HomeMy WebLinkAboutSubsoils Report for Foundation Designrcrf fliffihi'åifßtrn'"'Ëü*'*
5020 County Road 154
Glenwood Sptings, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www.kumarusa.comAn Employcc Ownad Compony
Offrce Locations: Denver (HQ), Parkeq Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
August 4,2023
James Gornick Building Specialists
Attn: Jim Gornick
1005 Cooper Avenue
Glenwood Springs, Colorado 81601
i eornick I 98 8@ gmail.com
Project No.23-7-407
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 1, River Ridge,
River Ridge Drive, Garfield County, Colorado
Dear Jim:
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 James Gornick Building Specialists dated July 6,2023. The data
obtained and our recommendations based on the proposed construction and subsurface
conditions encountered are presented in this report.
Proposed Construction: Plans for the proposed residence were conceptual at the time of our
study. The proposed residence will generally be a one- or two-story wood-frame structure with
attached garage and covered patio and detached unit located on the site approximately as shown
on Figure l. Ground floors could be slab-on-grade or structural over crawlspace. Cut depths are
expected to range between about 2 to 6 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 desuibed
above, we should be notified to re-evaluate the recommendations presented in this report.
Site Conditions: The subject site was vacant of structures and there was cut and fill grading for
the proposed residence at the time of our field exploration. The ground surface was relatively
flat and gently sloping in most of the building envelope then sloping down around 4 feet in
elevation in the southern part. Vegetation consists of grass and weeds with scattered scrub oak.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
four exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about I foot of topsoil, mainly consist
of dense, silty sandy gravel with cobbles down to the maximum explored depth of 5 feet. A
layer of clayey silty sand and gravel was encountered in Pit 4 from I to 3 feet deep. Results of
gradation analyses performed on samples of silty sandy gravel and cobbles and clayey silty
a-L-
gravelly sand (minus 3-inch fraction) obtained from the site are presented on Figure 3. 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 gravel soil designed for an allowable soil bearing pressure of
2$00 psf for support of the proposed residence. The upper silty clayey soils tend to compress
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after wetting and should be removed to limit post-construction foundation settlement. We should
observe the completed foundation excavation prior to placing footing forms. Structural fill
placed to reestablish design bearing level can consist of the onsite soils compacted to at least
98olo of standard Proctor density at near optimum moisture content. Footings should be a
minimum width of l6 inches for continuous walls and2 feet for columns. Topsoil, existing fill
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 gravel
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 reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least l0 feet. Foundation walls and
retaining structures which are laterally supported and can be expected to undergo only a slight
amount of deflection should be designed for a lateral earth pressure computed on the basis of an
equivalent fluid unit weight of at least 50 pcf for backfill consisting of the on-site granular soils.
Cantilevered retaining structures which are separate from the residence and can be expected to
deflect sufficiently to mobilize the full active earth pressure condition should be designed for a
lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 40 pcf
for backfill consisting of the on-site granular soils. Resistance to sliding at the bottoms of the
footings can be calculated based on a coefficient of friction of 0.45. Passive pressure of
compacted backfill against the sides of the footings can be calculated using an equivalent fluid
unit weight of 375 pcf. The coeffrcient of friction and passive pressure values recommended
above assume ultimate soil strength. Suitable factors of safety should be included in the design
to limit the strain which will occur at the ultimate strength, particularly in the case of passive
resistance.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded
slab-on-grade construction. 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
Lo slrrinkage r.:raukirrg. The requirelilÊltts for joint spaciug ancl slab rsinforcrcrlttcrnt shoulcl bc
established by the designer based on experience and the intended slab use. A minimum 4-inch
Kumar & Associates, lnc. o Project No. 23-7-407
J
layer of relatively well graded sand and gravel such as road base should be placed beneath slabs-
on-grade for support. This material should consist of minus 2-inch aggregate with less than 50Yo
passing the No. 4 sieve and less than I2%o 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 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
heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched
condition. We recommend below-grade construction, such as retaining walls and basement areas
(if any), be protected from wetting and hydrostatic pressure buildup by an underdrain system.
The drains should consist of rigid perforated PVC drainpipe placed in the bottom of the wall
backfill surrounded above the invert level with free-draining granular material. The drain should
be placed ateach level ofexcavation and at least I foot below lowest adjacent finish grade and
sloped at a minimumY'Yo to 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 1 Yz feet deep and covered with filter fabric.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the residence has been completed:
l) 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 95o/o of 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, 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 6 inches in the first l0 feet in unpaved areas and a minimum slope of
2Yzinches in the first l0 feet in pavement and walkway areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
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 waranty either
Kumar & Associates, lnc. @ Project No. 23-7-407
4
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 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 concemed
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 during 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 veriff 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 geotechnical engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
Kumar & Associates,
James H. Parsons,
Reviewed by:
#^,-/.
