HomeMy WebLinkAboutSubsoil Study for Foundation Design 08.12.2021KtnËffiilT#i!1i'ffi*å'Ygd'*'.
-
5020 County Road 154
Glenrvood Springs, CO 81601
phone: (970) 945-'7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www.kurnarusa.comAn lmployrr Owñrd Compony
Ofüce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
August l2,2o2l RECEIVEI)
DM Neuman Construction $EP ZT '¿ß2|r
Attn: Jason Neuman
P.o. Box 2317 f.îni,iFiPrrt?#il#
Glenwood Springs, Colorado 81602
imn@dmneuman.com
Project No. 2l-7-568
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 10, Filing 8,
Elk Springs, Elk Springs Drive, Garfield County, Colorado
Gentlemen:
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 DM Neuman Construction dated June 28, 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 one to two stories of wood frame
construction over a crawlspace with an attached slab-on-grade garage located in the building
envelope shown on Figure 1. Cut depths are expected to range between about 3 to 7 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 site was vacant and vegetated with sagebrush and grass at the time of our
site visit. The topography of the building area is a hillside with a moderate slope down to the
southwest at a grade of around 5 to l0%o, with a broad swale along the eastern part of building
envelope. There is approximately 9 feet of elevation change across the building envelope
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
three exploratory pits at the approximate locations shown on Figure l. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about 1 foot of topsoil and 2 to 4 feet of
stiff to hard sandy silty clay, consist of hard, highly calcareous sandy silt with basalt gravel,
cobbles and boulders. Results of swell-consolidation testing conducted on relatively undisturbed
liner samples of the clay soils, shown on Figures 3 and 4, indicate low compressibility under
existing low moisture conditions and light loading and a low expansion or moderate collapse
.ì
-L-
potential when wetted under load. Results of gradation analysis performed on a sample of the
silty sandy gravel (minus 3-inch fraction) are shown on Figure 5. The laboratory test results are
summarized in Table l. No free water was observed in the pits at the time of excavation and the
soils were slightly moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
placed on the undisturbed natural calcareous silt with basalt rocks, below the upper topsoil and
clay soils, designed for an allowable soil bearing pressure of 2.000 pslfor support of the
proposed residence. Sefflements are expected to be minor, less than I inch. Footings should be a
minimum width of 16 inches for continuous walls and 2 feet for columns. Loose disturbed soils
encountered at the foundation bearing level within the excavation should be removed and the
footing bearing level exl.cntlecl tlown to the undisturbed natural rocþ soils. We should observe
the completed excavation for bearing conditions prior to forming footings. Exterior footings
should be provided with adcquate 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.
Continuousfoundation*utt,ffiinforcedtopandbottomtospanlocalanomaliessuch
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 thc on-site soil as backfill excluding organics and rock fragments
larger than 6 inches.
Floor Slabs: The natural on'site soils, exclusive of topsoil, are suitable to support lightly loaded
slab-on-grade construction with a risk of settlement or heave if the clay soils are wetted. In sub-
excavated areas, the slab subgrade can be re-established with suitable onsite soils or imported
3/¿-inch road base sand and gravel. To reduce the effects of some differential movement, non-
structural floor slabs should bc separated fi'om all bcaring walls and colunurs with cxpansiun
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 slabs for suppt-rrt. This mal.erial should consist of minus 2-inch aggregate with
less than 50% passing 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 leastg1Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
onsite predominantly granular soil or imported granular soils devoid ofvegetation, topsoil and
oversized rock.
Kumar & Associates, lnc. o Project No. 21-7-568
-3-
Underdrain System: Although free water was not encountered during our exploration, it has
been our experience in the areathat local perched groundwater can develop during times of
heavy precipitation or seasonal runoff. Frozen ground during spring runoffcan also create a
perched condition. We recommend below-grade construction, such as retaining walls and
crawlspace 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 minimum lYoto
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2%o 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 lYzfeet deep.
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.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95Vo of the maximum standard Proctor density in pavement and slab areas
and to at least 90Yo 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.
