HomeMy WebLinkAboutSubsoil Study for Foundation Design 05.13.2021IC iiç1fi#flf*i*'""Êü'**
An Employcc Ownad Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglørwood@kumarusa. com
www.kurnarusa.com
Offrce Locations: Denver (HQ), P¿rker, Colorado Springs, Fort Collillg Glenwood Springs, and Sumndt County, Colorado
RECEIVED
M:ay I3,202I
Claire Spofford and Rich Leavitt OCT 2 T 2021
4 Tara Road GARFIELD GOUNTY
Essex, Massachusetts}lg2g TOMMUNITYDEVELOPMENT
claire. snoffordØsmai l. com
ri chleavitt I @ gmail. com
Project No.2I-7-332
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 8, Callicotte
Ranch, Callicotte Ranch Road, Garfield County, Colorado
Dear Claire and Rich:
As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations at
the subject site. The study was conducted in accordance with our proposal for geotechnical
engineering services to you dated March 8,2021. The data obtained and our recommendations
based on the proposed construction and subsurface conditions encountered are presented in this
report.
Proposed Construction: The proposed residence will be a single-story wood-frame structure
over a walkout basement level and attached garage located on the site as shown on Figure L
Ground floors will be slab-on-grade. A retaining wall will support the uphill cut side of the auto
court. Cut depths are expected to range between about? to 12 feet. Foundation loadings for this
type of construction are assumed to be relatively light and typical of the proposed type of
construction.
If building conditions or foundation loadings are significantly different from those described
above, we should be notified to re-evaluate the recommendations presented in this report.
Site Conditions: The subject site was a vacant forested lot with a two-track access road along
the southwest side of the lot. The ground surface is gently sloping generally down to the south at
a grade of around 10 to 15 percent in the building area and moderately sloping do'¡¡n to the
south/southeast at a grade of up to 30 percent on the surrounding hillside. Vegetation consists of
dense juniper and pinyon trees and grass. An irrigation ditch is north of the proposecl auto court,
Subsidence Potential: Callicotte Ranch is underlain by Pennsylvania Age Eagle Valley
Evaporite bedrock. The evaporite contains gypsum deposits. Dissolution of the gypsum under
a
certain conditions can cause sinkholes to develop and can produce areas oflocalized subsidence.
During previous rvork in the area, a sinkhole rvas observed about 2,70r.ì feet to the northeast of
Lot 8, outside the Callicotte Ranch development. Sinkholes were not observed in the immediate
area of the subject lot. Dased on our present knowledge of the site, it cannot be said for certain
that sinkholes will not develop. In our opinion, the risk of ground subsidence at Lot 8 is low
throughout the service life of the residence and similar to other lots in the area but the owner
should be aware of the potential for sinkhole development.
Subsurfac.e Conditions: The subsurface conclitions at the site were evaluatecl by excavafing
5 exploratory pits and 2 profile pits at the approximate locations shown on Figu'e 1. The logs of
the pits are presented on Figure 2. The subsoils encountered, below about I to lYz feet of topsoil,
consist of nil to 4 feet of very stiff to hard, sandy calcareous silt and clay underlain by basalt
eobbles and boulders in a highly calcareous sandy silt matrix down to the maximum explored
depth of 7 feet. Refusal to backhoe digging was encountered in the pits as shown on Figure 2.
Results of swell-consolidation testing performed on relatively undisturbed samples of upper clay
and silt soil and sandy silt matrix, presented on Figures 4 and 5, indicate low compressibility
under existing low moisture conditions and light loading and a low collapse potential or minor
expansion potential when wetted. Results of gradation analyses performed on samples of sandy
silt with gravel (minus 3-inch fraction) obtained from the site are presented on Figures 6 and 7.