Steven L. Pawlak, P.E.
JHPlkac
attachments Figure 1 - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Gradation Test Results
Table I - Summary of Laboratory Test Results
Kumar & Associates, lnc, @ Project No. 23-7-407
PIT 2
PIT 1 --PlT 3
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APPROXIMATE SCALE-FEET
23-7 -407 Kumar & Associates LOCATION OF TXPLORATORY PITS Fig. 1
PIT 1
EL. I 00'
PIT 2
EL. 1 00'
PIT 3
EL. 1 00'
PIT 4
EL. 94,
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-200=33ì
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LEGEND
N TOPSOIL; SAND, SILTY, SCATTERED GRAVEL' ORGANICS' FIRM, SLIGHTLY MOIST' BROWN.
SAND AND GRAVEL (SC-OC); CLAYEY, SCATTERED COBBLES, SCATTERED ORGANICS, MEDIUM
DENSE, SLIGHTLY MOIST, BROWN.
TOPSOIL; SAND, SILTY, SCATTERED GRAVEL' ORGANICS, FIRM, SLIGHTLY MOIST' BROWN
L
L
DISTURBED BULK SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JULY 11,2023
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 MEASURED BY HAND LEVEL AND REFER TO
PIT 1 AS A lOO' ASSUMED BENCHMARK.
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 OONTENT (%) (ASTM D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (¡STV O ¿ZZ);
-2OO= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
WC=9.4
+4=62
-2OO=4
23-7 -407 Kumar & Associates LOGS OF EXPLORATORY PITS Fis. 2
ã
SIEVE ANALYSISHYDROMETER ANALYSIS
ÎII¡E RilDINCS
14 HRS 7 HRS
u.s- staNDAnD sEltËs
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nf
ã
&
H
r00
90
80
70
60
50
Æ
50
20
t0
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lo
20
30
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50
60
70
æ
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too
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.123
OF PARTICLES IN
t52
CLAY TO SILT COBBLES
GRAVEL 62 % SAND
LIQUID LIMIT
SAMPLE OF: Sllghtly Sllty Sondy Grovol
34%SILT AND CLAY 4 %
PLASTICITY INDEX
FROM: P¡t 2 O 2.5 ond 5' Comblnêd
2e
I
E
r00
to
80
70
80
50
ß
50
20
lo
o
0
to
20
¡0
10
50
t0
70
t0
eo
loo
?
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È
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t.18 I 2.53
2.OIN MILLIMETERS
l9 3a,t
DIAMETER OF
CLAY TO SILT COBBLES
GRAVEL 20 % SAND
LIQUID LIMIT
SAMPLE OF: Sllty Cloyey Grovelly Sond
17%
PI.ASTICITY INDEX
FROM:Pll 4.e2.5'
SILT AND CLAY 33 %
Th.tc lcll r.tullt opply only lo lh.
sompl.! whlch r.r. lcslad. Thr
l.¡llng reporl rholl nol br r.producrd,
cxcôpi ln full, wllhoul lhr vr¡tlcn
opprcvol ol Kumor & Arroclqt ¡, lñc,
Sl.v. onolysls lcs'llno lr Þartom.d ln
occordqncc wlth ASTM D6913, ASTM D7928,
AsTl¡ c156 ond/or ASTM Dtl,lo.
SAND GRAVEL
FINE MEDTUM ICOARSE FINE COARSE
HYDROMETER ANALYSIS SIEVE ANALYSIS
u.s.TIME RADINCS
2' HRS 7 HRS .,'
GRAVELSAND
MEDTUM lCOrnS¡FINE COARSEFINE
23-7 -407 Kumar & Associates GRADATION TEST RTSULTS Fig. 3
l(+llii"pi,ffip;ffii':'n;**'
-
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.23.7'107
ATI UMITSSÁMPIt ocaTtoN GRADATION
GRAVEL
("/"1
SAND
tkl
PERCENT
PASSING NO.
200 SIEVE
P/.\
LIQUID UMIT
t%ì
PLAS'IIC
INDEX
lDsfì
UNCONFINED
COMPRESSIVE
STRENGTH SOIL TYPEPIT
lfrì
DEPI}I
P/.1
NATURAL
MOISTURE
CONTENT
NATURAL
DRY
DENSIW
locfl
Slightly Silty Sandy Gravel6234422%&.5
Combined 9.4
47 JJ Silty Clayey Gravelly Sand42Y23.7 20