HomeMy WebLinkAboutObservation of ExcavationMarch 27. 2014
Dale Titus
0171 Fairway Lane
Glenwood Springs. Colorado 81601
(dtitus01:1;
Job No. 114 0761
Subject: Observation of Excavation. Proposed Addition, Lot 30, Filing 2, Westbanfk
Subdivision, 0171 Fairway Lane, Garfield County, Colorado
Gentlemen:
As requested, a representative of Hepworth-Pawlak Geotechnical. Inc. observed the
excavation at the subject site on March 24, 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 performed in
accordance with our agreement for professional engineering services to you, dated March
18, 2014.
The addition will be attached to the backside of the existing residence and attached
garage. Spread footings placed on the natural soils and sized for an allowable bearing
pressure of 1500 psf were assumed for the building addition support. The addition will be
single story above crawlspace.
At the time of our visit to the site, the building addition excavation had been cut in one
level about 3%2 feet below the adjacent ground surface. The soils exposed in the bottom
of the excavation consisted of very moist, medium stiff, sandy silty clay. The excavation
depth was about 1'/a feet below the footing of the existing residence and the garage wall
appeared to bear on the slab without a footing. Results of swell -consolidation testing
performed on a sample taken from the bottom of cut, shown on Figure 1, indicate the soils
are moderately compressible under conditions of loading and wetting. The results of an
unconfined compressive strength test performed on a sample from the excavation bottom
showed a medium stiff consistency. The test results are summarized in Table 1. No free
water was encountered in the excavation and the soils were very moist.
The soils exposed in the excavation have low bearing capacity and are compressible
under Ioading. Lightly loaded spread footings placed on the undisturbed natural soil and
designed for an allowable soil bearing pressure of 1,000 psf can be used for support of the
proposed addition with some differential settlement potential across the addition and with
respect to the existing building. Footings should be a minimum width of 20 inches for
continuous walls and 2 feet for columns. Loose disturbed soils in footing areas should be
removed and the bearing level extended down to the undisturbed natural soils. Exterior
footings should be provided with adequate soil cover above their bearing elevations for
Dale Titus
March 27, 2014
Page 2
frost protection. Continuous foundation walls should be reintm•ced top and bottom to
span local anomalies such as by assuming an unsupported length of at least 14 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
relatively cry soil as backfill. A perimeter foundation drain should not be needed
provided foundation wall backfill is well compacted with a positive surface slope 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.
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
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.
If you have any questions or need further assistance, please call our office.
Sincerely.
HEPWORTH — PAWLAK GEOT HNICAL, INC.
Steven L. Pawlak, P.F.
SLP/ljg
Attachments: Figure 1 — SI "` �c., ion Test Results
Table 1 — Summary of Laboratory Test Results
cc: Pattillo Associates Engineers — Michael Strumph, PE (michael@paengineers.com)
job No. 114 076A
Gtech
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Moisture Content = 26.5 percent
Dry Density = 87 pot
Sample of: Sandy Silty Clay
From: Bottom of Addition Excavation, North Side
No movement
upon
wetting
0.1 1.0
114076A I
APPLIED PRESSURE • ksf
10
100
SWELL-CONSOUDATION TEST RESULTS I Figure 1
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