The laboratory test results are summarizedin Table 1. No free water was observed in the pits at
the time of excavation and the soils were typically slightly moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recorrunend spread footings
placed on the undisturbed natural soil designed for an allowable bearing pressure o?!sl
for support of thc proposcd rcsidcnce. The soils typically tend to comprcss aftcr wctting undcr
load and there could be around l-inch of post-construction foundation settlement depending on
the depth and extent of wetting. Footings should be a minimum width of 18 inches for
continuous walls a¡rd 2 feet for columns. Loose disturbed soils encountered at the foundation
bearing level within the excavation should be removed and the footing bearing level extended
down to the undisturbed natural soils. We should observe the completed excavatton fbr bearing
conditions prior to forrning footings. Exterior footings should be provided with adequate cover
above their bearing elevations for frost protection. Placement of footings at least 36 inches
Kumar & Associates, lnc. o Project No. 21-7-332
IJ
below the exterior grade is typically used in this area. 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 be designed to resist a
lateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site
soil as backfill excluding organics and rock larger than 6-inches.
f,'loor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded
slab-on-grade construction with a differential settlement risk mainly if the subgrade 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 free-draining gravel
should be placed beneath basement level slabs to facilitate drainage. This material should
consist of minus 2-inch aggregate with less than 50o/o passing the No. 4 sieve and less than2%o
passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least95Yo 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.
Underdrain System: 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
heary precipitation or seasonal runoff. Frozen ground during spring runoffcan create aperched
condition. We recommend below-grade construction, such as retaining walls, crawlspace and
basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain
system.
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 I foot below lowest adjacent finish grade and sloped at a minimumlo/oto
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2o/opassingthe 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 TYzfeet deep.
Kumar & Associates, lnc. o Project No. 21-7-332
-4-
SuI{ace Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the residence has been completed:
1) Inurdation of the foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfrll should be adjusted to near optimum moisture and compacted to
at least 95% 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.
Free-draining wall backfill should be covered with filter fabric and capped with
about 2 feet of the on-site, frner graded soils to reduce surface water infiltration.
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 pavement and walkway areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfrll.
5) Landscaping which requires regular heavy irrigation should be located at least
10 feet from the building Consideration should be given to the use of xeriscape
to limit potential wetting of soils below the foundation caused by irrigation.
Septic System Suitability: The USDA gradation testing results presented on Figure 7, indicate a
soil type of 2 or 2A (Silt Loam) for the sample taken from Profile Pit 1. Our experience in the
area and the results from separate classifrcation testing from Pit 2 indicate there could be an
upper clay loam layer. We believe the septic system can be designed for type 2 or 2A soils
provided it is based in the underlying silt loam. A civil engineer should design the infiltration
septic disposal system.
Limitations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this area at 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 pits excavated at the locations indicated on Figure I
and to the depths shor¡¡n on Figure 2, the proposed type of construction, and our experience in
the area. Our services do not inclucle determining the presence, prevention or possibility of mold
or other biological contaminants (MOBC) developing in the future. If the client is concemed
Kumar & Associates, lnc. o Project No. 21-7-332
-5-
about MOBC, then a ptofessional in this special field of practice should be consulted. Our
findirrgs include interpolation and extrapolation of the subsurfaee conditions identified at the
exploratory pits and variations in the subsurtbce conditions may not become evident until
exsavation is performed. If conditions encountered during construction appear different from
those described in this report, we should be notified at once so re-evâluation of the
recommendalions 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 senices during construction to review and
monitor the implementation of our recommendations, and to veri$ that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the rccommenclations presented herein. We reconrmend on-site observation
ofexcavations and foundation bearing strata and testing ofstructural fill by a representative of
the geotechnical engineer.
if you have any questions or if we may be of further assistauce, please let us know.
Respectfully Submitted,
Kurn:rr & ,4.ssociates, Inc.
ytñr¿-þ. panp.a2.z
James H. Parsons, P.E.
Reviewed by:
Steven L. Pawlak,
JIlPlkac
attachments Figure 1 -Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Legend and Notes
F'igures 4 and 5 - Swell-Consolidation Test Results
Figure 6 - Gradation Test Results
Figure 7 - USDA Gradation Test Results
Table 1 - Summary of Laboratory Test Results
Patrick Stuckey - stlrcarsh t?rjcomcast. net
Kumar & Associates, lnc. ¡Project No, 21-7-332
PIT 3
LOT 7 -t
l¡
ó
PIT 2PIT 4 I
" tFRoFTLE PIT-2
PROFIT.E PIT-1 TO CALLICOTTE
RANCH ROAD
I
PIT t
!
