HomeMy WebLinkAboutObservation of Excavation 10.20.11HEPWORTH-PAWLAK GEOTECHNICAL
October 20, 2011
Aspen Custom Builders
Attn: John Davis
P. O. Box 966
Basalt, Colorado 81623
john@aspencustombuilder. com
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Job No. 111 078A
Subject: Observation of Excavation, Proposed Residence, 7330 County Road 100,
North of Fire Station, Missouri Heights, Garfield County, Colorado
Dear Mr. Davis:
As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the
excavation at the subject site on October 18, 2011 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 performed as additional
services in accordance with our agreement for professional engineering services to Aspen
Custom Builders, dated April 20, 2011. We previously provided a subsoil study for this
project dated May 24, 2011, Job No. 111 078A.
At the time of our visit to the site, the foundation excavation had been cut in four levels
from 3 to 18 feet below the adjacent ground surface. The soils exposed in the bottom of
the excavation consisted of basalt gravel, cobbles and boulders in a highly calcareous
sandy silt and clay matrix. No free water was encountered in the excavation and the soils
were slightly moist.
Considering the conditions exposed in the excavation and the nature of the proposed
construction, spread footings placed on the undisturbed natural soil designed for an
allowable soil bearing pressure of 2,500 psf should be adequate for support of the
proposed residence. The matrix portion of the exposed soils tends to compress when
wetted and there could be some post -construction settlement of the foundation if the
bearing soils become wet. The subgrade soils should be moistened and compacted prior
to placement of concrete. Other recommendations contained in our previous report
should also be followed.
We understand that it is desired to use a thickened slab section for interior bearing walls
rather than spread footings separate from the slab -on -grade as recommended in our
previous report. There is a risk of cracking of the slab at the edge of the thickened
portion and we recommend that additional reinforcement be placed across this transition
area to reduce the risk of differential movement of the slab. The thickened slab approach
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Aspen Custom Builders
October 20, 2011
Page 2
can be used provided the owner is aware of the potential for cracking and possible
movement due to the differential loading on the thickened parts of the slab.
The recommendations submitted in this letter are based on our observation of the soils
exposed within the foundation excavation 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. 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 GEOTCHMCAL, INC.
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cc: Kurtz & Associates — Attn: Brian Kurtz
Job No, 111 078A
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