HomeMy WebLinkAboutSubsoil Study for Foundation Design 07.27.2022IIF,T Kumar & Associates, lnc.'
Geotechnical and Materials Engineers
and Environmental Scieniists
An Ëmployee Owned Gompe¡ny
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www.kutnatusa.coln
July 27,2022
Robert Leavitt
P.O.Box 4441
Basalt, Colorado 81621
criglsonconshuctioninc@ gmail.corn
,,"it3ål#:bi?,iffi il'-''-î
Ofïice Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Splings, and Summit County, Colorado
RECEMEN
Subject:Subsoil Study for Foundation Design, Proposed Residence, Lot 31, Mountain
Springs Ranch, Saddleback Road, Garfield County, Colorado 81601
Dear Robert:
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 agreement for geotechnical
engineering services to you dated May 26,2022. 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 log-ftame building with an attached
and a detached garage located on the site as shown on Figure 1" Ground floors could be
structural over crawlspace or slab-on-grade. Cut depths are expected to range between about 2 to
5 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 vacant at the time of our field exploration with a rough-
cut driveway leading to the proposed building area. The ground surface was sloping down to the
east in the proposed building area with a steeper slope above the building arcaand a shallower
slope below the building area. Vegetation consists of scrub oak, sagebrush, grass and weeds. A
stockpile of basalt boulders from the driveway cut was present below the building area.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits and two profile pits at the approximate locations shown on Figure 1. The logs of
the pits are presented on Figure 2. The subsoils encountered, below about/z feet of topsoil,
consist of up to 3%feet of stifl sandy silty clay underlain by sandy silty clay and gravel with
basalt cobbles and boulders down to the maximum explored depth of 8 feet. Results of swell-
..'
consolidation testing performed on relatively undisturbed samples of sandy clay, presented on
Figure 3, indicate low compressibility under existing moisture conditions and light loading and a
low expansion potential when wetted. Results of a gradation analysis performed on a sample of
clayey gravel (minus 3-inch fraction) obtained from the site are presented on Figures 4 and 5.
No free water was observed in the pits at the time of excavation and the soils were slightly moist
to moist.
Foundation Bearing Conditions: Testing of the clay and clay portion of the gravel soils
encountered in the pits at the site generally show low to moderate expansion potential. With the
current information and test results we recommend the foundation bearing levels be sub-
excavated to a depth of at least 2 feet and backfilled with an imported granular material (such as
CDOT Class 6 road base). When the foundation excavation for the building has been cut to
design bearing level, a representative of the geotechnical engineer should evaluate the exposed
material and the need for structural fill to help mitigate the expansion potential.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
placed on at least 2 feet of compacted, imported granular structural fill designed for an allowable
soil bearing pressure of 2,000 psf for support of the proposed structures. The clay soils tend to
expand after wetting and there could be post-construction foundation movement of around 1 to
2 inches depending on the soil conditions. Footings should be a minimum width of 16 inches for
continuous walls and 2 feet for columns. Topsoil and 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. Exterior footings should be provided with
adequate cover above their bearing elevations for frost protection. Placement of footings at least
36 inches below the 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 feet. Foundation walls acting as retaining structures should also
be designed to resist alateral earth pressure based on an equivalent fluid unit weight of at least
60 pcf for the on-site soil as backfill.
Floor Slabs; The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded
slab-on-grade construction with a risk of heave and building distress. Sub-excavation of the clay
soils at least2 feet and replacement with structural fill may be warranted to help mitigate the
expansion potential. To reduce the effects of some differential movement, floor slabs should be
separated frorn all bealing walls and colunns with expansion joints which allow unreshained
Kumar & Associates, lnc. @ Project No. 22-7-400
-3-
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 than2Yo passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill should consist of
imported granular soils devoid of vegetation, topsoil and oversized rock.
Underdrain System: Although free water was not encountered in the exploratory pits, it has
been our experience in mountainous areas and where there are clay soils that local perched
groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground
during spring runoff can 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 1 foot below lowest adjacent finish grade and sloped at a minimum l%o to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2Yo passing the 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 and covered
with filter fabric such as kfirafi l40N and 160N.
Surface Drainage: 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. Drying could increase the expansion potential of the clay
soils.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95Yo of the maximum standard Proctor densiqi in pavement and slab areas
and to at least 90o/o of the maximum standard Proctor density in landscape areas.
Free-draining wall backfill should be covered with filter fabric and capped with
about2 feet of the on-site, finer graded soils to reduce surface water infiltration.
Kumar & Associates, lnc. @ Project No. 22-7-400
-4-
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. A swale may be
needed uphill to direct surface runoff around the residence.
Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Landscaping which requires regular heavy irrigation should be located at least
10 feet from the building.