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 l0 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in pavement and walkway areas. A swale should be
provided uphill to direct surface runoff around the residence.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irigation should be located at least
l0 feet from the building. Consideration should be given to the use of xeriscape
to limit potential wetting of soils below the foundation caused by irigation.
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
Kumar & Associates, lnc. @ Project No. 21.7.568
4
and to the dspfbt ¡hown ou Flgure 2, the propoæd fypo of oonstrueúioa, and orn exper{cnoc in
the waa, ûlr ¡eryie¿c do not inaMo dotonnining tho preroueo, prwætiolr or pomibllity of mold
or othø biologieel emtsnninants (McFq developlng ln the fufire, lf the client í¡ eonaennod
about MCIBe, thsn eprofonional in thi¡ ryeelal field ofpaetice ¡houldbe ssnrulted, O¡r
findings include interyoletion ald cr$ryolatlon ofthe ¡ubn¡dasë c¿nditlone tddlfied st ths
apluatory plts aad vat{atíonc in the n¡bn¡rfaae conditisn¡ may not beeoure wialeût wül
qsevstion is pøfomsd, If ssnditions encountqed during soncEucdotr apperdífføæt ûrm
those d€s€ríbed in this rgrert, we ¡hould b€ notíffed d ones so rewaluatÍon of tho
rcsommcndations may be oada
Thísrqorthasbeenpreþæedfortbeøclusiveuseþot¡rslicntfo¡designpr¡rlroûGs, tilçaæuot
rcryonsfUe fm tee.hical itrøprüdíono þ ottre'r of orn informetion. As lhc projcct wolveE we
shouldprovide surtifi¡€d cønlltstioni and ficld scrviccs drring gorisûrustion to rcviem, d
monitor tho ímplomentotíon of otr r€oormeûdationc, md to veríS th¡t thc rccomeaddims
hn¡e boea rympdusly ¡r¡crpetø. $ígnífiomt dcsign cbanges may reçrire additional analyoic
ormdifioations to theræmend*ionspresentd h€rein. Weæcormrcnd on-sito obsenntion
of excavations and fomdationbøing sffia and testing of sEr¡c'tüal filt by arepresentdive of
the geotec,hnical engin€€r,
If you have any çlestions or if we may bç of finther assistarce, pleaæ let us know.
Resp€etfr¡lty Submiüo{
Kumar & Associates, Inc.
David A Notóoom, Staff F"ngrnø
Reviewedb¡t
Steven L. Pawlak,
SLP/kac
Attachncnts:
Figrre2 Pits
Figwes 3 u¡d 4 - Swell{onsolidation Test Rcsults
Figtre 5 - Gr¡dation T6t Rcsults
Table I - Srmmry oflaboraûory Test Results
Pits
1gãa2
Kumar & Associa{es, lnc. s Project No. 21-7-568
tlll-l-lvJs llvntxouddvIìIIIIi?¡ìII:-'|¿cNntJ '0t rolt'.9Udì.Iild'-\*899-L- tZsalercossv ? Jetunyslrd ^uoIVUoldxr r0 N0tlvcotI '6U
E
Ë
PIT 1
EL. 6904'
PIT 2
EL. 6903'
PIT 5
EL. 6908'
0 0
WC=6.2
DD= 1 03 WC=6.1
DD=85!-l¡l
l¡JtL
I-t-(L
l¡Jo
q I
+4=32
-20O=2O 5
F
l¡JulIr
I-F(L
t¡Jo
t0 10
LEGEND
TOPSOIL; SANDY CLAY AND SILT, ROOTS AND ORGANICS, FIRM, SLIGHTLY MOIST, BROWN.
CLAY (CL); SANDY, SILTY, STIFF TO HARD, SLIGHTLY MOIST, TAN AND BROWN, SLIGHTLY
CALCAREOUS.
GRAVEL AND SrLT (GM-ML);
HIGHLY CALCAREOUS SANDY
CALCAREOUS.
