HomeMy WebLinkAboutObservation of Excavation 11.17.2007Fell
HEPWORTH - PAWLAK GEOTECHNICAL
November 17, 2011
Tim Boyle
8877 County Road 115
Glenwood Springs, Colorado 81601
f3iatiru44{a)hotmuail.co m
Job No. 109 173A
Subject: Observation of Excavation, Proposed Barn, 8877 County Road 115,
Garfield County, Colorado
Dear Tim:
As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the
building excavation at the subject site on November 11, 2011 to evaluate the materials
exposed for foundation support. The findings of our observations and recorrunendations
for the foundation design are presented in this report. We previously observed the
excavation for your residence at the subject site and presented foundation design
recommendations in a report dated June 3, 2009, Job No. l09 173A. The current services
are in addition to our previous agreement for professional services with you dated May
28, 2009.
The proposed barn site has been developed by cutting up to about 12 feet deep at the
north side and filling up to about 8 feet deep at the south side. The building will be a pre-
engineered steel structure supported by 10 isolated pad footings imposing an allowable
bearing pressure up to 2,500 psf. We understand that a floor slab is not proposed at this
time but could be constructed some time in the fixture.
At the time of our visit to the site, the footing pad excavations had each been cut to a
depth of about 4 feet below the adjacent ground surface. The southern 5 pad excavations
were typically based in very firm, natural silty sandy gravel. An organic soil layer about
one foot thick was exposed immediately above the cut depth. Above that was recently
placed fill from the building site grading. There was some organic material remaining in
the bottom of the southern pad excavation which we recornmended be removed. The
northern 5 pad excavations were based in hard sandstone bedrock. The results of a
gradation analysis performed on a sample of the silty sandy gravel (minus 3 inch fraction)
obtained from the 2" excavation from the southwest corner are presented on Figure 1.
No free water was encountered in the pad excavations and the soils and rock were slightly
moist.
The soil and rock conditions exposed in the excavations are similar to those previously
encountered on the site and suitable for support of spread footings designed for an
Tim Boyle
November 17, 2011
Page 2
allowable bearing pressure of 2,500 psf. Some differential settlement should be expected
if the silty bearing soils of the south building line are wetted. Loose disturbed soils, rock
and any remaining organic soils should be removed in the footing areas to expose the
undisturbed natural gravel soils or rock. The bearing soils should be protected from frost
and concrete should not be placed on frozen soils. The compaction of the existing fill has
not been documented. Due to the variable slab bearing conditions between the sandstone
northern part and the fill southern part, there is a potential for some differential fill
settlement and slab cracking. Tim Boyle stated that the fill will be removed and replaced
with compacted structural granular fill prior to placement of the slab -on -grade. Other
recommendations presented in our previous report that are applicable should also be
observed.
The recommendations submitted in this letter are based on our observation of the
materials exposed within the foundation excavations at the site. Variations in the
subsurface conditions below the excavations 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.
Rev. by: DEH
SLPrksw
Attachment: Figure I Gradation Test Results
cc: Albright & Associates Jack Albright (iackfti-albri:dit-also 47te
Job No W9 17 A
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