I
I
I
ì
l
a
I
I
!
I
I
\
a
,]
a -.1{:t,"'
{I
LOT 8 CALLICOTTE RANCH
APPROXIMATE SCALE-FEET
Fig. 121 -7 -332 Kumar & Associates LOCATION OF EXPLORATORY PITS
Ë
*
¡¡
&
PIT 1
EL. 77'
Pfi2
EL. 6 t'PIT 5
EL. 65
PIT 4
EL, 7'1,
0 0
\NC=1 4.2
DD=88
-200=8 ,|
t-LI
LI
t!
I-t-.-fL
¡¡Jô
-, *4=22, -2OO=49
WC= 13.9
DD=84
-200=83
LL=54
Pl=55
Ft¡J
t¡J
LL
I-t-fL
l¿lô
5 5
10 10
PIT 5
EL. 68
PROFILE PIT 1
EL. 52'
PROFILE PIT 2
EL. 50,
0 0
t-
Ld
L¡Jl!
I-t-o-
t¡Jâ
5 WC=9.9
DD=99 I
WC=8.4
DD=79
-2OA=78
LL=33
Pl=16
5
t-
L¡J
L¡llL
I-FÈl¡l
CI
: GRAVEL=6
I sano=zt
SILT=55
CLAY=20
'10 10
oy'
.,,/.dz.'
ñ
Fî9. 221-7-332 Kumar & Associates LOGS OF EXPLORAIORY PITS
LEGEND
TOPSOll ; ORGANIc SANDY Sll T ANI) Cl AY, MolST, ÊROWN.
slLT ANt) CLAY (ML-CL); SANDY, SCATTERED GRAVEL, VERY STIFF TO HARD, Sl IGHTLY
MOIST, PALEITAN, MODERATELY TO HIGHLY CALCAREOUS, LOW TO HIGH PLASTICITY.
BASALT ROCK AND SILT (GM-ML); COBBLE TO BOULDER SIZE ROCK, HIGHLY CÀLCAREOUS
SANDY S|LT AND CLAY, DENSE/HARD, SLTGHTLY MOIST, GRAY AND WHITE.
HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE
DISTURBED BULK SAMPLE.
PRACTICAL DIGGING REFUSAL.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A MINI EXCAVATOR ON APRIL 16,2021
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SI.{OWN ON THE SITE PLAN PROVIDED,
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY PIT 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 PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7, LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (¡STV O ¿ZZ);
-2Qo= PERCENTAGE PASSING N0. 200 SIEVE (ASTM D 1140);
LL = LIQUID LIMIT (ASTM D 4518);
Pl = PLASTICITY INDEX (ASTM D a318);
GRAVEL = PERCENT RETAINED ON N0. 1 0 SIEVE;
SAND = PERCENT PASSING NO. 1 0 SIEVE AND RETAINED ON No. 525 SIEVE;
SILT = PERCENT PASSING NO. 525 SIEVE T0 PARTICLE SIZE .002MM;
CLAY = PERCENT SMALLER THAN PARTICLE SIZE .002MM.
F
i
I
Fî9.321 -7 -332 Kumar & Associates LEGEND AND NOTES
SAMPLE OF: Sondy Cloyey Silt
FROM:Pil 2@2'
WC = 14.2 %, DD = 88 pcf
-2AO = 81 %
Coñ$llddlil tsuq pldomd In
ôcc6donc. ffi ffi r4ffi.
Kumor ond &sælot-, lnc. *€ìloppfowl of
t:
i
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
t-'l
I
l
i11i
I
, ..1
I
JJul
=an
I
z.otr
o
Jo
l.r)z.oo
0
2
3
4
-5
-6
-7
-8
1 I,O APPLIED PRESSURE - KSF 10 100
21 -7-332 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 4
SAMPLE 0F: SurrrJy 5illy Cl'åy M'rlrix
FROM:Plt5O4.5'
WC = 9.9 Yo, DD = 99 pcf
lnúshoutrdtt n
I
I
l
l
I
I
-l
-ì
j
j
Ì EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
--t
I
l
f
1
i
!
