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July 1,2013
Michael Lauterbach
P. O. Box 5026
Edwards, Colorado 81632
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Job No. ll3 2421'
Subject:observation of site conditions and Presumptive soil Bearing pressure,
Proposed Residence, Lot SDl7 (formerly Lot L3), Aspen Glen,
Sundance Trail, Garfield Count¡ Colorado
Dear Mr. Lauterbach:
As requested, Hepworth-Pawlak Geotechnical has reviewed the subject site conditions
with respect to providing a presumptive soil bearing capacity for a spread footing
foundation to support the proposed residence, The findings of ow site observations and
preliminary recoilmendations for the foundation design are presented in this report. The
services were performed in accordance with our agreement for professional engineering
services to you, datecl July l, 2û13.
Proposed Construction: The residence will be about 2,500 square fect, one story, wood
frame structure over a crawlspace. The attached 650 square foot garage will have a slab-
on-grade floor. Foundation loadings arc assumed to be relatively light and typical of the
proposed construction.
Site Conditions: We observed the site conditions on July 1 ,2013. The lot is vacant and
the ground surface appears to have been graded during original subdivision development.
The terrain is relatively flat rvith a slight slope down to the south. Elevation difference
across the proposed building is about I foot. There is an irrigatjon ditch along the east
side of the lot that was running at the time of our site visit. The lot is bordered on the
north side by Sundance Trail and to the south by a pond. The lots to the east and west are
also vacant. The subsoils in this area typically consist of up to 5 feet of sandy silty clay
overlying relatively dense gravel soils.
Subsidence Potential: Aspen Glen Subdivision is underlain by Pennsylvania Age Eagle
Valley Evaporite bedrock. The evaporite contains gypsum deposits. Dissolution of the
gypsum under certain conditions can cause sinkholes to develop and can produce areas of
localized subsidence. During previous work in the area, sinkholes were observed
scattered in the Aspen glen development. The nearest mapped sinkhole is about 200 feet
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Michaei Lauterbach
July l, 2013
Page2
to the northwest ofthis site. Sinkholes were not observed in the immediate area ofthe
subject 1ot. Based on our present knowledge ofthe site, it cannot be said for certain that
sinkholes will not develop. In our opinion, the risk of ground subsidence at Lot SD17 is
iow and similar to other lots in the area but the owner should be aware of the potential for
sinkhole development.
Preliminary RecommendatÍons: Based on the site conditions and our experience in the
area, it should be feasible to support the building on lightly loaded spreád foctings with
some risk of settlement. The risk of settlement is primarily if the bearing soils become
wetted and precautions, such as positive surface drainage away from foundation walis and
adequate compaction of foundation backfill, should be taken to prevent wetting.
Differential settlement risk may also be from variable soil bearing areas. For preliminary
design of the footings, an allowable soil bearing pressure of 1,5û0 psf can be assumed.'We should observe the foundation excavation at the time of construction to evaluate the
soil bearing conditions exposed. If the soil bearing conditions are different than assumed,
the foundation may need to be re-designed.
The spread footings should be a minimum width of 18 inches for continuous walls and Z
feet for columns. All topsoil and loose disturbed soils in footing areas should be removed
and the bearing level extended down to the undisturbed natural soils. The footing
subgrade should then be moistened and compacted. Exterior footings should be provided
with adequate soil cover above their bearing elevations for frost protection. 'We
recomrnend 36 inches of frost cover be used. 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 on-site soil, excluding topsoil and oversized rocks, as backfill. Any
foundation walls acting as retaining structures should be provided with an underdrain
system to prevent temporarybuildup of hydrostatic pressure. Structural fill placed within
floor slab areas can consist ofthe on-site soils compacted to at least 95% of standard
Proctor density (SPD) at a moisture content near optimurn Backfill placed around the
structure should be compacted to at least 90% SPD and the surface graded to prevent
ponding within at least 10 feet of the building. Landscape that requires regular heavy
irrigation, such as sod, and sprinkler heads should not be located within 5 feet ofthe
foundation.
Limitations: The recommendations submitted in this letter are based on our observation
of the site conditions and our experience in the area, and did not include subsurface
exploration to evaluate the subsurface conditions within the loaded depth of foundation
influence. The risk of foundation movement may be greater than indicated in this report
Job No. 113 242A
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Michael Lauterbach
July 1, 2013
Page 3
because ofpossible variations in the subsurface conditions. It is possible the data
obtained by subsurface exploration could change the recommendations contained in this
letter. We should observe the foundation excavation at the time of construction to
evaluate the soil bearing conditions.
Our services do not include determining the presence, prevention or possibility ofmold or
other biological contaminants (MOBC) developing in the future. If the client is
concemed about MOBC, then a professional in this special field of practice should be
consulted. We
Ifyou have any questions or need firther assistance, please call our ofñce.
Sincerel¡
HEPV/ORTH * PAWLAK GEOTECHNICAL, INC
Daniel E. Hardin, P.E.
DEHiljg
Job No. 713 242A
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