HomeMy WebLinkAboutObservation of Excavation.pdfil ./~tech HEPWORTH · PAWLAK GEOTECHNICAL June 12,2012 Marc Gube 232 Aspen Road Rifle, Colorado 81650 Cmarc@valcob.com) Ilqm'luh-I\l\\bk ('i~" ,1("'1. bnK,!!. 1111.. jO~t.) CIIIIIllV
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SUbject: Observation of Excavation, Proposed Addition to Garage, 232 Aspen Road, East of Rifle, Garfield County, Colorado Dear Marc: As requested, a representative of Hepworth-Pawlak
Geotechnical, Inc. observed the excavation at the subject site on June 7, 2012 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 June 7, 2012.
The addition will be attached to the north side of the garage and be a tall single story of wood frame construction with a slab-on-grade floor. The addition has been designed to be supported
on isolated spread footing pads assuming an allowable soil bearing pressure of2,000 pst: At the time of our site visit, the foundation excavation for the 6 footing pads to support the
addition had been each cut in one level about 3 feet below the adjacent ground surface. The soils exposed in the bottom ofthe excavation consisted of relatively dense, silty sandy gravel
and cobbles. The results of a gradation analysis performed on a sample of the coarse granular soils (minus 5 inch fraction) obtained from the site are presented on foigure I. No fi·ee
waLel was t:llcuuuLt:It:d iu Lht: t:xcavaLiun and the soils were slightly moist. Considering the conditions exposed in the excavations and the nature of the proposed construction, spread
footing pads placed on the undisturbed natural coarse granular soils designed for an allowable bearing pressure of2,000 psf can be used for support of the proposed addition. There could
be some differential settlement with respect to the existing structure which should be considered in the design. The footing pads should be a minimum width of2 feet. Loose and disturbed
soils in footing areas should be removed and the bearing level extended down to the undisturbed natural soils coarse granular. The footing pads should be provided with adequate soil
cover above their bearing elevations fur frost protection. We recommend 36 inches offrost cover be used for this area of Garfield County. Structural fill placed within floor slab areas
can consist of the on-site sand and gravel soils compacted to at least 95% of standard Proctor density at a moisture Parker 303·841·7119 • C.,lm"d" Sl'nn~' 719·6 "·5562 • :'ih errhllrne
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J ;\ .-I MarcGube June 12, 2012 Page 2 content near optimum. Backfill placed around the structure should be compacted and the surmce graded to prevent ponding within at least 10 feet
ofthe building. The recommendations submitted in this letter are based on our observation of the soils exposed within the foundation excavations and do not include subsurfuce exploration
to evaluate the subsurface conditions within the loaded depth offoundation influence. This study is based on the assumption that soils beneath the footings have equal or better support
than those exposed. The risk of fuundation 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 subsurfuce 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>-__ _ David A. Young, P.E. DAY/ljg attachment Figure I, Gradation Test Results cc: Garfield County Building Dept. -Jim Wilson (jwilsonUilgarfield-county.com)
Job No. 112 185A
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67 % Sand 24 % Silt and Clay 9 % Sample 01: Silty Sandy Gravel with Cobbles From: Bottom 01 Footing Pad Excavation 112185A ~ectl GRADATION TEST RESULTS FIGURE 1 HEPYlOATH-PAWlAK GEOTECHNICAL