HomeMy WebLinkAboutSubsoils Reportl(lAfliffifi'.ffifffi*ii,"i*"'
An Emfloycc otflncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970)945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
wwwkumarusa.com
Office lncations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
February 27,2025
Tom Lester
P.O.Box2329
Basalt, Colorado 81621
toml@ lesterdevelopment. com
Project No. 25-7- I 62.06
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot6, Whitecloud
Ridge, 500 Whitecloud Road, Garfield County, Colorado
Dear Tom:
As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations
at the subject site. The study was conducted in general accordance with our agreement for
geotechnical engineering services to you dated February 25,2025. 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
field exploration. The proposed residence is assumed to be a two-story residence with an
attached garage located on the site in the general area of the pits shown on Figure 1. Ground
floors are assumed to be structural over crawlspace for living areas and slab-on-grade for the
garage. Cut depths are expected to range between about 2to 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 described
above, we should be notified to re-evaluate the recommendations presented in this report.
Site Conditions: The subject site was vacant at the time of our field exploration. There was
patchy snow cover. The ground surface was gently sloping down to the southwest at a grade
estimated at about 5 percent. Vegetation consists of grass and sagebrush in the building arcaand
juniper trees to the south of the building area. There were basalt boulders and cobbles exposed
on the ground surface in the juniper trees.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
two exploratory pits at the approximate locations shown on Figure l. The logs of the pits are
presented on Figrne 2. The subsoils encountered, below about 1 foot of topsoil, consist of 5%
to 6 feet of silt and sand overlying dense, basalt gravel and cobbles in a calcareous sandy silt
a
matrix. Results of swell-consolidation testing performed on relatively undisturbed samples of
sand and silt, presented on Figure 3, indicate low to moderate compressibility under conditions
of loading and wetting. No free water was observed in the pits at the time of excavation and the
soils were slightly moist to 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 soil designed for an allowable soil bearing pressure of
2,000 psf for support of the proposed residence. The soils tend to compress after wetting
and there could be some post-construction foundation settlement. Footings should be a
minimum width of 18 inches for continuous walls and2 feet 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 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 well 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 alateral earth pressure based on an equivalent
fluid unit weight of at least 50 pcf for the on-site soil as backfill.
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 diflerential 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 designer based on experience and the intended slab use. A minimum 4-inch
layer of relatively well graded sand and gravel should be placed beneath slabs-on-grade for
support. This material should consist of minus 2-inch aggregate with less than 50% passing
the No. 4 sieve and less thanl2o/o passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at Ieast95%o 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 areathat local perched groundwater can develop during times of
heavy precipitation or seasonal runoff. Frozen ground during spring runoffcan create aperched
condition. We recommend below-grade construction, such as retaining walls, crawlspace areas
deeper than about 4 feet and basement areas, be protected from wetting and hydrostatic pressure
buildup by an underdrain system. The assumed shallow crawlspace area does not require a
foundation drain.
Kumar & Associates, lnc. o Project No. 25-7-162.06
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If installed, 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 at each level of excavation and at least I foot below lowest adjacent finish
grade and sloped at a minimum Vzo/oto a suitable gravrty outlet, drywell or sump and pump
system. Free-draining granular material used in the underdrain system should contain less than
2Yopassngthe 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 and covered with filter
fabric such as Mirafi l40N or 160N.
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 95Yo of the maximum standard Proctor density in pavement and slab areas
and to at least 90% 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 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 ureas.
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
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 inigation.
Limitations: This study has been conducted in accordance with generally acceped 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 pits excavated at the locations indicated on Figure 1
and to the depths shown on Figure 2,theproposed 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 concerned
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
Kumar & Associates, lnc. o Project No. 25-7-162.06
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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 ourrecommendations, and to verifu that the recofilmendations
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 Submiued,
Kumar & Associates, lnc.
James H. Parsons, P.E.
Reviewedby:
b
Daniel E. Hardin, P.E.
JHP/kac
attachments Figure 1 - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Swell-Consolidation Test Results
Table I - Summary of Laboratory Test Results
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Kumar & Associates, lnc. @ Project No. 25-7-162.06
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APPROXIMATE SCALE-FEET
25-7-162.06 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
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PIT 1
EL. 100'
Pt'l 2
EL. 101 .5'
o 0
WC=15.2
DD=1 O0
FlrllrlL-
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WC=9.0
-200=85
WC=10.2
DD=88
-200=68 5
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LEGEND
N
TOPSOIL; SILT, SANDY, ORGANICS, FIRM/FROZEN, MOIST, BROWN.
SAND AND SILT (SM-ML); CLAYEY, CALCAREOUS HARD, SLIGHTLY MOIST, PALE TAN.
W
GRAVEL AND COBBLES (GM); SMALL BOULDERS, BASALT ROCK, CALCAREOUS SANDY SILT
(cALlcHE) MATRtx, DENS,E SL|GHTLY Molsr, PALE TAN AND GRAY.
F
t
HAND DRIVE SAMPLE.
PRACTICAL REFUSAL TO THE BACKHOE DIGGING.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON FEBRUARY 25, 2025
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 1OO FT 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. T.ABORATORY TEST RESULTS:
wc = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (PCt) (ASTU D 2216);
-200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
25-7-162.06 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
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SAMPLE OF: Sondy Cloyey Silt
FROM:Pii1(|-2'
WC = 15.2 %, DD = 100 pcf
\
NO MOVEMENT UPON
WETTING
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- KSF
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SAMPLE OF: Sondy Cloyey Silt
FROM:Pit2e^3.5'
WC = 10.2 %, DD = E8 pcf
-2OO = 68 %
db.ulthrt nprldudd,tE rdtti $drlE
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ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
25-7-162.06 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3
l(tA l(urmr & Assciatesn lnc,@
Geotechnical and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Projec{ No. 25-7-1 62.06
SOIL TYPE
Sandy Clayey Silt
Sandy Clayey Silt
Sandy Clayey Silt
UNCONFINED
COMPRESSlvE
STRENGTH
{psfl
ATTERBERG LMNS
PLASTIC
INDEX
(olol
LIQUID LIMIT
lo/ol
PERCENT
PASSING NO
200 stEvE
83
68
GRADATION
SAND
(%)
GRAVEL
(%)
NATURAT
DRY
DENSITY
(ocfl
100
88
NATURAL
MOISTURE
CONTENT
lo/.1
15.2
9.0
1,0.2
DEPTH
{ft}
2
4
3Y,
PIT
1
2