HomeMy WebLinkAboutSubsoil Studyl*rtåi'*1fi'å1ifffii5'rnå;å**'
An Employce Owncd Compony
5020 Cournty Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www.kumarusa.com
Office Locations: Dørver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
July 7,2022 RECEIVED
Michael Podmore
P.O. Box 353
New Castle, Colorado 81647
podmoremichael@ gmail. com
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GARFIELD COUNTY
COMMUNITY DEVELOPMËNT
Project No.22-7-376
Subject: Subsoil Study for Foundation Design, Proposed Residence, 3347 County
Road 335, Lot 1, Rapids on the Colorado, Garfield County, Colorado
Dear Mr. Podmore:
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 you dated May 16, 2022. The data obtained and our recommendations
based on the proposed construction and subsurface conditions encountered are presented in this
report.
Proposed Construction: The proposed residence will be one story over a crawlspace with an
attached garage located on the site as shown on Figure 1, The garage floor will be slab-on-grade.
Cut depths are expected to range between about 3 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 signifìcantly different from those described
above, we should be notified to re-evaluate the recommendations presented in this report.
Site Conditions: The site was vacant at the time of our site visit. The previous cabin had been
removed and the crawlspace had been backfilled. The new house will be placed to the north of
the previous cabin. Vegetation at the site consists of cottonwood trees, elm trees and grass. Site
grading appears to be mostly natural. The new house area is on a topographic bench above the
Colorado River to the north. The bench is slightly sloping down to the northwest.
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 1 to IYz feet oftopsoil, consist of
mostly silty sand down to a depth of 6 to 6Yzfeet overlying relatively dense, slightly silty sandy
gravel with cobbles down to the maximum depth explored, 8 feet. About 2 feet of sandy silt and
clay was observed in Pit 2 overlying the sand soils. Results of swell-consolidation testing
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performed on a relatively undisturbed sample of the sandy silt and clay, presented on Figure 3,
indicate low compressibility under existing moisture conditions and light loading and a low to
moderated collapse potential (settlement under constant load) when wetted. No free water was
observed in the pits at the time of excavation and the soils were moist to very moist with depth.
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 sand soil designed for an allowable soil bearing pressure of
1,500 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 and disturbed soils and
existing fill 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 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 backfïll.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly to
moderately 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 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 road base gravel should be placed beneath the garage slab. This
material should consist of minus 1 inch aggregafe with less than 50o/o passing the No. 4 sieve and
less than l2o/o passing the No. 200 sieve.
All fiIl materials for support of floor slabs should be compacted to at least 95Yo af maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
on-site more 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 runoff can create a perched
Kumar & Associates, lnc. o Project No. 22-7-376
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condition. We recommend below-grade construction, such as retaining wa1ls, deep crawlspace
and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain
system. For relatively shallow crawlspaces (less than 4 feet) and garage slab-on-grade, an
underdrain should not be needed.
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 footbelow lowest adjacent fìnish grade and
sloped at a minimum |o/o to a suitable gravity outlet. Free-draining granular material used in the
underdrain system should contain less than 2o/a passing the No. 200 sieve, less than 50% passing
the No. 4 sieve and have a maximum size oî 2 inches. The drain gravel backfill should be at
least 7Yz 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 ofthe foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfìll 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 (if any) 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
backfrll.
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 warranty 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, 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 concerned
about MOBC, then a professional in this special field of practice should be consulted. Our
Kumar & Associates, lnc. o Project No. 22-7-376
-4-
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 pu{poses. lV'e are not
responsible for technical interpretations by others of our infonnation. As the project evolves, we
should provide continued consultation and field sen¡ices during construction to review and
monitor the implementation of our recommendations, and to veriry that the recommendations
have been appropriately interpreted. Significant äesign 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,
Ku¡nar dÈ '{sse¡ci¡¡tes, I
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Daniel E. Hardin, P
DEHlkac
attachments Figure 1-Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Swell-Consolidation Test Results
Table 1 - Summary of Laboratory Test Results
Kumar E Assçciatcs, lnc. 'Projeet No. ?2.?"376
SAMPLE OF: Sondy Sîlt ond Cloy
FROM: Pit 2 @ 1.5'
WC = 9.4 %, DD = 85 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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SWELL_CONSOLIDATION TTST RESULT Fig. 322-7-376 Kumar & Associates
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APPROXIMATE SCALE.FEEÏ
LOCATION OF EXPLORATORY PITS Fig.122-7-376 Kumar & Associates
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WC=9.4
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LEGEND
TOPSOIL; ORGANIC SANDY SILT AND CLAY, WITH SCATTERED GRAVEL AND COBBLES, R00TS,
FIRM, MOIST, BROWN.
SILT AND CLAY (ML-CL); SANDY, MEDIUM STIFF, MOIST, BROWN.
SAND (SV); SILTY, WITH FINE GRAVEL, LOOSE, MOIST, BROWN,
GRAVEL (CV); SIIIOY, SLIGHTLY SILTY WITH COBBLES, DENSE, MOIST, BROWN.
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HAND DRIVE SAMPLE.
DISTURBED BULK SAMPLE
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON MAY lE, 2422.
2. THE LOCATIONS OF TIIE 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. PIT 2 WAS ABOUT 1 FOOT HIGHER THAN PIT 1.
4. THE EXPLORATORY PIT LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO ÏHE DEGREE
IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETì,VEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AÏ THE TIME OF EXCAVATION.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pct) (lsrv ù 2216);
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D I14O).
Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 222-7 -376