HomeMy WebLinkAboutSubsoils Report for Foundation DesignrcA$jffi,Fffffiffi:l:-i**
A* EmBtoyee Swned CcnTpuny
5020 Counly Road 154
Glenwood Springs, CO 81601
phone: {970) 945-7988
fax: (970) 945-8454
etraii: kagienwooci(4kuinarusa.corir
www.kurnatusa. com
Otfice Locations: Denver ft{Q), Parker; Colorado Springs, Fort Collins, Glenwood Splings, and Sumrrit County, Colotado
June 30, 2021
Louise Marron
P.O. Box 157
Carbondale, CO 81623
Iamamon42 I (Ehotmail. com
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Project No. 21-7-331
Subject Subsoil Study for Foundation Design, Proposed Residence, Lot7, Mountain
Springs Ranch, Mountain Springs Road, Garfield County, Coiorado
Ms. Marron:
As reeuested. Kumar & Associates. Inc. oerformed a subsoil shldv for design of foundations at
the subject site. The study was conducted in accordance with our agreement for geotechnical
engineering services to you dated Aprit4,2021. The data obtained and our recommendations
based on the proposed construction and subsurface conditions encountered are presented in this
reporl.
Proposed Construction: The proposed construction consists of a new residence located about
100 feet north of the existing cabin on the lot as shown on Figure 1. Ground floors could be
slab-on-grade or shuctural over crawlspace. Cut depths are assumed to range between about 3 to
.. F=-4 r1....'.J-1:.-.. 1,'..J.!=--. 1'-.1- ila;: !,,..= ,-!-.....-+.-..-) ^ t ! t- I .: .r'. !1.,!=+ .,'".!J iitEL. i-rtUjiiiaLiLtiI iLriiGiiiBJ iiJi LriiJ iJPC iji iJLtiisiIiii-atiJli iiiC l;sbi-iiiiC,-i ii.t ijr.: iUiAtlV'JiJ iiB.iii iiiiij
typicai 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 repofi.
Site Conditions: The subject site was rnostly native hillside terrain at the time of oru site visit.
The ground surface is moderately sloping down to the west at a grade of about l5% with about
5 feet of elevation difference across the proposed building footprint. Vegetation consists of
scrub oak stancis with grass and weed meadows.
Subsurface Conditions: The subsurface conditions were evaluated by excavating 2 exploratory
pits in the designated building site and 2 profile pits in the designated septic disposal site at the
approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The
subsoils encountered, below about 2 to 3 feet of topsoil, mainly consist of sandy clay with
scattered gravel and cobbles to the typical explored depth of8 feet. Pit 3 encountered sandy clay
with basalt cobbles and scattered boulders at about 7 feet to the pit depth of 91A feet. Results of
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swell-consolidation testing performed on relatively undisturted samples frorn the exploratory
pits, presented on Figures 3 and4, indicate low compressibility under existing moisttue
conditions and light loading and a low to moderate expansion potcntial whcn wcttcd. No flcc
water was ohseled in the pits (except for slight seepage at 2 feet in Pit 1) and the soils were
moist to very moist.
F"nundqfi+n Rperinrr (-o4rlifirrrrc. Tcclinry nf t!.n nlnrr enilq frlrn f*nrn thn nifc at flrn eifn.'..:'...b
generally show low to moderate expansion potential. With the current information and test
results, we recommend the foundation areas be sub-excavated at least 2 f'eet below design
bearing level and backfilled with imported, relatively well graded granular material (such as
CD+T Clsss 6 r+*d blse). \.44ren the fc';::dctiii-$ ssc3','stic:r fcr :!re br:ildir:g has l:ee. c'"* tL.
design bearing level, a representative of the geotechnical engineer should evaluate the exposed
soils for the need to sub-excavate and place structural fill to help mitigate the expansion
potential. A low movemeut lisk option would be tu exteld the fouldatiun liearing duwn to a
,!--fl.,-4'r-.-!.!i,...-1.'.i-!-!.- '-'-.';-4,'.'^.^-*,j-nl ."-l- -. '.'!t!-,,"-i--- *i!^- -^.-;!-!,, -,-^,,,-J 1r'! f.-,-+ J^^*ulPLir wi. i !i+L. I viJ ulsvrv rrrvroL4iL 9uiiL!ilL Juuii dJ /trLIi iiiii.,iii -Piivu Pvuuiiiit liiuLuiir tv rwwi uwwP,
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nafure of the proposed conshrrction, we recommend spread footings
placed on at least 2 feet of irnported granular structural fiIl designed for an allowable soil bearing
pressure of 2.000 psf for support of the proposed structure. The clay soils tend to expand after
wetting and there could be post-construction foundation movement of around I to 2 inches
depending on the soil conditions and depth of wetting. Footings should be a rninirnum width of
16 inches for continuous walls and 2 feet for columns. The topsoil, recommended depth of clay
sub-excavation and loose disturbed soils within the footing areas should be removed to expose
the undisturbed natural soils fill should be placed in thin lifts and compacted to at
moishrre content. Exterior footings shouldleast 98% ofstandard Proctor density atneat
be provided with adequate cover above their bearing elevations fbr fi'ost protection. Placement
offootings at least 36 inches below the exterior grade is typically used in this area. Contrnuous
foundation walls should be heavily reinforced top and bottom to span local anomalies such as by
assuming an unsupporfed length of at least 12 feet. Forurdation walls acting as retaining
skuctures should also be designed to resist alaterul earth pressure based on an equivalent fluid
unlt welght or at ieast bU pcr tor me on-srte soii as bact<trtt excluding topsorl and rock larger thall
6 inches.
