HomeMy WebLinkAboutSubsoil Study for Foundation Design 04.22.2021lGrtiffii,hmfmåi';-*5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@Jcumarusa.com
www.kumarusa.com
^n
Emdoyac owËd coraponf
Ofüce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
April22,202l
Domoplex, LLC
Attn: Slawek Wojciuch
2550 Highway 82, Unit l08A
Glenwood Springs, Colorado 81601
slawek@dp-mollex,çqm
Project No. 21-7-215
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 66, Filing 5,
Elk Springs, 0039 Crescent Place, 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 Domoplex, LLC dated February 1I,2021. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: Design plans were in progress at the time of our study. The proposed
residence will generally be one to two stories of wood frame construction over a crawlspace or
walkout basement and located as shown on Figure 1. The basement and attached garage floors
will be slab-on-grade. Cut depths are expected to range between about 2 to 8 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, grass and juniper trees at
the time of our site visit. The topography of the building area is moderately sloping down to the
south at a gtade of around l0%o with about 8 feet of elevation difference across the building
footprint. Snow cover was patchy and basalt cobbles were exposed on the ground surface of the
lot.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits at the approximate locations shown on Figure I and before the building footprint
plan was provided. The logs of the pits are presented on Figure 2. The subsoils encountered,
below about I to 2 feet of topsoil, consist of very stiff to hard, highly calcareous sandy silt with
basolt grovel to a depth of7 to TVzfcct ovcrlying basalt gavcl and cohblcs in a calcareous sandy
silt matrix to the excavated depths of I to 9Yz feet. Results of swell-consolidation testing
performed on a relatively undisturbed sample of the upper silt, presented on Figure 3, indicate
low compressibility under light loading with low collapse potential (settlement under constant
load) when wetted and moderate compressibility under additional loading after wetting. Results
of gradation analysis performed on a sample of the silt and gravel (minus 3-inch fraction) are
shown on Figure 4. 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 silt soils with basalt rocks, below the upper topsoil or clay
soils, designed for an allowable soil bearing pressure ot-l-&Q_pgllor support of the proposed
residence. Initial settlements are expected to be minor, less than I inch with additional
differential post-construction settlement of around 1 inch if the bearing soils are wetted.
Footings should be a minimum width of 18 inchcs for continuous walls and2 fcct 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 silt and rock
soils. We should observe the completed excavation for bearing conditions prior to forming
footings. Exterior footings should be provided with adequate cover above their bearing
elevations for frost protection. Placement of footings at least!6 inchegbelow 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 fragments larger than 6 inches.
Floor Siabs: The natural on-site soiis, exclusive of topsoii, are suitabie to support iightly loadeci
slab-on-grade construction. Slab subgrade can be re-established with suitable onsite soils or
imported 3/o-inch road base sandy gravel. 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 clesigner based on experience ancl the intencled slab nse. 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 50Yo passing the No. 4
sieve and less than 2o/o passing the No. 200 sieve.
Kumar & Associates, lnc. @ Project No. 21.7-215
-3-
All fill materials for support of floor slabs should be compacted to at least 95%o of maxlmum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
onsite soil or imported granular 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 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,
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 minimum lYoto
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2o/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 llzfeet 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 95%o af the maximum standard Proctor density 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
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 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 inigation 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.
Kumar & Associates, lnc. @ Project No. 21-7-215
-4-
Limitntions: This study has been eonducted in aceordanee with generally aceepted geotechnieal
engineer{ng principles and praetices in this area at this time. We make no wzu:ranty either
oxpress or irnplied. The eonclusions and reçommendations 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 ffie of construetion, and our exper{ence in
the area. Our services do not include determining the presence, prevention or possibility of mold
or othçr biological conta¡ninants (MOEC) developing in the future. If the client is concçrned
about MOBC, then a professionai in this special field of practice should be cÕnsulted" Our
findings include inteqpolation and extrapolation of the subsurface conditions identified at the
exploratory pits and variations in the subsurface conditions rnay nat beeome evident until
exeavation is performed. If conditions encountered during constnietion 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 trse by our elient for design purposcs" 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 implernentation of our recommendations, and to verify that the reçomrnendations
havc been appropriately interpreted. Significant design changes may require additional analysis
or rnodifications to the recommendations presented herein. 'We recornmcnd on-site observation
of excavations and foundation bearing strata and testing of structural fill by a representative of
the geotechnieal engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respeotfully Submitted,
Kurcãs!: &. AssoeÈates,
Steven L. Pawlak, F
Reviewed
!
Daniel E. Hardin, P.E.
