HomeMy WebLinkAboutSubsoil Studyrcrf iiffififfiiffin*;-"'5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
wwwkumatusa,comAn Employcc otrncd Co'mPonY
Office Locations: Denver (FlQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
May 4,2022 RECEIVED
Eddie Mumay
P. O. Box 551
New Castle, Colorado 81647
eddie (ã.oaci fi csh eetm eta I . net
it¡hi 1 3 2tì??
GARFIELD COUNTY
COMMUNITY DEVELOPMENT
Project No. 22-7 -227
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 13, The Rapids,
Rapids View Lane, Garfield County, Colorado
Dear Eddie:
As requested, Kumar & Associates performed a subsoil study for design of foundations at the
subject site. The data obtained and our recommendations based on the proposed construction
and subsurface conditions encountered are presented in this report. The study was conducted in
accordance with our agreement for geotechnical engineering services to you dated March 14,
2022.
Proposed Construction: The residence will be a two story wood frame structure located on the
lot as shown on Figure 1. Ground floors will be structural over crawlspace in the living area and
slab-on-grade in the garcge area. Cut depths are expected to range between about 3 to 5Yz 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 notifîed to re-evaluate the recommendations presented in this report.
Site Conditions: The lot was vacant and the ground surface appeared mostly natural at the time
of our field exploration. The teruain is relatively flat with a strong slope down to the north
towards the Colorado River which borders the north side of the lot. There is a moderately steep
slope down about 6 to 8 feet to the river in the northern part of the lot. The river was a low flow
at this time. Vegetation consists of grass and weeds. The adjacent lots are vacant.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
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 to l% feet of topsoil, consisted of loose, very silty sand
down to depths of from about 2%to 5Yzfeetunderlain by relatively dense, slightly silty sandy
gravel and cobbles (coarse granular soils) down to the pit depths of 6 and 7 feet. Results of
swell-consolidation testing performed on a relatively undisturbed sample of the very silty sand
-2-
soils, presented on Figure 3, indicate moderate to high compressibility under conditions of
Ioading and a wetting with a moderate hydro-compression potential. Results of a gradation
analysis performed on a disturbed bulk sample of underlying coarse granular soils (minus 5-inch
fraction) obtained from site are presented on Figure 4. No groundwater was observed in the pits
at the time of excavation and the subsoils were moist to 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 entirely the undisturbed natural coarse granular soils designed for an allowable bearing
pressure of 2,500 psf for support of the proposed residence. The very silty sand soils are
compressible and should be removed below the footing areas to bear the footings entirely on the
underlying dense coarse granular soils and provide a relatively low risk of settlement. This will
likely require subexcavation below design bearing elevation in areas. It should be feasible to re-
establish design footing bearing elevation with compacted structural fill consisting of imported
single pass "pit-run" sand and gravel or ofaggregate base course'
It is feasible to bear the footings on the upper very silty sand soils with some risk of settlement
and distress. Footings placed on the very silty sand soils should be designed for an allowable
bearing pressure of 1,000 psf. We should further evaluate the feasibility of bearing the footings
on the very silty sand soils at the time of excavation if this is the design approach used'
The footings should be a minimum width of 18 inches for continuous walls and 2 feet for
columns. All topsoil and any 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 and the subgrade compacted. If the footings are designed to bear on the
natural coarse granular soils, all very silty sand soils should also be removed. Structural fill
below footings areas should be compacted to at least 98olo standard Proctor density at a moisture
content near optimum. The structural fill should extend laterally beyond the edges of the
footings a distance equal to at least %the depth of fill below the footings.
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 also 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.
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
Kumar & Assocíates, lnc, @ Project No. 22-7-227
-3-
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 gravel should be placed beneath slabs for support and to facilitate drainage. This
material should consist of minus 2-inch aggregate with less than 50Yo passing the No. 4 sieve and
less than 12% 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 topsoil and oversized (plus 6-inch) rocks, or of suitable imported granular
soils.
Underdrain System: It is our understanding the proposed finished floor elevation at the lowest
level is at or above the surrounding grade. Therefore, a foundation drain system is not required'
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 runoffcan also create a
perched condition. We recommend below-grade construction, such as retaining walls and
basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain and
wall drain system.