BASALT GRAVEL, COBBLES AND PROBABLE BOULDERS IN A
SILT MATRIX, DENSE, SLIGHTLY MOIST, PALE TAN TO WHITE,
F
t
HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE.
I
I
J
I
DISTURBED BULK SAMPLE.
PRACTICAL DIGGING REFUSAL.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JULY 7,2021.
2. ÏHE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN 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 (PCT) (ASTV D 2216);+4 = PERCENTAGE RETAINED ON No. 4 SIEVE (ASTM D 422)¡
-2oo= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
^\-^u
o-' t/. ./:
. r{-
21 -7 -568 Kumar & Associates LOGS OF IXPLORATORY PITS tig. 2
E
n
SAMPLE OF: Silty Sondy Cloy
FROM: Pit 1 @ 1'
WC = 6.2 %, DD = 103 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
t
\
Ihæ b6t rô.ulb opply onv to bô
rcmpb8 tdd. ftâ b.üñg r.pod
¡kll not bâ Êprcducôd, oxcopt in
full, üúout bê rñtr€n opryl of(uNr ond þsæ¡otæ, lnc. Srêll
bnsollddlof, t Btiôg flomd ln
dcøddnc. s$ m D-4548.
1
àq
JJ
L¡J
=at1
I
zo
t-
ô
=ovlz.oo
0
-1
-¿
-3
-4
1.0 10 100
21 -7 -568 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 3
E
n
I
SAMPLE OF: Sllty Sondy Cloy
FROM:Pit3@ 2'
WC = 6.1 %, DD = 85 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
(
()\\
iñ
ônd
2
0
J-Z
l.¡J
=an
t-4
zotr
ô¡-oov)zo()_g
-10
-12
.l PRESSURE - KSF 10 t00
21 -7-568 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
HYDROMEÌÊR ANALYSIS SIEVE ANALYSIS
24 HRS 7 HRSa5 vlN 15 ltf, 60!tN
ÍIXE READI{GS
I'MIN al oo
U.S. STANDARO SERIES
450 a¡o 430 ¡16 t
CLUR SOUARE OPENINGS
3/A' 3/1" I 1/aâ
2û
100
90
go
70
60
50
40
30
20
10
o
to
20
30
40
30
60
70
ao
e0
100
v¡
OF IN MILLIMETERS
CLAY TO SILT COBBLES
GRAVEL 32 % SAND ¡f8 %
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Colcoreous Sllty Sondy Grovel
SILT AND CLAY 20 %
FROM:Pll1O4'-5'
Th.sc lo3l r.rulls opply only lo lh.romÞlc¡ whlch y6ro l.¡l.d. Tholc.l¡ñg r.porl lholl nol b. rôÞroducrd,.rcapl ln full, wlthoul lh. wrltt.n
opprovql of Kumo. ¡l Alroclolct, lnq.Sl.v. onolysls l.3llng ls pôrfomad ln
occo¡donc. wlth ASTM 06913, ÀSTM D7928,
ASTM Cl36 ondlor ASTM Dll¡10.
SAND GRAVEL
FINE MEDTUM lcOrnse FINE COARSE
21 -7 -568 Kumar & Associates GRADATION TTST RESULTS Fig. 5
K-JtffiHHzu=#
*2'
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
sÀilÞt F I ncaltfil{ton AfiERBERG LI[IITS
SOIL TYPE
SAI{D
(%)
PERCEIIT
PASSING NO.
200 SIEVE
LlaulD LlfrllT
t%t g"\
PLASTIC
iltDEX
l¡¡ll
ul{coflnilED
corPREsstvE
SIREI{GTHPII
Itfl
DEPTH
t%ì
]{AIURAT
t0tsfuRE
CONTEI{T
aDcfl
NATURAL
DRY
DEI{SITY
GRAVET
(%)
Silty Sandy ClayI6.2 t03I
48 20 Calcareous Silty Sandy
Gravel4-5 32
Silty Sandy ClayJ26.1 85