Floor Slabs: The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded
-qlah-+n-g1a.de ecestn-teti+a with e r!sk- cf heave a."nd buildine dlst{ess. Suh-eseava,tion of tlre elav
Kumar & Assoeiates, lnc. 6 Project No. 21-7-331
-3-
soils at least 2 feet and replacement with skuctural fiIl should be provided to help mitigate the
ireave potential or a structural floor above crawispace should be used. To reduce the effects of
some differential movement, floor slabs should be separated from all bearing walls and columns
with expansionioints which allow unrestrained vertical movement. Floor slab control joints
should be used to reduce damage due to shdnkage cracking. The requirements for joint spacing
and slab reinforcement should be established by the designer based on experience and tire
intended slab use. A rninimum 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 SAYo passing the No. 4 sieve and less than2Yo passing the No. 200 sieve.
All filImaterials for support of floor slabs should be compacted to at least 95olo of maximum
standard Proctor density at a moisture content near optimum. Required fiIl should corsist of
imported granular soils devoid of vegetation, topsoil and oversized rock.
We recommend vapor retarders conform to at least the minimum requirements of ASTM 81745
Class C material. Certain floor types are mol'e sensitive to water vapor transmission than others.
For floor slabs bearing on angular gravel or where flooring system sensitive to water vapor
transmission are utilized, we recommend a vapor barrier be utilized conforming to the minimum
requirements of ASTM 81745 Class A material. The vapor retarder should be installed in
accordance with the manufacturers' recommendations and ASTM E1643.
Underdrain System: Although fi'ee water was generally not encountered in the exploratory pits,
it has been +':r ev++rlense !n r:r+untain+r:s -3::eas +nd r.'rhere there ase e1=-;-' g*i!u th+.t !+*a! perched.
groundwater can develop during times of heavy precipitation or seasonal runoff (such as the
slight seepage at bottorn of the topsoil at Pit l). Frozen ground during spring tunoff can create a
perched condition. We recommend below-grade construction, such as retaining walls,
+ra'-.vlspa*e s:ld bss.^meiit +isae, be pr+te+te4 9+e'se#i*g e"-d h3.'dr+str"tie plass-r:re build*p b3.
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 ievel of
excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum 1o/o to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than ZYo passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a
nraximum size of 2 inches. The drain gravel backfill should be at least 1% feet deep.
Surface Drainage: The following drainage precautions should be observed during eonstrustion
and maintained at all times after the residence has been compieted:
Kumar & Associates, lnc, @ Project No. 21-T-331
-4-
1)lnundation ofthe foundation excavations and underslab areas should be avoided
during construction. Drying could inorease the expansion potential of the clay
soils.
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 90% of the maximum standard Proctor density in landscape:Lreas.
Frcc-draining wall backfill should be covered with filter fabric and capped with
about 2 feet of the otr-site, finer graded soils t"o reduce surlace water infill-ralion.
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 stnrctures.
Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Landscaping which requires regular heavy irrigation, such as sod, should be
located at least 5 feet from the building.
3)
4)
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Qaa4in Qr;+*o'*' D*^file PitS 1 =::d 2 l+Cate<l u'if!rj-.-r f-1,.e i':r-c-:='rr:eeil e+nfir r!!qr:nq=! jar-44 elaF^'3'.tetoAL-La;.:L L.i ri:;;it .i iui;iL A ::- , ;iiu i .-!$.LJ 1i iiiiiii iii! ij:UFU;L'J arlijlil UiJFU;;; ;tL; ;tiLU;ji!:-;!u
moderately blocky clay with scattered gravel to the pit depths of 8 feet. The USDA gradation
testing results of the sample taken frorn Profile Pit 2, presented on Figure 6, indicate a soil type
of 2A (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 atthis time. We make no waranty either
express or irnplied. The conclusions and recornmendations 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 shown on Figure 2, the proposed rype 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 fliture. If the client is concerned
about MOBC, then a professional in this special field of practice should be consulted. Our
findings include interpolation and exfiapolation 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 during constmction appear different from
those described in this report, we should be notified at once so re-evaluation of the
recommendations may be made.