¡
l
l
l
I
t-
l
i
I
I
I
i
il
il
I
ñ
JJ
l¡J
=(n
I
z.otr
ô
=o
aJ',z.o(J
0
I
2
3
4
t.O APPLIED PRESSURE - KSF 10 100
21-7-332 Kumar & Associates SWELL-CONSOLIDATION TEST RTSULTS Fig. 5
I
â
HYDROMETER ANALYSIS SIEVE ANALYSIS
U,S, STANDÆD SERIES CLüR SAUARÉ OPENINçSTIYE READINGS
24 HRS 7 HRS
MN
¡
i
I
t I
t
t
I I
t
1t
t
I i
i
4
100
90
a0
70
60
50
40
20
l0
to
20
30
40
50
60
70
80
90
I
e
foo
.ool -wz
2,OS IN MILLIMETERS
I
DIAMETER OF
CLAY TO SILT COBBLES
GRAVEL 22 % SAND
LIQUID LIMIT
SAMPLE OF: Sondy Silt wilh Grovel
29%
PLASTICITY INDEX
SILT AND CLAY 49 %
FROM; Pil?O3.5'-4.5'
Th.sr l.sl resulls opply only lo lhc
sompl.s whlch w.rê l.slod. Thr
losllng rêporf shsll nol bê reproducad,
exc€pl in full, vilhoul lhe vrltlen
qpprgvql of Kumqr & As€gc¡El€s, lno,
Sllvo qnolysl! lcallng ls pcrform€d in
occordonce wlth ASÎM 06913, ASTM 07928,
ASÍM C156 ond/or ASTM D1140.
SAND GRAVEL
FIN E MEDTUM lCOlnSe FIN E COARSE
21 -7-332 Kumar & Associates GRADATION TEST RESULTS Fig. 6
HYLìH(JME I EH ANIALYSIS SIFVF ANAI YSIS
ÏME READINGS U,9, STANDARD SERIES
#140 #60 #35 #ta +10
CLEAR SOUARE OPENINGS
24 HR, /HB I t/1r,1.
+325
045
#4 s/B 314" 1 100
10 90
20 BO
30 /o
cft¡lz.
Fl¡l
É.
Fz.trlO
É.
l¡J(L
40 60
()
z.
U''tn
TL
Fzbl(JE
L¡J(L
50 50
60 40
70 30
BO 20
sJ0 to
100 9,5 19.0 37,5 76,2 152 203,001 ,002 .005 .009 .019 .045 .106 .025 .500 1.00 2.00 4.75
DIAMETER OF PARTICLES IN MILLIIV1ETERS
CLAY COBBI ES
GRAVEL 6 %SAND 21 %SILT 53 %CLAY 20 %
USDA SOIL TYPE: Silt Loam FROM: Profile Pit 1 @ 6'-7'
/
/
/
/
/
//
/
SILT V F]NE FINE MEOIUIJ
?1 -7 -332 Kulmar & Associates USDA GRADATION TEST RESI.ILTS rig. 7
I(t l*iç1fi*ifffi*$åü**'TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.21-7-332SOIL TYPESandy Clayey SiltSandy Silt with GravelCalcareous Sandy Silty ClaySandy Silty Clay MatrixSiltLoamSandy Silty Clay356IPLASTIC INDEX(w54JJATTERBERG LIMITSLISUID LIMIT(:/;t20CLAY(%)53SILT(%)I2SAND("/ùUSDA SOIL TEXTUREGRAVELlf/"',6SILT&CLAY(%)II498378SAND("/ù2922GRADATIONGRAVEL('/"1NATURAJ-DRYDENSIry(pc088849979t4213 99.98.4NATURALf¡IOISTURECONTENTr:/,1DEPTH(fr)23V2-4Y,2Yz4Y,6-7445ProfilePits12SAIûPLE LOCATIONPIT2