HomeMy WebLinkAboutFile Documents.134 E Bleeker St.0102-2020-BRES (40) Ic+A &Kumar Associates,
Geotechnical Aland Materialss Engineers 5020 County Road 154
and Environmental Scientists Glenwood Springs,CO 81601
phone:(970)945-7988
fax: (970)945-8454
email:kaglenwood@kumarusa.com
An Employee Owned Company www.kumarusa.com
Office Locations: Denver(HQ),Parker,Colorado Springs,Fort Collins,Glenwood Springs,and Summit County,Colorado
July 2, 2020
Eigelberger Architecture+Design
Attn: Nick Chan
350 Market Street, Suite 309
Basalt, Colorado 81621
(nchan@eigelberger.com)
Project No. 20-7-375
Subject: Summary Soils Report, Proposed Full Basement and Crawlspace Under Existing
House, 134 East Bleeker Street, Aspen, Colorado
Dear Nick:
As requested, Kumar&Associates, Inc. is providing this summary soils report for preliminary
design of foundations at the subject site. Access into the site with a drill rig is not practical at
this time. Our recommendations are based on previous subsoil studies performed in the area as
verbally requested via email on May 13, 2020 and amended to our agreement for geotechnical
engineering services to you dated May 15, 2020. We have previously performed at least half a
dozen subsoil studies within a block of the subject site. Our recommendations are based on the
proposed construction and subsurface conditions previously encountered in the area.
Proposed Construction: The proposed full basement over crawlspace will be placed below the
existing residence. Cut depths are expected to range up to about 22 feet. Foundation loadings
for this type of construction are assumed to be relatively light and typical of the proposed type of
construction. Excavation shoring will be provided as needed to maintain cut slope stability.
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 relatively flat and occupied by an existing one and two story
residence with mature landscaping.
RECEIVED
09/03/2020
ASPEN
BUILDING DEPARTMENT
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Subsurface Conditions: The subsurface conditions encountered in this area typically consist of
about 5 feet of gravel fill overlying relatively dense gravel alluvium. There can be layers of
alluvial sand within the gravel. The gravel alluvium is expected to extend down at least 50 feet
and groundwater is expected to be at least 50 feet below the site. The bearing soils at proposed
cut depth are expected to be relatively dense, slightly silty, sandy gravel with cobbles and small
boulders.
Foundation Recommendations: Considering the subsoil conditions encountered in the area
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 3,000 psf for support
of the proposed new foundation. Footings should be a minimum width of 16 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 gravel soils. Exterior footings should be
provided with adequate cover above their bearing elevations for frost protection. Placement of
footings at least 42 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
structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit
weight of at least 45 pcf for the on-site soil as backfill. The coefficient of friction of 0.50 can be
used to resist sliding on the bottom of footings. An equivalent fluid unit weight of 425 pcf can
be used to resist lateral loads on the sides of footings.
Floor Slabs: The natural on-site soils, exclusive of fill and 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
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 than 50%passing the No. 4
sieve and less than 2%passing the No. 200 sieve. RECEIVED
09/03/2020
Kumar&Associates,Inc.® Project No. 20-7-375
i\SPEN
BUILDING DEPARTMENT
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All fill materials for support of floor slabs should be compacted to at least 95% 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 is not expected to be encountered in the excavation, 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 also 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 perforated rigid 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 1 foot below lowest adjacent finish grade and
sloped at a minimum 1/2%to a suitable outlet such as a drywell or sump and pump. Free-draining
granular material used in the underdrain system should contain less than 2%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 11/2 feet deep. Percolation tests performed in this area indicate
the natural gravel soils are relatively free draining.
Surface Drainage: The NRCS mapping shows Type B soil for this area of Aspen. The
following drainage precautions should be observed during construction and maintained at all
times after the project 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 98% 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 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 mininTE 1 E IVE D
09/03/2020
Kumar&Associates,Inc.® Project No. 20-7-375
i\SPEN
BUILDING DEPARTMENT
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slope of 16 inches in the first 10 feet in unpaved areas and a minimum slope of
21/2 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 report is based on subsoil conditions previously encountered for nearby
projects. We make no warranty either express or implied. The conclusions and
recommendations submitted in this report are based upon 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. Variations in the
subsurface conditions may not become evident until excavation is performed.
This report has been prepared for the exclusive use by our client for preliminary design purposes.
We are not responsible for technical interpretations by others of our information. As the project
evolves, we should perform subsurface exploration for foundation design, provide continued
consultation and monitor the implementation of our recommendations to verify that the
recommendations have been appropriately interpreted. Significant design changes may require
additional analysis or modifications to the recommendations presented herein.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
Kumar& Associates, Inc.
,(/ ( ' .. •�Y •'11,
Daniel E. Hardin,P.E.
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cc: Eigelberger Architecture—Hannah Hunt Moeller(hannahhunt(a,eigelberger.com)
KL&A—Brett McElvain (bmcelvain@klaa.com) RECEIVED
0-910 31 L02 0
Kumar&Associates,Inc.® Project No. 20-7-375
ASPEN
BUILDING DEPARTMENT