HomeMy WebLinkAboutB15-0097_B15-0097 Open hole report_1431557880.pdf g".
1 Hep�•orrh-Pawlak Geotechnical, Inc.
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Phony:970-94i-79S8
HEPWORTH-PAWLAK GEOTECHNICAL F,ix:970-945-8454
email:hp;;eo@+hpgeutech.com
May 13, 2015
Evans Chaffee Construction
Attn: Chris Evans
P. O. Box 8266
Avon, Colorado 81620
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Job No. 115 206A
Subject: Observation of Excavation, Proposed Garage and Rear Entry
Additions, Evans Residence, Lot 16, Bighorn Subdivision, 4126a
Columbine Drive, Vail, Colorado
Dear Chris:
As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the
excavation at the subject site on May 11 and 12, 2015 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 in
general accordance with our agreement for professional engineering services to Evans
Chaffee Construction, dated May 7, 2015.
The additions will be single story wood frame construction with slab-on-grade floors.
The additions have been designed to be supported on spread footings assuming an
allowable soil bearing pressure of 3,000 psf. We understand the existing residence is
founded on spread footings.
On May 11, the excavation was underway with coarse granular soils being
encountered at the entryway area. At the time of our May 12 site visit, the foundation
excavations which were essentially complete had each been cut at one level from
about 2 to 4'A feet below the adjacent ground surface. The soils exposed in the
bottom of the excavations consisted of relatively dense, silty sandy gravel with
cobbles. No free water was encountered in the excavations and the soils were moist
to occasionally very moist apparently due to the recent snowmelt and run-off.
Considering the conditions exposed in the excavations and the nature of the proposed
construction, spread footings placed on the undisturbed natural granular soils
designed for an allowable bearing pressure of 3,000 psf can be used for support of the
proposed additions. There could be some differential settlement with respect to the
existing building which should be considered in the design. Footings should be a
minimum width of 16 inches for continuous walls and 2 feet for columns. Loose and
disturbed soils footing areas should be removed and the bearing level extended down
Parker 303-841-7119 • Colorado Springs 719-633-5562 • Silverthorne 970-468-1989
Evans Chaffee Construction
May 13, 2015
Page 2
to the undisturbed natural soils, and the subgrade compacted. 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 10 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 50 pcf for on-
site granular soil as backfill. Structural fill placed within floor slab areas can consist
of the on-sites and gravel soils compacted to at least 95% of standard Proctor density
(SPD) at a moisture content near optimum. 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.
While on site May 12, we observed dowel holes for two No. 5 reinforcement bars to
tie the new footings to existing footings. The dowel holes were 6 inches deep, % inch
diameter and observed to be clean prior to placement of the 31/2 feet long bars. The
bars were set in with Sure Anchor J51 epoxy. The dowels appear adequate and
similar to tie-ins for the foundation walls design.
The recommendations submitted in this letter are based on our observation of the soils
exposed within the foundation excavations 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 excavations, 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.
If you have any questions or need further assistance, please call our office.
Sincerely,
HEPWORTH—PA . AK GEOTECHNICAL, INC.
0011 I 11.6
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David A. Young, P.EZ Q
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Job No. 115 206A °tr�t"HM114410
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