HomeMy WebLinkAboutObservation of Excavation 08.06.2021lftrf mm,m:if"'-" a- 7' //
An Employee Ou¡ned Compcny
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
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Ofice Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
August 6,2421
DenverHayes
P. O. Box 471
Meeker, Colorado 81641
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hoject No.2l-7-642
Subject Obsenration of Exc¿vation, Proposed Buokhouse,1952 County Road 132
(Mitchel Creek RoaQ, Garfield County, Colorado
Dear Denver:
As requeskd, a representative of Kumar & Associates oblerved the excavation at the subject site
on August 3,2021to ev¿lu¿te tlre soils exposed for foundation support. The findings of our
observations and recommend¿tions are presented in this report- The service$ $¿ere perfiormed in
accordance with our agreement for professional engineering services to you dated August 2,
2021.
The building will be a single-story log stnrcture over a basement level. The ground floor will be
slab-on-grade. The building has been designed to be zupported on spread footings assuming an
allowable soil bearing pressure of 2,00Ûpsf by the sbn¡ctural engineer.
At the time of our sile visit, the foundation excavation had been cut in three levels from about
I to 6 feet below the adjacent ground surface. The soils exposed in the bottom of the excavation
consistd of medium dense, silty sandy gravel with cobbles. The excavation subgrade had not
been compacted. The results of a gradation analysis performed on a sample of the soils (minus
3-inch fraction) obt¿ined from the siæ are presented on Figure l. No free water was elrcountered
in the excavation and the soils were slightly moist.
Considering the conditions exposed in the excavåtion and the nature ofthe proposed
construction, spread footings placed on the undisturbed natural granular soils designed for an
allowable bearing pressure of 2,ffi0 psf can be used for support of the proposed building. The
exposed soils may tend to compress some when wetted and there could be some post-
construction settlement of the foundation if the bearing soils become wet, and precautions should
be taken to prevent wetting. Footings should be a minimum width of l8 inchos for continuous
walls and 2 feet for columns. Loose and distr¡rbed soils in footing areas should be removed and
the bearing level extended down to the undisturbednatural soils, and the subgrade moistened and
compected. Exterior footings should be provided with adequaæ soil cover above their bearing
elevations for frost protection. 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 stn¡ctures should also be desigued to resist a lateral earth
pressure b¿sed on an equivalent ftuid unit weight of at least 50 pcf for on-site soil as backfill. A
Denver Hayes
August 6,2021
Page2
perimeter foundation drain should be provided to prevent te,rnporary buildup of hydrostatic
pressure behind the basement walls and prevent wetting ofthe lower level. Structural fill placed
within floor slab areas can consist of the on-site soils compacted to at least 95% of standard
Proctor density (SPD) at a moisture content near optimum. Backfill placed around the structure
should be compacted to at least 90% SPD and the surface graded to prevent ponding within at
least l0 feet of the building. Landscape that requires regular heavy irrigation, such as sod, and
sprinkler heads should not be located within l0 feet of the foundation.
The recommendations submitted in this letter are based on our observation of the soils exposed
within the foundation exþavation and do not include subsurface exploration to evaluate the
subsurface conditions within the loaded depth of foundation influence. This study is based on
the assumption that soils beneath the footings have equal or better support than those exposed.
The risk of foundation movement may be greater than indicated in this report because of possible
variations in the subsurface conditions. In order to reveal the nature and extent of variations in
the subsurface conditions below the excavation, drilling would be required. It is possible the
data obtained by subsurface exploration could change the recommendations contained in this
letter. 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 concemed about
MOBC, then a professional in this special field ofpractice should be consulted.
If you have any questions or need further assistance, please call our office.
Sincerely,
David A. Young P
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21-7-642 Kumar & Associates GRADATION TEST RESULTS Fig. 1