If the finished floor elevation of the proposed structure is revised to have a floor level below the
sugounding grade, we should be contacted to provide recommendations for an underdrain
system. All earth retaining structures should be properly drained.
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 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.
3) The ground surface sunounding 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 fîrst l0 feet in pavement and walkway areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation should be located at least
5 feet from the building'
Kumar & Associates, lnc. @ Project No. 22-7-227
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Limitations: This study has been conducted in accordance with generally acce'pted geotechnical
engineering princþles and practices in this area at this time. rtVe make no waranty either
express or implied. The conclusions and recommendations submitted in this report are based
upon the dat¿ obtained from the exploratory pits excavated aI 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 otherbiological 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 evide,lrt 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 implemelrtation of our recommendations, and to veriry 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 sfrata 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 &
David A. Young, P
ts DAY/kac
attachments Figure 1-Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Swell-Çonsolidation Test Results
Figure 4 - Gradation Test Results
Table 1 - Summary of Laboratory Test Results
Kumar & Associates, lnc. o Projec't No. 22-7-227
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LOT 13. THE RAPIDS
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APPROXIMATE SCALE_FEET
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22-7 -227 Kumar & Associates LOCATION OF EXPLORATORY PITS 1Fig.
PIT 1 Ptï 2
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WC= 12.3
DD=85
-200=38 WC=6.5
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LEGEND
TOPSOIL; VERY SILTY SAND, LOOSE, MOIST, DARK BROWN, ROOT ZONE.
SAND (SM); VERY SILTY, LOOSE, MOIST, BROWN
GRAVEL AND COBBLES
BROWN, PRIMARILY ROU
(GM-cP); SANDY, SLIGHTLY SILTY, DENSE, SLIGHTLY MOIST, MIXED
NDED ROCKS.
F
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HAND DRIVE SAMPLE.
DISTURBED BULK SAMPLE
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON MARCH 16,2022
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 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 DEGREE
IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT ÏHE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216):
DD = DRY DENSITY (pcf) (ASTM D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
-200= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1 1 40).
22-7 -227 Kumar & Associates LOGS OF EXPLORATORY PITS li1. 2
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SAMPLE OF: Very Silty Sond
FROM:Pit2E^3'
WC = 6.5 %, DD = 84 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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22-7 -227 Kumar & Associates SWELL_CONSOLIDATION TTST RESULT Fig. 3
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HYOROMETER ANALYSIS SIEVE ANALYSIS
ÎIUE READINGS
2¿ HRS 7 HRS
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U.S. STANDARÐ SERIES OPENINGS
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DIAMETER OF PARTI
CLAY TO SILT COBBLES
GRAVEL A3 % SAND
LIQUID LIMIT
SAMPLE OF: Sondy Grov€l wilh Cobbles
16 %
PLASTICITY INDEX
SILT AND CLAY 1 %
FROM:Pil 1@4'-5'
fheso lorl.6suliË opply only lo lhe
somplos wh¡ch wêre t€slod. Th€
lesllng roport sholl not b€ roproduced,
oxcspt in full, wlthoul lh€ wrlll€n
qpprovol of Kumor & Agggc¡olos. lnc.
Sleve onolysls lesllng ls perlormsd ln
occordoncã wllh ASTM 06913, ASTM 07928,
ASÍM Ct56 ondlor ASTM Dltito.
GRAVELSAND
MEDTUM lcornsE FINE COARSEFINE
Fig. 4GRADATION TEST RTSULTS22-7 -227 Kumar & Associates
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TABLE,I
SUMMARY OF LABORATORY TEST RESULTS
LIMITSGRADATIOI{SAMPLE LOCATION
SOIL TYPÊLIQUID LIMIT
tî/^l IOA\
PLAS'ttC
INDEX
UNCONFINED
COMPRESSIVE
STRENGIH
lôrJl
NATURAL
DRY
DENSTfY
GRAVEL
l%l
SAND
(%l
PERC€NT
PASSING NO.
200 srEvE
Ptf
fft)
DEPTH
NATURÂL
MOISTURE
CONTENT
Very Silty Sand8538I212.3
Sandy Gravel with Cobbles83t64-5
Very Silty Sand6.5 8423
Very Silty Sand3.7 835
No.