HomeMy WebLinkAboutObservation of Excavation 10.30.15~ec
HEPWORTH-PAWLAK GEOTECHNICAL
October 30, 2015
Lisbeth Oden
P.O. Box 1677
Glenwood Springs, Colorado 81602
( cabindream@me.com )
l lcp11vrth·P.1wl.1k Gco1cclm1L.1l, Inc
5010 Count~· Ro.id 15-t
GlcnwooJ Sprin~'S, Cnlor.1do 81601
l'bon.: 970-9·U· 7933
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Job No. 115 130A
Subject: Observation of Excavation. Proposed Cabin, Lot 4, Sillivan Subdivision,
4726 County Road 335, Garfield County, Colorado
Dear Beth:
As requested by Mark Miller, a representative of Hepworth-Pawlak Geotechnical
observed the excavation at the subject site on October 17, 2015 to evaluate the soils
exposed for foundation support. The findings of our observations and recommendations
for the foundation design arc 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
May 29, 2015, Job No. 115 130A.
The proposed construction is similar to that discussed in our previous report. The
building has been designed to be supported on spread footings using an allowable soil
bearing pressure of 1 ,000 psf as recommended with some risk of settlement.
At the time of our site visit, the foundation excavation which was essentially complete
had been cut in several levels from about 2 to 9 feet below the adjacent ground surface.
The soils exposed in the bottom of the excavation consisted primarily of medium dense,
silty occasionally clayey sand and gravel with cobbles (to about 8 inches in diameter).
There were several scattered pockets of medium dense, silty to clayey sand with scattered
gravel. Results of swell-consolidation testing perfonned on a sample of the clayey sand
taken from the site from one of the pockets. shown on Figure J, indicate the soils are
moderately compressible under conditions of loading and welling with a minor swell
potential when wetted under a constant 500 psf surcharge. No free water was
encountered in the excavation and the soils were slightly moist to moist. The excavation
subgrade was not compacted and at this time we recommended the footing subgrade areas
be compacted which was done.
The soil conditions exposed in the excavation are consistent with those previously
encountered on the site and suitable for support of spread footings designed for the
recommended allowable bearing pressure of I ,000 psf. The risk of foundation settlement
appears low. however, excessive wetting of the bearing soils may cause some settlement
and precautions should be taken to prevent wetting. Structural filJ below the footings
Parker 303-841-7119 • Color.ido Springs 719-633-5562 • Stlvcrrhome 970-468-1939
Lisbeth Oden
October 30, 2015
Page 2
docs not appear needed. The minor swell potential measured in the one sample can be
neglected in the foundation and floor slab design. Prior to the footing construction, loose
disturbed soils should be removed to expose the undisturbed natural soils and the
subgrade re-compacted as needed. Other recommendations presented in our previous
report which are applicable should also be observed.
The recommendations submitted in this letter are based on our observation of the soils
exposed within the foundation excavation and the previous (limited) subsurface
exploration at the site. Variations in the subsurface conditions below the excavation
could increase the risk of foundation movement. We should be advised of any variations
encountered in the excavation conditions for possible changes to recommendations
contained in this letter.
If you have any questions or need further assistance, please call our office.
Sincerely,
cc: Pattillo Associates Engineers -Bob Pattillo (bob@ paen ginecr!i.com >
Three G Construction-Mark Miller (t.~rcc g co niruuc ti on @msn.com )
Garfield County Building Dept. -Jim Wilson (jwil!,on@ garfield-count y.com}
Job No. 115 l30A
Moisture Content = 9.1 percent
Dry Density • 89 pcf
Sample of : Clayey Sand with Gravel
From: Bottom of Northwestern Portion of
Excavation
1
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0 0 c;; c: • ll... t'O ---r-..
Q. ...... >11 ""' 1-.h in I\ t • 1 I\ \ .§ ~ f.,."
rn
~ 2 \ \ a. g
u \ \ 3 Expansion \ upon
wetting
4
' 5 l'I
0.1 10 10 100
APPLIED PRESSURE -ksl
115 130A cGetech SWELL-CONSOLIDATION TEST RESULTS Figure 1
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