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December 19, 2014
Desmond Home Builders
Attn: Bryan Desmond
P.O. Box 3518
Eagle, Colorado 81631
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Job No. 114 189A
Subject: Observation of Excavation, Northern Portion of Proposed Duplex, Lot 2,
Bighorn Estates, 4288 Nugget Lane, Vail, Colorado
Dear Bryan:
As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the
excavation at the subject site on December 18, 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. The services were supplemental to our
proposal for professional engineering services to Desmond Home Builders, dated May
14, 2014. We previously observed the southern portion of the excavation and presented
our findings in a report dated October 14, 2014, Job No. 114 189A.
The duplex will be a multilevel structure cut into and retaining the hillside slope. Ground
floors will be slab-on-grade. The foundation design for the building was based on a
previous soil and foundation investigation at the site by LKP Engineering dated October
1, 2003, Project No. 03148. The report recommended spread footings designed using an
allowable soil bearing pressure of 1,500 psf for foundation support. We have been
provided a copy of that report. The foundation excavation for the building was done in
two phases with the southern portion done previously and the northern portion completed
currently.
At the time of our site visit, the foundation excavation for the northern portion of the
building had been cut in three levels from about 5 to 15 feet below the adjacent ground
surface. The soils exposed in the bottom of the excavation consisted of medium dense,
silty sand with gravel and scattered cobbles and boulders. Completed footing excavation
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Desmond Home Builders
December 19,2014
Page 2
areas had been compacted using a remote controlled vibratory double drum roller.
Results of swell-consolidation testing performed on a sample taken from the site, shown
on Figure 1, indicate the soils are slightly to moderately compressible under conditions of
loading and wetting. No free water was encountered in the excavation and the soils were
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 bearing pressure of 1,500 psf can be used for support of the proposed building.
The exposed soils tend to compress especially when wetted under loading 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 16 inches for continuous walls and 2 feet for columns. Any loose or disturbed soils in
footing areas should be removed or re-compacted. The bearing soils should be protected
against frost and concrete should not be placed on frozen soils. Exterior footings should
be provided with adequate 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 structures should also be designed to resist a lateral earth
pressure based on an equivalent fluid unit weight of at least 55 pcf for on-site soil as
backfill. A perimeter foundation drain should be provided to prevent temporary buildup
of hydrostatic pressure behind the basement walls and prevent wetting of the 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 near optimum moisture content.
Backfill placed around the structure should be compacted to at least 90% SPD and the
surface graded to prevent ponding within at least 10 feet of the building.
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. In
order to reveal the nature and extent of variations in the subsurface conditions below the
Job No. 114 189A
GLZtech
Desmond Home Builders
December 19, 2014
Page 3
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 concerned about MOBC,
then a professional in this special field of practice should be consulted.
We should observe the foundation excavation for the northern portion of the building
when complete.
If you have any questions or need further assistance,please call our office.
Sincerely,
HEPWORTH—PAWLAK GEOTECHNICAL, INC.
Thomas J. Westhoff, CET
Reviewed by:
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Steven L. Pawlak, P.E. "
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Attachment: Figure 1, Swell-Corr ration Test Results
Job No. 114 189A.
Gtech