HomeMy WebLinkAboutObservation of Backhoe Pits 07.31.2014l HEPWORTH-PAWLAK GEOTECHNICAL
July 31, 2014
Joe Hultquist
402 Munroe Street
Rifle, Colorado 81650
joe@young-services.com
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Hcpworch·P<\\Yl .1k Gcotcchnic.1l, Inc .
5020 County RoaJ 154
GlcnwooJ Springs, Colormlo 8160 I
Ph me: 970 ·945 ·79 88
El\: 970 -945 -8454
crn :ul hpgcnig hpgcotcch.cum
Job No. 114 282A
Subject: Observation of Backhoe Pits, Proposed Shop Building, Ridge Road near
County Road 245 (Buford Road), Garfield County, Colorado
Dear Joe:
As requested, a represe~tative of Hepworth-Pawlak: Geotechnical observed backhoe pits
at the subject site on July 24, 2014 that had been excavated 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 perfo;"Ded in
accordance with our agreement for professional engineering services to you, dated July
17, 2014. Evaluation of the hillside cut stability is beyond the scope of this study.
Site Conditions: The site is located on an abandoned well drilling pad at the edge of the
Grand Hogback past Ridge Road. The northerly sloping terrain has been graded
relatively flat by cutting into the hillside and filling some on the downhill side. Bedrock
apparently of the Wasatch Formation is exposed in the steep hillside cut to the south.
Proposed Construction: The shop will be a steel frame and metal building with a sl ab-
on-grade floor at an elevation slightly above the existing ground surface. We assume
relatively light to moderate foundation loading supported by paqs and connecting grade
beam system.
Subsoil Conditions: At the time of our site visit, two backhoe pits located in about the
middle (Pit 1) and near the cut face to the southeast (Pit 2) had been dug. The soils
exposed in the pits, below about 1 to 2 feet depth of medium dense, clayey gravel with
cobbles consisted of weathered and medium hard claystone/sandstone bedrock that
extended down to the pit depths of 7 feet. The bedrock was more predominantly
weathered claystone in Pit 1 and more predominantly weathered sandstone in Pit 2 . The
material was too fractured to obtain undisturbed samples for swell-consolidation testing.
Parker 303-84 1-7119 • ColoradoSprings 7 19-633-5562 • Sih-er[home 970-468-1989
. . ' .
Joe Hultquist
July31, 2014
Page2
Laboratory testing perfonned on a disturbed bulk sample of the weathered claystone
consisted of natural moisture content, percent finer than sand size gradation analyses and
Atterberg limits with the results provided in Table I. No free water was encountered in
the pits and the soils and bedrock materials were slightly moist.
Recommendations: Spread footings bearing on the bedrock materials should be feasible
for foundation support of the building with some risk of movement. Based on our
experience with the Wasatch Fonnation and the medium plasticity of the weathered
claystone sample tested, the bedrock may possess a swell potential and the footings
should be designed for a minimum dead load pressure. The footings should be designed
for a maximum soil bearing pressure of 3,000 psf and a minimum dead load pressure of
800 psf. The expansion potential should be further evaluated at the time of construction.
The footings should be a minimwn width of 16 inches for continuous walls and 2 feet for
columns. All fill soil and loose disturbed materials in footing areas should be removed
and the bearing level extended down to the undisturbed bedrock and the subgrade
moistened and compacted. Exterior footings should be provided with adequate soil cover
above their bearing elevations for frost protection. Continuous foundation walls should
be reinforced top and bottom to span local anomaties such as by assuming an unsupported
length of at least 10 feet. A perimeter foundation drain should not be needed due to the
floor slab-at-grade construction. A minimum 2 feet of imported granular structural fill
such as road base should be provided below the floor slab due to the potentially expansive
subgrade conditions. Structural fill placed within floor slab areas should be compacted to
at least 95% of standard Proctor density at a moisture content at to slightly above
optimum. Backfill placed around the structure should be compacted to at least 90% SPD
(95% in pavement areas) and the surface graded to prevent ponding within at least 10 feet
of the building. Landscape that requires regular heavy irrigation, such as sod, and
sprinkler heads should not be located within 10 feet of the foundation.
Limitations: The recommendations submitted in this letter are based on our observation
of the soils exposed within the pit excavations and do not include subsurface exploration
to evaluate the subsurface conditions with depth. This study is based on the assumption
that soils and bedr~ck beneath the footings and at other areas of the site have equal or
better support than those exposed in the pits. The risk of foundation movement may be
greater than indicated in this report because of possible variations in the subsurface
conditions. We should observe the building excavation prior to footing construction to
evaluate the exposed materials for foundation support.
Job No. 114 282A
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Joe Hultquist
July31, 2014
Page 3
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.
DAY/ksw
attachment Table 1, Summary of Laboratory Test Results
cc: Albright and Associates -Jack Albright (jack@albri ght-associates.com)
Job No. 114 282A
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 1 Job No.114 282A
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION NATURAL NATURAL GRADATION ATTERBERG LIMITS
PERCENT AASHTO MOISTURE DRY GRAVEL SAND PASSING LIQUID PLASTIC CLASSIFICATION SOIL OR PIT DEPTH CONTENT DENSITY NO. 200 LIMIT INDEX BEDROCK TYPE ('Vo) ("/o)
SIEVE
(ft) (%} (Pct} (%) {%)
1 5-6 4 .5 75 30 16 Weathered Claystone
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