SLF/kas
Attachments: Figure I - Location of Exploratory Fits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Swell-Consolidation Test Results
Figure 4 - Gradation Test Results
Table I - Surnmary of,taboratory Test Results
Kr¡nmar Sr,AtsosiaÊcç, lnc" @ Frojecå i{c. ä"l"f-ff$
CR CENT LANE
CRESCENT
PLACE
PlT 1
LOT 66, FILING 5
APPROXIMATE SCALE-FEET
15 0
21 -7 -215 Kumar & Assoeiates LOCATION OF EXPLORATORY PITS Fig. 1
ü
s
,
s
PIT 1 Ptl 2
0 0
ÞtJ
LÀl
LL
I-F
û_
tiJ
Él
, Wü= 1 2.3
I +4=62
WC=9.1
DD=90
-200=84
t--tJ
L¡J
L!
IIl--
o_
UJô
5 t
I -200= 1 0
LL=4 1
Pl=4 -
10
LEGEND
10
TOPSOIL; ORGANIC SANDY SILT, BROWN
V()
w
CALCAREOUS S|LT AND GRAVEL (ML-SM); SANDY, GRAVELLY, HARD, SLIGHTLY MOIST, PALE
TAN, BASALT ROCK.
GRAVEL AND SILT MATRIX (CU-UI); COBBLES, SANDY, DENSE, SLIGHTLY MOIST, PALE TAN,
BASALT ROCK.
F
t
HAND DRIVEN 2-INCH DIÄMETER LINER SAMPTE
DISTURBED BULK SAMPLE.
I PRACTICAL DIGGING REFUSAL.
NOTES
1. THE EXPLORATORY PIIS WERE EXCAVATED WITH A BACKHOE ON MARCH 9,2421
2, THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY TAPING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. 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 DEGREEn\/ Ît rr r/rÎt r^ñ r rôrñIMTLIÈU Þ I INtr Mf INUU UJLU.
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 THË TIME OF EXCAVATION. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULÏS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
-2oO= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1 1a0);
LL = LIQUID LIMIT (ASTM D a318)¡
Pl = PLASTICITY INDEX (ASTM D 4318).
21 -7 -215 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
g
frå
)
SAMPLE OF: Colccreous Scndy Cloyey Sìlt
FROM:Pit2@3.5'
WC = 9.1 %, DD = 90 pcf
-20O = 84 %,
ADDITIONAL COMPRESSION
UNDËR CONSTANT PRESSURE
DUE TO WETTING
\
Tho
in
D-S46.
1
0
àç
J)
l"rl
=(n
I
z.ot-
ô
=o
U)zo(J
-1
2
-3
4
5
-6
-7
-8
1.0 APPLIED PRESSURE - KSF t0 100
21 -7 -21 5 Kumar & Associates SWËLL_CONSOLIDATION ÏEST RESULTS Fig. 3
&
HYDROMETER ANALYSIS SIEVE ANALYSIS
TIME REAOINÈs
2¿ HRS 7 HRS
u.s. staNnÄxo sEflEs OLEAR SOUARÈ ÕPLNINöS
alA¡ ?lt' 1 t/a'
i i----i ,/
-....i--.. , F^ -ii
. .r ¡...- ---f-i -
, -.-_.i ,i --- -- -1 --+-- - - -
''' '' r''i _
- ---i-i-
t-::::l:l-!:"'......i1..itl ,,L
ri
'' '-l ' rl -
...t.;
-i--f-- ----................¡....t.... .
lt j j i t -( ii ,lii rl
.'!i
{a
f
160
30
¡o
70
60
50
¿ö
30
20
1ô
0
n
10
30
40
50
€o
70
ao
90
?
Ë
100¡ .600
.425
l.f 8
152
DIAMET IN RS
CLAY TO SILT COBBLES
GRAVEL 62 % SANO 2A %
LIQUID LIMIT - PLASTICITY INDEX
SAMPLE OF: Sondy Sill ond Bosolt Grovel
SILÏ AND CLAY 'IO %
FROM:Plt1@4.5'-6
Thrs€ læl rosulls qÞply only lô lhe
tomplsa whlch sólê l€sl6d. Ihêlô.iîhg reporl 3holl ñôt b6 reproducod,
.xe€pl in full, wllhoul lh6 wrlllÊn
ôpprovôl ol Kuñôl & As¡ôclolos, lnc.
Slêv6 dnolysls togllng ls pqrlorm€d ln
occordonce wlrh ASTM 06913, ASÍM D7S28,
ASTM C136 ond/or ASTM Dl140.
SAND GRAVEL
FINE MEDIUM COARSE FINE COARSE
21 -7 -215 Kumar & Associates GRADATION TEST RTSULTS Fig. 4
lcrtpggggffiä.-"TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo. 21-7-215Calcareous Sandy ClayeysiltSOIL TYPESandy Silt and BasaltGravel(psllUNCONFINEDCOMPRESSIVESTRENGTHPLASTICINDEXIololATTERBERG LIMITS(o/olLIQUID LIMIT84PERCËNTPASSING NO.200 stEVE%tSANDGRADATION(%)GRAVEL90locflNATURALDRYDENSTTY9.tt%tNATURALMOISTURECONTENT3%fftìDEPTH4I1012.34Yr-642862I2SAMPLE LOCATIONPIT