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An Employe Orncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
October 12,2023
Crawford Design Build
Attn: Don Glenn
P.O. Box 1236
Carbondale, Colorado 81623
crawforddesi gnbuild@comcast.net
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JAN 2 4 2025
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Subject:
Project No.23-7-590
Subsoil Study for Foundation Design, Proposed Residence, Lot 8, Wooden Deer,
Wooden Deer Road, Garfield County, Colorado
Dear Don:
As requested, Kumar & Associates, Inc. observed two backhoe pits for design of foundations at
the subject site. The study was conducted in accordance with oru agreement for geotechnical
engineering services to Crawford Design Build dated October 6,2023. The data obtained and
our recommendations based on the proposed construction and subsurface conditions encountered
are presented in this report.
Proposed Construction: We assume the proposed residence will be a fwo-story wood frame
structure located in the area of the pits on the site. Ground floor will be with slab-on-grade or
structural crawlspace. Cut depths are expected to range between about 5 to 12 feet. Foundation
loadings for this type of consffuction 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 is undeveloped and slopes moderately steeply down to the east-
southeast. There is a steep road cut down to Wooden Deer Road to the east. Two pits had been
excavated with a mini-excavator in the lower part of the building area. The site is vegetated with
pinon and cedar trees with an understory of grass and weeds.
Subsurface Conditions: The subsurface conditions at the site were evaluated by observing two
backhoe pits previously excavated in the lower portion of the proposed building area. The
subsoils encountered, below about 1 foot of topsoil, consist of 9 feet of silty sand with scattered
gravel and cobble to small boulder size basalt rocks. Results of consolidation testing performed
on a relatively undisturbed sample of the silty sand matrix soils, presented on Figure 1, indicate
low compressibility under existing moisture conditions and light loading and a low settlement
potential when wetted. The soils were moderately compressible under increased loading after
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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 thc naturc of the proposed construction, we recommend spread footings
placed on the undisturbcd natural 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 and 2 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 lengh of at least 12 feet. Foundation walls acting as retaining
structures should be designed to resist a lateral earfh pressrrre hased 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 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 free-draining gravel should be placed beneath basement level
slabs to facilitate drainage. This material should consist of minus 2-inch aggregate with less
than50%o passing the No. 4 sieve and less than2Vo 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 runoffcan create a perched
condition. We recommend below-grade construction, such as retaining walls, crawlspace and
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 surroundcd abovc
the invert level with free-draining granular material. The drain should be placed at each level of
Kumar & Associatel, lnc. o Project No. 23-7-590
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excavation and at least I foot below lowest adjacent finish grade and sloped at a minimum lVo to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2Yo 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 l7zfeet 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 90Yo 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 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 areas. A swale may be
needed uphill to direct surface runoffaround the residence.
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. Consideration should be given to the use of xeriscape to
limit potential wetting of soils below the foundation caused by irrigation.
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 site, 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 findings include interpolation and extrapolation of the
subsurface conditions identified atthe exploratory pits and variations in the subsurface
conditions may not become evident until excavation is performed. If conditions encountered
during constrrction appear different from those described in this report, we should be notified at
once so re-evaluation of the rscommendations 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
Kumar & Associates, lnc. o Project No. 23-7-590
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should provide continued consultation and field services during construction to review and
monitor the implanentation of our recommendations, and to verifu 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 strata and testing of structural fill by a representative of
the geoteclurical engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
Kumar & Associates,
Daniel E. Hardin, P
DEH/kac
ottachment Figure I Test Results
Kumar & Associates, lnc, o Project No. 23-7-590
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