HomeMy WebLinkAboutSubsoils Study for Foundation Designl(+tt$ffiix$**
An Emptsyac {hrn*d Ccmpsny
5020 County Road 154
Glenrvood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
enrai I : kaglenrvood(!kurnalusa.com
wwwkumarusa. conl
Offics Locations: Denver (HQ), Parker, Colorado Splings, Fort Collins, Glenwood Springs, and Surnrnit Count5,. Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT D-24, ASPEN GLEN SURDIVISION
52 ELK TRACK LANE
GARFIELD COUNTY, COLORADO
PROJECT NO.24-7-124
MARCH 25,2024
PREPARED FOR:
TRANSWBST CONSTRUCTION
ATTN: MIKE SCRIVBNS
P.O. BOX 2325
GYPSUM, COLORADO 81637
mike@tran srvestconstru ction.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION ......
SITE CONDITIONS
SUBSIDENCE POTENTIAL
FIELD EXPLORATION .,...
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS ....
DESIGN RECOMMENDATIONS ................
FOUNDATIONS
FOUNDATION AND RETAINING WALLS ......
FLOOR SLABS
SURFACE DRAINAGE................
LIMITATIONS...
FIGURE I . LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINCS
FIGURE 3 . LEGEND AND NOTES
FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS
TABLE I - SUMMARY OF LABORATORY TEST RESULTS
1
I
I
-4-
..-2-
n
-3-
...- 8 -
Kumar & Associates, Inc, o Project No. 24-7-124
PURPOSE AND SCOPE OF STUDY
This report plesents the results ofa subsoil study for a proposed residence to be located on Lot
D-24, Aspen Glen Subdivision, 52 Elk Track Lane, Garfield County, Colorado. The project site
is shown on Figure 1. The pulpose of the study was to develop recommendations fbr foundation
design. The study was conducted in accordance with our agreement fbr geotechnical engineering
services to Transwest Construction dated January 23.2024.
A field exploration program consisting of exploratory borings rvas 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 analyzed to develop recommendations for foundation types, depths and allowable
pressures lbr the proposed building foundation. This report suttmarizes the data obtained during
this study and presents our conclusions, recornmendations and other geotechnical engineering
considerations based on the proposed construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
The residence will be a single-story wood frame stnrcture over crawlspace with an attached
g^rage with a slab-on-grade floor. Grading for the structure is expected to be relatively minor
with cut depths between about2% to 4 feet. We assunre relatively light foundation loadings,
typical of the proposed type of construction.
lf building loadings, location or grading plans are significantly different from those described
above, we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDTTIONS
LotD-24 was vacant at the tirne of our field exploration and there was about 2 inches of snow
covering the ground surface. The lot is located off the Elk Track Lane cul-de-sac to the north,
Kumar & Associates, lnc. @ Project No. 24-7-124
see Figure L Along the south side of the lot is an inigation ditch and easement. The ground
surface in the building envelope is relatively flat with a gentle slope down to the south. There is
about 1 to 2 feet of elevation difference across the assumed building footprint.
SUBSIDENCE POTENTIAL
Bedrock of the Perursylvanian age Eagle Valley Evaporite underlies the Aspen Glen
development. These rocks are a sequellce of gypsiferous shale, fine-grained sandstone and
siltstone with some massive beds of gypsurn and limestone. There is a possibility that massive
gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the lot.
Dissolution of the gypsllm under certain conditions can cause sinkholes to develop and can
producc arcas of localized subsidence. During previous work in the area, several sinkholes were
obsewed scattered througlrout the Aspen Glen Development, rnainly east of the Roaring Fork
River. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in
areas of the Eagle Valley. The closest rnapped sinkhole to Lot D-24 is located about 750 l'eet to
the west. The perimeter of a broad subsidence area that contains the sinkhole is about 250 feet
from the lot.
Sinkholes were not observed in the at 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 oru present knowledge of the subsurface conditions at the site,
it cannot be said for certain that sinkholes will not develop. The risk of firture ground subsidence
on Lot D-24 throughout the seruice life of the proposed residence. in our opinion, is low and
similar to other nearby platted lots: however, the owner should be made aware of the potential
for sinkhole development. lf fLulher 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 February 28,2024. Two exploratory
borings were drilled at the locations shown on F-igure I to evaluate the subsurf'ace conditions
Kumar & Associates, lnc. @ Project No. 24-7-124
1
-_l
The borings were advanced with a 4-inch diameter coutinuous flight auger powered by a truck-
mounted CME-45B drill rig. The borings were logged by a representative of Kumar &
Associates.
Samples of the subsoils were taken with a 2-inch LD. Califomia type liner sampler. The sampler
was driven into the subsoils at various depths with blows fi'om a 14O-pound hammer tblling 30
inches. This test is similar to the standard pcnetration test described by ASTM Method D-1586.
