HomeMy WebLinkAboutSubsoil Study for Foundation Design 09.17.2024lGrf $ffiffiffi;!i8'**
An Employcr onrnod Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone; (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumanrsa.com
www.kumarusa.com
Office locations: Denvo (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
September 17,2024
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Annie Perry 6lif ,,.,,.,,, ' # r, .
88 Cedar Street """'.,rrril,,',!-t,
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Carbondale, Colorado 81623 '".'i',.;1 ,
batadogo@gmail.com
Project No.24.7-459
Subject: Subsoil Study for Foundation Design, Proposed Residence, 55 S. Cedar Street,
Carbondale, Colorado
DearMs. Perry:
As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations at
the zubject site. The study was conducted in accordance with our agreement for geotechnical
engineering services to you dated August 6,2024. The data obtained and ourrecommendations
based on the proposed construction and subsurface conditions encountered are presented in this
report.
Proposed Construction: The proposed residence will be a one to two story wood frame
structure, tentatively located on the north side of the site in the area of Pits 2 and 3 with *re
sepfic field in the area of Pit I as shown on Figure l. Ground floor will be structural over
crawlspace or slab-on-grade. Cut depths are expected to range between about 3 to 5 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 site was occupied by several older, wood frame structures, all of which
will be removed prior to new construction. Vegetation consists of several large deciduous and
fir trees with a mostly grass understory. The site is relatively flat with a gentle slope down to
the east. A small dry pond excavation is located in the southeast comer of the property. The
site is bordered to the west by Cedar Streeq to the east by a parking area and to the north and
south by other residential properly. There is an active irrigation ditch along the southwest side
of the property and then turning east through the northern part of the properly.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
four exploratory pits at the approximate locations shown on Figure l. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about up to one foot of topsoil, consist
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of I to 4 feet of clayey silty sand overlying relatively dense, slightly silty, sandy gravel with
cobbles and scattered small boulders. Results of swell-consolidation testing performed on a
relatively undisturbed sample of the clayey silty sand, presented on Figwe 3, indicate low
compressibility under light to moderate loading and a minor settlement potential when wetted.
No free water was observed in the pits at the time of excavation and the soils were moist to
slightly 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 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 16 inches for continuous walls and2 feet for columns. I-oose 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 10 feet. Foundation walls acting as retaining
stnrctures 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.
f,'loor 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 unresfiained vertical movement. Floor slab control joints should be used
to reduce damage due to shrinkage cracking. The requirements forjoint spacing and slab
reinforcement should be established by the designer based 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 50o/o passing the No. 4 sieve and less than2Yo 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, crawlspace and
Kumar & Agsociates, lnc. o PrcJect No. 2&7459
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basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain
system.
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 of
excavation and at least I foot below lowest adjacent finish grade and sloped at a minimum lYoto
a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain
system should contain less than 2Yopassrngthe No. 200 sieve, less than 50% passing the No. 4
sieve and have a manimum size of 2 inches. The drain gravel backfill should be at least lYz 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 95% 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 capped with about 2 feet of the on-site, finer
graded soils to reduce surface water infiltation.
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 inunpaved 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 arezat this time. We make no warranty either
express or implied. The conclusions and recommendations submitted in this report me 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,theproposed type of construction, and our experience in
the area. Our services do not include determining the presence, prevention or possibility of nrold
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. Ow
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.
Kumar &Asgociates, lnc. o Project No. 24.7459
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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 wolves,
we should provide continued consultation and field senrices during constnrction to review and
monitor the implementation of our recommendations, and to vgrtfy that the recommendations
have been appropriately interpreted. $ignificant design changes may require additional analysis
or modifications to the recommendations presented hercin. We recommend on-site obseryation
of excavations and foundation bearing sfiata and testing of shrctrnal fill by a representative of
the geotechnical engineer.
If you have any questions or if we may be of firrther assistance, please let us know.
Respectfully Submitted,
Kumar & Assochtes, lnc.
Daniel E. Hardin, P.E.
Reviewed by:
,l
Robert L. Duran, P.E.
DEHftac
attachments Figure I - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Swell-Consolidation Test Results
cc:Sopris Engineering - Paul Rutledge (prutledse@sopris€ng.com)
Terralink Shrctures - Keith Brand (teith@tegatrnkqtguctures.com)
Kumar &Associates, lnc. o Project No. 24-7459
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24-7-459 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
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PIT 1 PIT 2 PIT 5 PIT /+
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WC=14.9
DD=99
-200=58
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LEGEND
TOPSOIL; oRGANlc SILTY SAND TO SANDY SILT.
POND EXCAVATION.
SAND (SC); CLAYEY, SILTY MEDIUM STIFF, MOIST, BROWN
cRAvEL (CU-Cp);
BOULDERS, DENSE,
SANDY, SLIGHTLY SILTY, WITH COBBLES AND SCATTERED SMALL
MOIST, BROWN.
F
HAND DRIVE SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON AUGUST 21, 2021.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPTH.
1. THE EXPLORATORY PIT LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE
IMPL]ED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL WPES 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 CONTENT (U) (ASTM D 2216);
DD = DRY DENSIil (pcf) (ASTM D 2216);
-2Oo= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140)
24-7-459 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
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SAMPLE OF: Cloycy Siliy Sond
FROM:PlltO5.5'
WC = 11.9 %, DD = 99 pcf
-2OO = 1O %
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ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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24-7-459 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3