HomeMy WebLinkAboutObservation of Excavationl$ltiffil*iffiffir'ffd'*-"502û Clounty Road I J4
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Office l-ocatio¡u: Ðcnver {I'lQ), Parker, Colorarlo Springs, Iìort Collins, Cle*woocl Springs, and Sunmit t--ounty, Colorado
Septernber 29,2021
Barbara Keranen
699 Bristlecone Way
Silt, Colorado 81652
klanen barbalAf¿ùhotmail. coru
Project No.21-7-574
Subject: Observation of Backhoe Pit Excavation, Tract 8 Scutter Lane, Graham Mesa,
Garfield County, Colorado
Dear Ms. Keranen:
As requested, a representative of Kumar & Associates, Inc. observed the backhoe pit excavation
at the subject site on September 24,2021 to evaluate the bedrock for foundation support. The
findings of our observations and recommendations for the foundation design are presented in this
report. We previously conducted a subsoil study for design of foundations at the site and
presented our findings in a report dated August 26,2021, Project No. 21-7-574.
Our previous subsurface exploration at the site encountered sandstonelsiltstone bedrock at a
depth of around 7 feet at Boring 2 ínthe proposed garage area. The sandstone/siltstone bedrock
âppears suitable for support of spread footings with low movement risk. The clay and claystone
encountered in Boring 1 and above the sandstone/siltstone layer are expansive and not suitable
for support of spread footings due to excessive movement risk.
At the time of our site visit, a pit was excavated with a backhoe near the center of the proposed
residence. Below the clay soils, sandstone/siltstone bedrock was encountered at a depth of
7% feet to the pit depth of 8 feet that was too hard to sample for expansion testing. Based on the
subsurface profile, the sarrdstone/siltstone bedrock or compacted structural fill placed after sub-
excavating the clay and claystono can be used for support of spread footings sized for an
allowable bearing pressure of 2,000 psf. Footings should be a rninimum width of 16 inehes for
walls and 2 feet for columns. The structural fill should consist of a relatively well gracled
granular material, such as CDOT Class 6 base course, oompacted to at least 98% of standard
Proctor density at near optimum moisture content. The structural fill should extend laterally
beyond the footing edges a distance equal to at least one-half the depth of fill below the footing.
We should observe the completed excavation down to sandstone/siltstone prior to fbrming
footings or placing structural fill, Other recommendations presented in our previous report
which are applicable should also be observed.
Barbara Keranen
September 29,2021
Page2
If you have any questions or need further assistance, please call our office.
Sincerely,
Kumar & Associates, Inc.
Steven L. Pawlak, P.E.
SLP/kac
Kumar & Associates, lnc. o Project No.21-7-574