The penetration resistance values are an indication of the relative density or consistency of the
subsoils. I)epths at which the samples were taken, and the penetration resistance values are
shown on the Logs of Exploratory Borings, Figure 2. The samples were returrred to our
laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface profiles encountered at the site are shown on Figure 2. Below
about 6 inches of topsoil, the subsoils consisted of liom about 5% to 9% feet of stiff to very stiff,
sandy to very sandy clay overlying relatively dense, silty sandy gravel and cobbles with probable
boulders down to the drilled depths of 8% and 13 feet. Drilling in the dense coarse granular soils
with auger equipment was difficult due to the cobbles and boulders and drilling refusal was
encountered in both borings in the deposit.
Laboratory testing performed on samples obtained during the field explolation included natural
moisture content and density, percent finer-than-sand-size gradation arialyses, and unconfined
compressive strength. The results of swell-consolidation testing perfonned on samples of the
clay soils, presented on Figures 4, indicate low compressibility under relatively light surcharge
loading and a minor to low expansion potential when wetted under a constant light surcharge.
The unconfined compressive strength testing on a sample of the clay (Boring2 at9') showed
very stiff consistency. The laboratory testing is summarized in Table I '
No groundwater was encountered in the borings at the tirne of drilling and the subsoils were
slightly moist to moist.
Kumar & Associates, lnc. o Project No, 24-7-124
-4-
F'OUNDATION BEAR.ING CONDITIONS
The clay soils encountered at the site have low bearing capacity with variable settlement/heave
potential when wetted. The exparmion potentials measured in the clay samples are believed to be
anomalies, based on our experieuce in the area. The underlying dense gravel and cobble soils
possess moderate bearing capacity and relatively low settlement potential. Spread footings
placed on the upper clay soils, expected to be encounteled at shallow foundation excavation
depth, can be used for foundation supporl of the residence with some risk of movement. 'fhe risk
of movement is primarily if the bearing soils were to become wetted and precautions should be
taken to prevent wetting. Surface runofl landscape imigation, and utility leakage are possible
sources of rvater lvhich could cause wetting. The foundation bearing soils should be further
evaluated for expansion potential at the time of construction.
A lower risk of fbundation moventent would be to extend the foundation bearing down to the
relatively incompressible coarse granular soiis such as by piles or piers. Provided below are
recommendations for spread footings bearing on the clay soils with some risk of movement. If
recommendations for piles or piers are desired, we should be contacted.
DESIGN RECOMMENDATIONS
FOLTNDATIONS
Considering the subsurface conditions encountered in tlre exploratory borings and the nature of
the proposed construction, we believe the building can be founded with spread footings bearing
on natural clay soils with some risk of movement. Precautions should be taken to prevent
wetting of the bearing soils.
The design and construction criteria presentcd bclow should bc obscrvcd for a sprcad footing
foundation system.
1) Footings placed on the undisturbed natural soils should be designed fbr an
allowable bearing plessure of 1,500 psf.
Kumar & Associates, lnc. @ Project No, 24-7-124
5
2)Based on expedence. We expect the initial settlement of footings designed and
corstruoted as discussecl in this section will be up to about 1 inch. There could be
additional movement of about % to L inch if the bearing soils become wetted.
The footings should have a minimum width of 16 inches for continuous footings
and 24 inches for isolated pads.
Continnous foundation walls should be reinforced top and bottom to span local
anornalies and limit the risk of differential movement. One method is to design
tlre {bundation wall to span an unsllpported length of at least 12 feel. Foundation
walls acting as retaining structures should also be designed to resist a lateral earth
pressure as discussed in the "Foundation and Retaining Walls" section of this
report.
Exterior footings and footings beneath unheated areas shonld be provided with
aclecluate soil cover above their bearing elevation for fi'ost protection. Placement
of foundations at least 36 inches below the exterior grade is typically used in this
afea.
Prior to the footing constnrction, any existing fill, topsoil, and loose or disturbed
soils should be removed, and the footing bearing level extended down to firm
natural soils. The exposed soils in footing areas should then be moistened and
compactecl.
A representative ofthe geotechnical engineer should observe all footing
3)
4)
s)
7)
excavations prior to concrete placement to bearing
FOTINDATION AND RETAINING WALLS
Foundation walls and retaining structures which are laterally suppofted and can be expected to
undergo only a slight amount of deflection should be designed for a lateral earth pressure
computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting
of the on-site fine-grained soils. Cantilevered retaining structures which are separate from the
residence and can be expected to cleflect sufficiently to mobilize the full active eafih pressure
oondition should be designed for a lateral earth pressure computed on the basis of an equivalent
6)
Kumar & Associates, lnc. o Project No. 24-7-124
-6-
fluid unit weight of at least 45 pcf for backfill consisting of the on-site soils. Backfill should not
contain vegetation, topsoil, or oversized rocks.
