HomeMy WebLinkAboutSubsoil Studyl(+rtffi,ffirff'å'*"
An ßmployca Oq^tnad Go*npqny
502S County Road 154
ûlenwood Springs, CO 81601
phone: (970) 945-?9BB
fax: (970) 945-8454
email: kagl enwood@kumarusa.com
u':Nw.kumarusa.coct
Qffice l¡catioru: Denver (t{Q}, Parker, Colorado Springs, Fort Collinç, Glenrvood Springs, and Summit County, Colo¡ado
February 15,2021
Trish Cerise
16724 Highway 82
Carbondale, Colorado 8l 623
tuqhceri selô $n-ail. com
Project No.2l-7-138.3
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 3, Cerise Minor
Subdivision, North of 1,6724 Highway 82, Garfield County, Colorado
Dear Trish:
As requested, Kumar & Associates, lnc. performed a subsoil study for foundation design at the
subject site. The study was conducted in accordance with our agreement for geotechnical
engineering services to you dated January 18,2021. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report. Evaluation of potential geologic hazard impacts on the site is beyond
the scope of this study.
Proposed Construction: The proposed residence will be located in the area of Pit 1 on the site
as shown on Figure 1. Ground floors are proposed to be structural over a crawlspace or slab-on-
grade. Cut depths are expected to range between about 2 to 4 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 lot is relatively flat with a slight slope down to the south. Vegetation
consists of grass and weeds. There was about 2 to 3 inches of snow on the site at the time of our
site visit on January 20,2021.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating an
exploratory pit in the building arca at the approximate location shown on Figure 1. The log of
the pit is presented on Figure 2. The subsoils encountered, below about 1 foot of topsoil, consist
of ZtA feet of medium stift sandy silty cloy overlying relatively denso, slightly silty sondy gravel
with cobbles and small boulders down to the excavated pit depth of 5 feet. Results of a swell-
consolidation test performed on a relatively undisturbed sample of the sandy silty clay, presented
-2-
on Figure 3, indicate low compressibility under existing moisture conditions and light to
moderate loading. No free water was observed in the pit at the time of excavation and the soils
were moist.
Foundation RecommendatÍons: Consiclering the subsoil conditions encountered in the
exploratory pit and the nature of the proposed construction, rile recommend spread footings
placed on the undisturbed natural soil designed for an allowable soil bearing pressure of
2,000 psf for support of the proposed residence. The clay soils tend to compress under loading
and there could be some post-construction foundation settlement. Footings beadng on the gravel
soils should have a low settlement potential. Footings should be a minimum width of 18 inches
for continuous walls and2 feet for columns. Loose and 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. We should observe the completed foundation
excavation to confirm suitable bearing conditions. 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 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 larger than
6 inches.
tr'loor 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 diflerential movement, floor slabs
should be separated from all bearing walls and columns with expansion joints which allow
unrestrained vertical movsment. Floor slab conhol joints should be used to reduce damage due
to shrinkage cracking. The requirements for joint spacing and slab reinforcement should be
established by the designerbased 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 50% passing the No. 4
sieve and less than 2% passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at leastglo/a ofmaximum
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
Kumar & Associates, lnc. @ Project No.21.7.138.3
,3-
heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched
condition. 'We recornmend below-grade construction, such as retaining walls, deep crawlspace
and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain
system. Shallow crawlspaces (less than 4 feet) and slab-on-grade floors near exterior grade
should not need an underdrain.
If installed, 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 ofexcavation and at least I foot below lowest adjacent finish grade and
sloped at a minirnum lo/oto a suitable gravity outlet or sump and pump. Free-draining granular
material used in the underdrain system should contain less than 2% 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 llz feet 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 of the 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 90% of the maximum standard Proctor densþ in landscape areas.
Free-draining wall backfill should be 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 10 feet in unpaved areas and a minimum slope of
3 inches in the first 10 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
express or implied. The conclusions and recommendations submitted in this report are based
upon the data obtained from the exploratory pit excavated at the location indicated on Figure 1,
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
Kumar & Assoeiates, lnc. 6 Project No.21.7.138.3
4
this special field of practice should be consulted. Our findings include interpolation and
extrapolation of the subsurface conditions identified at the exploratory pit 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. lVe are not
responsible for technical interpretations by others of our information. As the project evolves, we
should provide continued consultation ond field services during construction to roview and
monitor the implementation of our recornmendationso and to veriff that the recommendations
have been appropriately interpreted. Significant desigri 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 rnay be of furdrer assistance, please let us know.
Respectfu lly Submitted,
Kumar & Assocíateso Inc.
Daniel E. Hardin,
Rev. by: SLP
DEH/kac
attachments Figure 1 - Location of Exploratory Pit
Figure 2 -Logof Exploratory Pit
Figure 3 - Swell-Consolidation Test Results
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Kumar & Associatee, lnc. o Project No.21-7.138.3
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PIT I
LOT 3
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LOT 2
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LOT 1
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APPROXIMATE SCALE-FEET
21-7-138.3 Kumar & Associates LOCATION OF EXPLORATORY PIT Fig. 1
PIT 1
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DD=97
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LEGEND
TOPSOIL; SLIGHTLY SANDY CLAY, ROOTS AND ORGANICS, MEDIUM STIFF, MOIST, DARK
BROWN.
CLAY (CL); SANDY, WITH SCATTERED ROUNDED COBBLES, MEDIUM STIFF TO STIFF, MOIST,
BROWN AND DARK BROWN. USDA CLASSIFICATION SILTY CLAY LOAM.
GRAVEL (GV); S¡NOY, SILTY, WITH COBBLES AND SMALL BOULDERS, DENSE,
AND BROWN. ROCKS ROUNDED IN SHAPE. USDA CLASSIFICATION EXTREMELY
MOIST, GRAY
GRAVELLY SAND.
F HAND DRIVEN LINER SAMPLE
NOTES
1. THE EXPLORATORY PIT WAS EXCAVATED WITH A BACKHOE ON JANUARY 20, 2021.
2. THE LOCATION OF THE EXPLORATORY PIT WAS MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
5. THE ELEVATION OF THE EXPLORATORY PIT WAS NOT MEASURED AND THE LOG OF THE
EXPLORATORY PIT IS PLOTTED TO DEPTH.
4. THE EXPLORATORY PIT LOCATION SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE
IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOG REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PIT AT THE TIME OF EXCAVATION. PIT WAS
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216).
-¡
I
?21-7-138.3 Kumar & Associates LOG OF EXPLORATORY PIT Fig. 2
SAMPLE OF: Sondy Silty Cloy
FROM:Pit1e^2'
WC = 18.3 %, DD = 97 pcf
NO MOVEMENT UPON
WETTING
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21-7 - 138.5 Kumar & Associates SWELL-CONSOLIDATION TEST RTSULTS Fig. 3