
CALCAREOUSNE
(cl--vl-); sANDy, slFF, sLtcHTLy Motsr, BRowN, SLtGHTLv poRous, TRAcE
SS.
GRAVEL AND COBBLES (GM); SANDY, SLIGHTLY SILTY TO SILTY WITH PROBABLE SMALL
BOULDERS, MEDIUM DENSE TO VERY DENSE, SLIGHTLY MOIST, MIXED BROWN.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
i DRrVE SAMpLE, 1 5/8-tNCH t.D. SpLtT SpooN STANDARD pENETRATTON TEST.
50/3 DRIVE SAMPLE BLOW COUNT. INDICATES TIIAT 50 BLOWS OF A 14o-POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 3 INCHES.
I PRACÏICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON SEPTEMBER 1, 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. ÏHE 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 (PCf) (ASTM D2216);+4 = PERCENTAGE RETAINED ON No. 4 SIEVE (ASTM 06915);
-2oO= PERCENTAGE PASSING No. 200 SIEVE (ASTM 01140).
21 -7 -683 Kumar & Associates LEGEND AND NOTES Fig. 5
E
!
I
€
e
¡
SAMPLE OF: Cloy ond Silt
FROM:BORING2@^2.5'
WC = 8.0 %, DD = 97 pcf
I
;
l
I
in
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
--i - i.' -'lil rlli
l
ljIr
I
i-l ì-
F
1
i
I
I
I
-'i-l
I
'-'1
I
ìI
i
l
l
l
1
ñ
JJt¡l
=t11
I
z.otr
o
=o
u')z.oc)
0
-1
-2
-5
-4
1.0 APPLIED PRESSURE - KSF 10 t00
21 -7 -683 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
'r
I
I
6
2
100
g0
80
70
ô0
3ô
/ao
30
20
to
o
HYDROMETER ANALYSIS SIEVE ANALYSIS
TIME RËADINOS U.S. SÍANOARO SERIES CLEAR SQUÀRE OPENINGS
---l :f
r¡
I -r -1
-I
- r 'F_
IL
--..1--t
I --.t-
- t -- t-
o
lo
20
50
,to
50
50
70
ao
90
too
-
U
,t ,600 1.18 2.36
2'O
IN MILLIMETERS
132
DIAMETER OF
CLAY TÜ sIL'I COBBLES
GRAVEL 37 % SAND 32 %
LIQUID LIMIT - PLASTICITY INDEX
SAMPLE OF: Slighlly Silty Sondy crovel
SILT AND CLAY 11 %
FROM: Boring 1 O 2,5 & 5 (Combined)
lh€so losl resulls opply only lo thr
sqmplar whlch wrrr l!sl.d. Tho
lasllng raport sholl nol b6 reproduced,
ðxorpl lñ lull, wllhoul ihã wrltlðn
oÞÞrovol of Kumqr & As¡oclolc¡, lnc.
SLive onolysls losllng ls perlormãd ln
qecordqnco wlth ASTM D6913, ASTM D7928,
ASTM C136 ond/or ASTM D1140.
SAND GRAVEL
FINE MEDTUM ICOARSE FINE COARSE
21 -7 -683 Kumar & Associates GRADATION TEST RESULTS Fig. 5
rc iiç1fi',ffiî:ffinl'iiå*'"
TABLE I
SUMMARY OF LABORATORY TEST RESULTS
SOIL TYPE
Slightly Silty Sandy Gravel
Clay and Silt
Clay and Silt
(psf)
UNCONFINED
COMPRESSIVE
STRENGTH
PLASTIC
INDEX
lol I
ATTERBERG LIMITS
lolol
LIQUID LIMIT
68
PERCENT
PASSING NO.
200 stEvE(:/,1
SAND
GRADATION
GRAVEL
f/"1
100
(pcfl
NATURAL
DRY
DENSITY
1132510.5
97
(%l
NATURAL
MOISTURE
CONTENT
8.0
6.2
tftì
DEPTH
2% &.5
combined
.tl/
5
SAMPLE LOCAIION
BORING
1
2
No. 21-7-683