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 sruface. The buildup of water behind a wall or an upward sloping backfill snrfaoe will
increase the lateral pressure imposed on a foundation wall or retaining structure. Au underdrain
should be provided to prevent hydrostatic pressure buildup behincl walls.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at a moisturo content near optimum. Backfill in pavement areas should
be compacted to at least 95% of the maximum stanclard Proctor density. Care should be taken
not to over-compact the backfill or use large equipment near the wall since this could cause
excessive lateral pressure on the wall.
The lateral resistance of foundation or retaining rn'all 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 tlre bottoms of the footings can be calculated
based on a ooefficient of fi'iction of 0.35. Passive pressure of cornpacted backfill against the
sides crf the for.rtings can be calculated using an equivalent fluicl unit weight of 325 pcf, The
coefficient of fiiction and passive pressure values recornmended above asslune ultimate soil
strength. Suitable factors of safefy 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 ofthe footings to resist lateral loads can consist ofthe onsite soils or base course and
should be compacted to at leastglYo of the maxirnum standard Proctor density at a moisture
coutent near optimum.
FLOOR SLABS
The uatural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade
constntction. The clay soils have variable settlement/heave potential when wetted which could
Kumar & Associates, lnc. @ Project No, 24-7-124
-7 -
result in some slab movement if the subgrade soils become wet. Providing a IYz feet depth of
CDOT Class 5 or 6 aggregate base course below the slab should be done to reduce the risk of
floor slab rnovetnent and distress.
To reduce the effects of some differential movement, nonstnrctural floor slabs should be
separated from all bearing walls and columns with expansion joints which allow unrestrained
vertical rnovement. Interior non-bearing partitions resting on floor slabs should be provided with
a slip joint at the bottom of the wall so that, if the slab moves, the movernent cannot be
transmitted to the upper structure. This detail is also important for wallboards, stairways and
door frames. Slip joints which will allow at least 1%-inches of vertical mo\.ement are
recommended. Floor slab controlioints should be used to reduce darnage due to shrinkage
cracking. Slab reinforcement and control joints should be established by the designer based on
experience and the intended slab use.
All 11ll matedals fbr support of floor slabs should be compacted to at least 90% of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site soils devoid of topsoil, and oversized rock, or of imported aggregate base course.
SURFACE DRAINAGE
A perimeter lbundation drain around shallow crawlspace areas (less than 4 feet deep) should not
be needed with adequate compaction of foundation wall backfill and positive surface drainage
away from foundation walls. The following drainage precautions should be observed during
construction and maintained at all times after the residence has been completed:
1) Excessive wetting or drying of the foundation excavations and underslab areas
should be avoided during construction.
2) Exterior backfill should be adjr,rsted to near optimum moisture and compacted to
at least 95o/o of the maximum standard Proctor density in pavement areas and to at
least 90% of the maximum standard Proctor density in landscape areas.
Kumar & Associates, lnc. @ Project No. 24-1-124
-B-
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 minimun slope of
3 inches in the first l0 feet in paved areas.
Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Landscaping which requires regular heavy irrigation, sush as sod, and sprinkler
heads should be located at least 10 feet from foundation walls. Consideration
should be given to use of xeriscape to leduce the potential for wetting of soils
below the building caused by inigation.
4)
LIMITATIONS
This study has been conducted in accordance with gencrally aocepted geotechnical engineering
principles and practices in this area at this time . We make no rvarranty either express or implied.
The conclusions and recommendations submitted in tliis report are based upon the data obtained
fi'om 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 arrd variations in the snbsurf'ace
conditions rnay not become evident until excavation is perforrned. If conclitiorrs encountered
during construction appear to be different from those described in this report, we should be
notified at once so re-evaluation of the recommendations may be made.
This report has been prepared for the exclusive use by our client tbr design purposes. We are not
responsible for technical interpretations by others of our information. As the project evolves, we
should provide continlred consultation and field services during construction to review and
tnonitor the implementation of our recommendations, and to verify that the recolnmendations
have been appropriately interpreted. Signilicant design changes may require additional analysis
s)
Kumar & Associates, lnc. @ Project No. 24-7-124
-9-
or modifications of the reccmmendations presented herein. We recommend on-site observation
of excavations and foundati<ln bearing strata and testing of structural fill by a representative of
the geotechnical enginoer.
Respectfully Submitted,
Kurnar & Ass**int*$, l*ff"
David A. Noteboom, StaffEngineer
Reviewed by:
David A. Young, P.E.