2)
Kumar & Associates, lnc. o Project No.2l-7-331
-5-
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 dwing construction to review and
mcnitor ihe impiementation of our recommendations, and to verifu that the recommendations
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 geotecirnicai engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respectfuily Submitted,
f{uriar,+:n {k ;Lgs,*E:$* g*s. E.rxc"
Steven L. Pawlak, P.
Reviewed by:
..
Daniel E. Hardin, P.E.
SLP/kac
Attachments: Figure I - Location of Exploratory Pits
Figure 2 * Logs of Exploratory Pits
Figures 3 and 4 - Swell-Consolidation Test Results
Figure 5 - Cradation Test Results
Figure 6 * USDA Gradation Test Results
Table 1 - Summary of Laboratory Test Results
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PIT 1
EL. 8200'
PIT 2
EL- 8204'
PP* 1
EL. 8195'
PP_2
EL. 8190'
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WC=32.8
DD=80 - GRAVEL=1 1
I SAND=14- stLT=sl 5
CLAY=24
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5 WC= 1 8.3
DD= 1 05 WC=.57.6
DD=67
+4=2Q
-2OO=73
10 10
LEGEND
TOPSOIL; ORGANIC SANDY SILT AND CLAY, MOIST TO VERY MOIST, DARK BROWN, SCATTERED
BASALT ROCKS.
CLAY (CL); SILTY, SANDY, SCATTERED GRAVEL AND COBBLES, STIFF, VERY MOIST TO
SLIGHTLY MOIsT, BROWN, MEDIUM PLASTIEITY, MODERATELY BLOEKY.
I .3 CNIVTL AND CLAY (GC-CL); SANDY, COBBLES, SCATTERED BOULDERS, MEDIUM DENSE/VERY
K:.})sttrr, MolsT, BRowN, BASALT ROCK.
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HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE.
DISTURBED BULK SAMPLE.
NOTES
i. THi TXPLG*ATGftY FiT3 ''*'€RE EXCAYAT;D'fv'iTH A EACKij=$t Cii #AY i+,:,C?i.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
THE EXISTING CABIN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL AND REFER TO
PIT 1 AS ELEVATION 8200" ASSUMED.
4. THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY
TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETIVEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL ryPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. SLIGHT
srgp.a.c5 Et!c+uf.lT595t .a.T 3 f55T !|,1 PlT 1_ PITS 9595 eAC!1F!LL9D S+-qS5+U5!.lT T+
SAMPLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (PCT) (ASTU D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ISTU O +ZZ);
-?OO= PERCENTAGF PASSING NO" 2OO SIEVE TASTM D 1140);
GRAVEL = PERCENT RETAINED ON NO. 10 SIEVE;
SAND = PERCENT PASSING NO. 10 SIEVE AND RETAINED ON NO. 525 SIEVE;
SILT = PERCENT PASSING No. 525 SIEVE TO PARTICLE SIZE .002MM;
CLAY = PERCENT SMALLER THAN PARTICLE SIZE .002MM.
21-7-331 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
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SAMPLE OF: Sondy Cloy
FROMrPit1O5.5'
WG = 18.5 %, DD = 105 pcf
-2O0 = 73 %
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EXPANSION UNDER CONSTANT
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APPUED PRESSURE - KSF 10 100
21 -7 -331 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3
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EXFANSiAI.i UNDEft EONSTANi
PRESSURE UPON WETTING
SAMPLE OFr Cloy
FROM:Pll 2@7'
WC = 37.6 %, DD = 67 pcf
D-ffHlllt
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
';l:,
'I
1.0 100
21 -7 -331 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 4
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HYDROMETER ANALYSIS SIEVE ANALYSIS
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50
50
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30
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70
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OF INM
CLAY TO SILT COBBLES
uiiAvLL it ,n
LIQUID LIMIT
SAMPLE OF: Cloy wllh Grovel
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PI.ASTICITY INDEX
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oocordonoo wlth ASIU 06913, ASIII D7928,
ASTII Cl50 ondfu lsm Dll.to.
SAND GRAVEL
COAPSFFINEMEDIUM FINE COARSE
21 -7 -331 Kumar & Associates GRADATION TEST RESULTS Fig. 5
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Geotechnica and Materials Engine rrs
and Environrlental Sc entists
TAI|ILE 1
SUMMARY OF LABORIATORY TEST RESULTS
SOIL WPE
Sandy Clay
Clay viiith Gravel
Clay
Clay
Silt Lcam
EI-AY
$t
24
SILT
t%t
15
t%t
SAND
14
USDA SOIi. TEXTURE
$t
GRAVI|L
11
{%)
slLr&cLAY
73
SAND
t%)
7
GRADATION
t%l
GRAVEL
20
NATUFIAL
DR\"
DENSIIY
(pctl
10Jr;
80
67
}iIATURAL
II{OISTURE
(ONTENT
vt
18.3
32.8
37,6
DEPTH
(fi)
5%
8-9
4
7
+5
SAIIPLE LOCATpN
PIT
I
2
Profile
Pit
2
lilo.2l-7-331