4)
s)
Septic Disposal Area: Two Profile Pits were dug at the locations shown on Figure 1. The
subsurface profile mainly consists of gravelly sandy loam or gravelly clay loam. Results of
USDA gradation tests performed on samples of the soils are shown on Figures 7 andS and the
test results are summarized on Table 1. Based on these findings, the tested area should be
suitable for an infiltration septic disposal system. A civil engineer should be engaged to design
the 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 1
and to the depths shown on Figure 2,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 pits and variations in the subsurface conditions may not become evident until
excavation is performed. If conditions encountered drning construction appear 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 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 verify that the recommendations
have been appropriately interpreted" Significant design changes may require additional analysis
Kumar & Associates, lnc. @ Project No. 22-7-400
-5-
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.
If you have any questions or if we may be of further assistance, please let us know.
Respectfu lly Submitted,
WââK{âxr & &ççqþæâøteß, âwe.
þ'"firr 3¡7@
James H. Parsons, P.E.
Reviewed by
Daniel E. Hardin, P
JHPlkac
attachments Figure I -Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Legend and Notes
Figures 4 and 5 * Swell-Consolidation Test Results
Figure 6 - Gradation Test Results
Figures 7 and 8 - USDA Gradation Test Results
Table 1 - Summary of Laboratory Test Results
Kumar & Associates, lnc, e Prajee-t 1'lo. 22.7 -48û
$il& rrsïrr {fiaFr0H* *lt¡¡Yfl{
rËffior*æ IffiffitÊ f ñåilffi æ It tr l¡t{F ll Ít ülff {É,u*
¡L¡N lìF ffif st!Åc.17,îã ffnEt
%
lr{*,t{rilH sPfttffi Ëåf{st Lü?xt
$
'EfifiTÐ
+4,
PIT 1Lm *$n
miffiE
T@:æ*
T
PIT 2
Iktâr 3+pif
PP-lr ilil$
PP-2
25 50
APPROXIMATE SCALE-FEET
\
LOCATION OF EXPLORATORY PITS Fig. 122-7 -400 Kumar & Associates
PIT 1 PIT 2 PP- 1 PP*2
0 0
tNC=22.9
DD=98
F
t¡.,1LItL
IIF-(L
tdo
t-
L¡Jl¡lt!
I-F-(L
tJlo
WC=30.2
DD=86
5 Ã
10 10WC=8.6
+4=29
-200=65
*4=53
-200=56
GRAVEL=2
SAND=20
SILT=28
CLAY=50
WC=29
*4=41
-200=30
GRAVEL=3
SAND=40
SILT=14
CLAY='l 3
22*7 -400 Kumar & Associates LOGS OF EXPLORATORY PITS Fis. 2
Ê
I
T
LEGEND
TOPSOIL. SAND, SILT AND CLAY, ORGANIC, FIRM, MOIST, DARK BROWN.
CLAY (CL): SANDY, SILTY, STIFF, MOIST, RED BROWN
GRAVEL AND CLAY (GC-CL): COBBLES, BOULDERS, SANDY, SILTY, STIFF,
MOIST, RED BROWN, BASALT ROCK.
F
t
HAND DRIVE SAMPLE.
DISTURBED BULK SAMPLE.
I PRACTICAL DIGGING REFUSAL.
NOTES
I. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JUNE 22, 2022
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPTH.
4. THE EXPLORATORY PIT LOCATIONS 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.
a LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D
-200= PERCENTAGE PASSING NO. 200 SIEVE
GRAVEL = PERCENT RETAINED ON NO. 1 SIEV
(ASTM
E
D1 1
a22);
a0);
SAND =PERCENT PASSING NO. 1O SIEVE AND RETAINED ON NO.325 SIEVE
SILT = PERCENT PASSING NO. 325 SIEVE TO PARTICLE SIZE .002MM
CLAY= PERCENT SMALLER THAN PARTICLE SIZE .002MM
22-7 -400 Kumar & Associates LEGEND AND NOTES Fis. 3
3
SAMPLE OF: Sondy Cloy ond Grovel
FROM:Pit1@5.5'
WC = 30.2 %, DD = 86 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
II
)
(
ftê36 têst rêsulb oppt oñly to th.
sompl€s l$têd. th€ tostlng ropoñ
lholl not b€ r6Þrduc€d, exc.pt ln
full, rlthout ths sltt6n opprovol of
Kumor ond ßsoclotãs. lnc. SHêll
Consol¡dotlon t$thg pêlomed ¡n
d.¿ôrdôñ.ê wìlh Ás D-4546.
2
1
JJ
LJ
=U''
I
z.otr
ô
Jo
U)z.o()
0
-1
2
1.0 APPLIED PRESSURE - KSF f0 100
22-7 -400 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
Ê
I
SAMPLE OF: Sondy Cloy
FROM: Pit 2 @ 1.5'
tNQ = 22.9 %, DD = 98 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
I
I
fh6s€ tæt rêsultå oppt only to th6
tompl€s te3tèd. Thå testiñg repoÉ
rholl not b. raDroduc€d. €¡c6Þt In
Iull, wlthout tho wdttln opprovol of(úmor oñd /A$ocìoles, lnc. sçêll
Sonsolldotlon t€stlng pedoñ6d ln
rccordonco wlth ffi D-646.