DANnjf
g22l
E'"8
X*rner & Asssciates, f*r.."Projeet l**.:4,?-'!?4
t
s
s
$11,[-&*
i,:utnu'
D{
't* \
Monhal€ \e
I'\
VollEy
-sp- I
t \ru*
\ ..-\\ BORING 1 \
,J _----C$ncreteDriw l-ot !l-23Snss
time ol 41.Ii
Did n6t find
Hoter {:ilrb stgp
i:'
-,t{i #,?'jjt
J-*,-"" '--"-151135* o""
l,"t A# frg'f
t5.liC5 liq ii
/.b ut4tty, urd,n(
Utility FilrFp?,
[{s6e€nt
t/' Jj'"1 :i
f,r 5? r.
o I
ING
7.5" Uilllly,
0rolns$e &
Utility P!rposs$
EoseRant
\t*
\
\-€"t t"oth if D;ls
4,
\-
'_-l
**t$pc d4& ild, 39t^rt
It$ly Pl.riJ/lU t?4P,
'0. 1, ustMc A \
8f48'f{" If\.'Ai?r?/rvtr CrtwtrfSU/P glR rt
Pf8rr{r\r,Vf lrr dlt$r'CR.t /1F,
?;ltr l{srfi/fdf. cY}$dflrusyr
rs frt{drdlnr'*ivr
7.5' Ulftity,
$rainagd &
i.ltlllty Purpis$B
Ia$s$nt
/{,f../a'..'i {} l.
"t
-"f1-' "#iw?i/-4tfi/tridr/^12.$' nrr,rgge &
lrigrtiqr a:6$s6dnt
'E P'JnIII: ANB FRIVATT
.,.1,
2002040
APPROXIMATE SCALE-FEET
24-7 -124 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
j
BORING 1
EL. 6,075'
BORING 2
EL. 6,076'
0 0
46/12
23/12
WC=8.0
DD= 1 05
-200=84
q 27 /12
WC=10.8
DD= 1 00
12/ 12
1O/ 12
WC= 1 6.1
DD=1 1 2
-2QO=79
5 F1!
trJ
L!
I-F(L
Ldo
F
tr.!
Lrll!
I-F
It!o 15/ 12
WC= 1 4.6
DD=115
UC=3,800
10 10
15 15
24-7 -124 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
t
LEGEND
TOPSOIL; SANDY CLAY WITH SCATTERED GRAVEL, ROOTS AND ORGAN|CS, FtRM, MO|ST,
BROWN AND RED BROWN.
CLAY
MOIST
(ct-); snn0y ro vERy sANDy, ScATTERED GRAVEL, SIFF To vERy sTtFF, sLtGHTLy
TO MOIST, RED BROWN.
F:A
h4l cRAVEL AND coBBLEs (ev); pRoBABLE BoULDERS, sANDy, stlTy, occAStoNALLy cLAyEy,
[x]orNse , sLtcHTLy MotsT, MtxED RED AND cRAy BROWN.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
a5112 DRIYE SAMPLE BLOW COUNT. INDICATES THAT 46 BLOWS OF A 14O-POUND HAMMER'-, ._ FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
I enacrrclr- AUGER DRTLLTNG REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON FESRUARY 2E,2024 WIIH 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 TXPLORATORY 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) (ASTU D2216);
-200= PERCENTAGE PASSING No. 200 STEVE (ASTM Dt14o);UC = UNCONFTNED coMPRESSIVE STRENGTH (psf) (ASTM D z1 66).
24-7 -124 Kumar & Associates LEGEND AND NOTES Fig. 3
c
SAMPLE OFr Sandy Cloy
FROM:Boringl@4'
WC = 1 A.8 %, DD = 100 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
1
>q
JJL!
=a
I
zotr
o
=oazo()
2
1
0
-1
-2
1.0 URE - KSF 10
>e
J
J
IJ
=a
I
z.otr
cl
Joazoo
I
0
-1
1 APPLIED PRESSU 100
SAMPLE OF: Sondy Cloy
FROM:Boring29-2'
WC = 8.0 "A, DD = 103 pcf, -2Oo = 84 %
-<
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
Thc
24-7 -124 Kumar & Associates SWELL*CONSOLIDATION TEST RESULTS Fig.4
C
<1
*
K4nffi#,ffi,rr***
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.
SOIL TYPE
Sandy Clay
Sandy Clay
Sandy Clay
Sandy CIay
{psfl
UNCONFINED
COMPRESSIVE
STRENGTH
800-'t
PLASTIC
INDEX
t%\
ATTERBERG LIMITS
t%t
LIQUID LIMIT
P:RCENT
PASSING NO.
200 slEvE
84
79
SAND
(%)
GRADATION
(%)
GRAVEL
NATURAL
DRY
DENSITY
(pcfl
100
i03
112
113
(o/"\
NATURAI
MOISTURE
CONTENT
10.8
8.0
16.1
14.6
{ft}
OEPTH
4
2
7
9
SAMPLE LOCATION
BORING
I
2