HomeMy WebLinkAboutObservation of Excavation03/29/2013 11:00 19709458454 HPGEOTECH PAGE
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WEPWORTH-PAWLAK GEOTECHNICAL Fig; 670-941-1454
March 29, 2013 0111:411: ,,u�pr,rn, ,a •9itd,.c9m
Planted Earth
Attn: Steve Schubert
12744 Highway 82
Carbondale, Colorado 81623
Job No. 113 069A
Subject: Observation of Excavation, Proposed Greenhouse, Planted Earth, 12744
Highway 82, Garfield County, Colorado
Mr. Schubert:
As requested by Brad Larson, a representative of Hepwot�th-Pawlak Geotechnical, Inc.
observed the excavation at the subject site on March 27, 2013 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 Planted Earth,
dated March 27, 2013.
The greenhouse will be attached to an existing block building located in the middle north
part of the property. The slope is gentle across most of the building site then steep up
about 6 feet at the back, north side to a relatively flat graded arca. Continuous spread
footings and concrete stem walls have been designed to support the greenhouse. Covered
planters are proposed along the front side and the backside will retain about 4 feet of earth
backfill.
At the time of our visit to the site, the footing trench excavations had been cut in one level
from I'i to 6 feet below the adjacent ground surface. The middle, proposed slab -on -
grade area was cut flat about 1% feet above the footing trench excavation level. The soils
exposed in the bottom of the footing trench excavation consisted of silty to clayey sand
with gravel. ,results of swell -consolidation testing performed on samples taken from the
footing trench bottom, shown on Figure 1, indicate the soils ate slightly compressible
under light loading and natural low moisture conditions with low to moderate collapse
potential (settlement under constant loading) when wetted. No free water was
encountered in the excavation and the soils were slightly moist. Part of the excavation
bottom had been compacted and it was recommended to moisten and compact the entire
footing areas.
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 1,500 psf can be used for support of the proposed
greenhouse. The exposed soils tend to compress when wetted under load and there could.
be 1 to 2 inches of Post -construction foundation settlement (assuming about 5 feet of
compressible soil depth abovo dense river gravel) if the bearing soils become wet.
Footings should be a minimum width of 20 inches (24 inches at the backside) for
Parker 303-541-7119 + C;nl,:rrad, Springs 7196.33.5562 0 5i1vu-thoine 970-468,1989
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Planted Faith
March 29, 2013
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continuous walls and 2 feet for isolated columns. Loose disturbed soils in footing areas
should be moistened and compacted. The bearing soils should be protected against fiost
and concrete should not be placed on frozen soils, Exterior footings should be provided
with adequate soil cover above their bearing elevations or with rigid insulation for frost
Protection. Continuous foundation walls should be reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 12 feet. The uphill
foundation wall that acts as a retaining structure should also be designed to resist a lateral
earth pressure based on an equivalent fluid unit weight of at least 50 pef fot on-site soil as
backfill. A perimeter foundation drain should not be provided sinnce introducing water a
the bearing soils could cause foundation settlement. An impervious membrane, such as
20 mil PVC liner, should be provided oil the bottomoftine fn•ont planters to prevent
wetting of tile bearing soils. Structural fill placed within floor slab areas can consist of the
rnn-site soils compacted to at least 95% of standard Proctor density at a moisture content
near optimuln. Backfill placed around the structure should be compacted to at least 9o%
ofstaudard Proctor density and the surface graded at a minimum 5% to prevent ponding
within at least 5 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 ill 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 tine loaded depth of foundation influence. This
study is based on the assumption that soils beneath tine footings have equal or better
support than those exposed. The risk of founon movement may be greater than
dati
indicated in this report because o.fpossible 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 of other biological
contaminants (MOBC) developing in the future. If the client is concerned about .MOBC,
then a. professional in this special field of practice alnould be consulted.
If you have any questions or need further assistance, please call our office.
Sincerely,
HEPWORTH — PAWLAK_5jOTLWT1WCAL, INC.
Steven L. Pawlak, P.E,222
SLP/Ijg 318'111?
Attachment: Figure 1 — Swe COG
ation Test Results
cc: Brad Larson &adIqg@cOnLst.net
Job Nq Ir3069A .—..