HomeMy WebLinkAboutObservation of Excavation 05.20.2019t(+rtåffiåffiffir#ü*""
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An Emdoyee Otflnsd Gompony
5020 Cirunty Road 154
Glenwood Springs, C() 8ll¡01
phone; (970) 945-79¡t8
lâx: (970) 945-84.54
eurai l: kaglenwood(a)kumarusa.com
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Oflìce Lrrcaticns; llelver (llQ), i'arkcr, {lolo¡arlo Sprilgs, Fort Collins, Clenwood Springs, aml Summit County, Colorarlo
May 20,2019
Anclrew Reeves
P.O. Box 824
Silt, Colorado 81652
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Subject
Project No. 19-7-133
Observation of Excavation, Proposed Attached Garage, 5323 County Road 309,
Rulison, Garfielcl County, Colorado
Dear Andrew
As requested, a representative of Kumar & Associates observed the excavation at the subject site
on May 16,2019 to evaluate the soils exposed for foundation support. The findings of our
observations and recommendations for the foundation design are presented in this report. The
services were perfonned in accordance with our agreement for professional engineering services
to you, dated February 7 ,2019.
The proposed garage will be attached to the existing house. It will be a 1 story structure with
plans to build an ADU above the garage. Ground floor will be slab-on-grade. The foundation is
planned to be supported by spread footings designed assuming an allowable bearing pressure of
1,500 psf.
At the time of our visit to the site, the foundation excavation had been cut in 3 levels from 3 to
3Yz feet below the adjacent ground surface. The soils exposed in the bottom ofthe excavation
consisted of interlayered sandy silt and clay and silty gravel and sand. Results of swell-
consolidation testing performed on the finer-grained samples taken from the site, shown on
Figures I and2, indicate the soils are compressible under conditions of loading and wetting and
have a low to moderate collapse potential (settlement urder constant load) when wetted. No free
water was encountered in the excavation and the soils were slightly moist to moist.
Considering the conditions exposed in the excavation and the nature of the proposed
construction, sprcad footings placed on the undisturbed natural soil designed for an allowable
soil bearing pressure of 1,500 psf can be used for support of the proposed garage with a
settlement and distress risk. The exposed soils tend to compress when wetted and there could be
post-construction settlement of the foundation depending on the depth and extent of the bearing
soil wetting. Footings should be a minimurn width of 18 inches for continuous walls and 2 feet
for columns. Loose disturbed soils in footing areas should be removed and the exposed bearing
soils moistened and cornpacted. Extedor footings should be provided with adequate soil cover
above their bearing elevations for frost protection. Continuous foundation walls should be
Andrew Reeves
N4ay 20,2019
Page2
reinforced top and bottom to span local anomalies such as by assuming an unsupported lenglh of
at least 12 feet. Foundation walls acting as retaining structures (if any) 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 as backfill. A perirneter foundation drain should not be providetl for the proposed slab-
at-grade construction. Structural fill placed within floor slab areas oan consist of the on-site soils
compacted to at least 95% of standard Proctor density at a moisture content near optimum.
Backfill placed around the structure should be compacted and the surface graded to prevent
pondipg 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 l0 feet of the foundation.
The recommendations submitted in this letter are based on our observation of the soils exposed
within the foundation excavation ancl 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 fbotings 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 subsurfhce 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 of practice should be consulted.
lf you have any questions or need fu*her assistance, please call our offtce.
Sincerely,
Kumar & Associates, fnc.
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Yzt '+fuÍames H. Parsons, E.L
Reviewed by:
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Steven L. Pawlak,
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Attachment:
Kumar & Associates, lnc. È
ra'cll Consolidation Test Results
Project No. 19"7-133