1
0
JJ
t¡J
=ln
I
zotr
o
=oØzoo
-1
-2
-3
-4
-5
1.0 APPLIED PRESSURE - KSF IO 100
22-7 -400 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 5
t
I
e
€
¡
HYDROMETER ANALYSIS SIEVE ANALYSIS
CLAR SQUARE OPENINGSU.S. STANDARD SERIESfIME REAOINC5
24 HFS 7 HRS I út{
d
100
90
ao
70
60
50
40
30
20
t0
o
o
t0
20
30
40
50
60
70
ao
90
Íoo
I
,oo5 .o09 .ot 1.73
DIAMETER OF
.125
PARTICLES IN
CLAY TO SILT COBBLES
GRAVEL 29 % SAND
LIQUID LIMIT
SAMPLE 0F: Grovelly Silly Cloy
6 %
PLASTICITY INDEX
SILT AND CLAY 65 %
FROM:Pil2@5'-6'
Ih€sc lôsl rcsulls opply only lo lh6
somplos whlch wor€'loslod. 'Ih€
losl¡ng ¡eport sholl nol bo reproduc.d,
.xccpt lñ full, wllhoul lh. wrlllon
opprovol of Kumor & Assoclolos, lnc.
Slôvô qnqlysls l6sllng ls p.rform.d ln
occordonco wlth ASTM 06913, ASTM 07928,
ASTM C136 ondlor ASTM Dll40.
GRAVELSAND
COARSE FINE COARSEFINEMEDIUM
22-7 -400 Kumar & Associates GRADATION TEST RESULTS Fig. 6
e
I
ás
s
4
r
â
SIEVE ANALYSISHYDROMETER ANALYSIS
STANDARD SERIES CLEAR SQUARE OPENINGS
24 HB, 7 HR I MIN,
+325 #140 #60 #35 #4 3" 5" 6" B"
045 100
10 90
20
30 70
o
Ldz.
F
LiJ
É.
Fz.
LiJ(J
É.LI
o_
40 60
(9
z.
tt)
an
(L
F-z
t¡J()
É.td
o-
50
60 40
70 30
80 20
90 10
100 0.001 .002 .m5 .009 .01s .045 .106 .025 .500 1.00 2.00 4.75
DIAMETER OF PARTICLES IN MILLIMEÏERS
9.5 19.0 31.5 76.2 152 203
cuY COBBLES
GRAVEL 33 %SAND 40 % SILT 14 %CLAY 13 %
USDA SOIL TYPE: Grovelly Sondy Loom FROM: PP-1 @ 3'-4'
ti-
ti
......................
-
'-t,-,,.,
SAND
SILT V. FINE FINE
USDA GRADATION TEST RESULTS Fig.722-7 -400 Kumar & Associates
p
SIEVE ANALYSISHYDROMETER ANALYSIS
TI SERIES
+18 #10
CLEAR SOUARE OPENINGS
24 HR. 7 HR 1MIN,
#325 #4 3/8" 314', 1 1/2',5" 6" 8"#140 #60 #35 100
't0 90
20 BO
30 70
ôLIz
t-tJÉ
Fz
TJ
C)É.
LrJ
o_
40
()
z.
tn
U''
o-
Fz.LI()
É.
L¡J(L
50
60 40
70 30
80 20
90 10
100 0.00't .002 .005 .009 .019 .045 106 .025 .500 1.00 2.00 4.75 9.5 19,0 37.5 76.2 152 203
DIAMETER OF PARTìCLES IN MILLIMETERS
CLAY COBBLES
GRAVEL 22 %SAND 20 %SILT 28 %CLAY 30 %
USDA SOIL TYPE: Grovelly eloy Loom FROM: PP-1 @ 5'-6'
ii-i i
.-,..., ,,,t. .. ....t. t-- .---..
GRAVEL
SILT V FINE FINE I\¡EDIU[,4 COAFSE
Fig. 822-7 -400 Kumar & Associates USDA GRADATION TEST RESULTS
l(t t iåffiT['ittr$tr*'""Êü'**TABLE 1SUMMARY OF LABORATORY TEST RESULTSect No. 22-7-400Gravelly SiltyClavGravelly SandyLoamGravelly ClayLoamSOIL TYPESandy Silty Clayand GravelSandy Silty ClayI330CLAY(%)I428SILT(%)4020SAND(f/,)JJ22USDA SOIL TEXTUREGRAVELti/"|65(%)SILT&CLAY6SAND(%)GRADATIONGRAVEL(%)29NATURALDRYDENSITY(pc0869830.222.98"616NATURALMOISTURECONTENTV"l3-45-6(ft)DEPTH3%t%5-612ProfilePit 1SAMPLE LOCATIONPIT