HomeMy WebLinkAboutObservation of Excavation 10.29.2014: _,--i=WOR T F HR4WL K -_ EO- [C - N!CAL
October 29, 2014
D.M. Neuman Construction
Attn: Jason Neuman
P.O. Box 2317
Glenwood Springs, Colorado 81602
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Subject:
Dear Jason:
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Job No. 114 393A
Observation of Excavation, Proposed Shop Building, 8984 County Road
117, South of Glenwood Springs, Garfield County, Colorado
As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the
excavation at the subject site on October 28 and 29, 2014 to evaluate the soils exposed for
foundation support. The findings of our observations and recommendations for the
foundation design are presented in this report. We previously conducted a subsoil study
for design of foundations at the site and presented our findings in a report dated
September 30, 2014, Job No. 114 393A.
The proposed construction includes a single level shop building with access drive and
septic disposal field. The building will be wood frame construction with a slab -on -grade
floor. Spread footings bearing on the natural granular soil with an allowable bearing
pressure of 2,500 psf were recommended in the referenced subsoil study for the project.
At the time of our initial visit to the site, the perimeter foundation excavation had been
cut in one level from 1'A to 4 feet below the adjacent ground surface. The soils exposed
in the bottom of the excavation consist primarily of clayey sand with gravel. The north
side foundation excavation reportedly had approximately 2 feet of unsuitable soil below
foundation grade that was removed prior to our site visit. The over -excavated soils had
been replaced with compacted 3/" aggregate base course that was reportedly compacted
with a walk behind double drum compactor. Soils exposed in the bottom of the south
footing excavation consisted of sandy clay. The clay soils were estimated to be about 1
foot thick and were recommended to be removed from the foundation areas in a phone
conversation with Jarrid Hadland with D.M. Neuman. When observed on October 29, the
fine-grained soils had been removed and the south foundation area was stepped down
about 10 inches to expose the natural granular soils. During our site visit on October 29,
it was observed that the granular soils contained a wet clay matrix that appeared unstable
under foot traffic but contained gravel and cobbles throughout. It was recommended to
Jeff Peterson that a lightly loaded footing may be used to span the wet clay matrix soils
on the south end. No free water was encountered in the excavation and the soils were
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D.M. Neuman
October 29, 2014
Page 2
generally moist and wet on the south end. We understand that the trench drain installed
just outboard of the south footing line is flowing water at a depth of about 14 inches
below footing excavation depth.
The natural firm soils exposed in the east and west wall line excavations and compacted
structural fill on the north end are suitable for support of spread footings designed for the
recommended allowable bearing pressure of 2,500 psf. The footing on the south wall line
can be designed for an allowable bearing pressure of 1,500. We understand that the
design bearing pressure is less than 1,500 psf and the contractor also elected to use a
wider footing of 24 inches, further reducing the bearing pressure. Loose disturbed soils
should be removed as needed to expose the undisturbed natural granular soils. Structural
fill used in foundation areas should consist of imported granular material, such as CDOT
Class 6 aggregate base course, placed in 8 inch maximum loose lifts and compacted to a
minimum of 98 percent of the standard Proctor value for the material near optimum
moisture content. Any water seepage into the excavation should be collected and diverted
away from the footing areas and any softened soils and mud removed before concrete
placement. The bearing soils should be protected from frost and concrete should not be
placed on frozen soils. Other recommendations presented in our previous report which
are applicable should also be observed.
The recommendations submitted in this letter are based on our observation of the soils
exposed within the foundation excavation and the previous limited subsurface exploration
at the site. Variations in the subsurface conditions below the excavation could increase
the risk of foundation movement. We should be advised of any variations encountered in
the excavation conditions for possible changes to 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
concerned about MOBC, then a professional in this special field of practice should be
consulted.
If you have any questions or need further assistance, please call our office.
Sincerely,
HEPWORTH — PAWLAK GEOTECHNICAL, INC.
Steven L. Pawlak P.E.
Rev. by: JAP
SLP/ksw
cc: D.M. Neuman — Jan -id (j ii(«.clrntteuu1an.eom)
Job No. 114 393A
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