HomeMy WebLinkAboutObservation of Excavation 10.31.14..
HEPWORTH-PAWLAK GEOTECHNICAL
October 31, 2014
Gray Builders
Attn: Dale Gray
P. 0. Box 362
New Castle, Colorado 81647
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Job No. I 14 172A
Subject: Observation of Excavation, Proposed Lodge Area Pool, Storm King
Ranch, 1541 County Road I 32, Garfield County, Colorado
Dear Dale:
As requested, the undersigned representative of Hepworth-Pawlak Geotechnical observed
the excavation at the subject site on October 28, 30 and 3 l , 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. We previously conducted a subsoil
study for design of foundations at the site and presented our findings in a report dated
June 30, 2014, Job No. I 14 l 72A .
The pool location has been moved to the north to the area of Borings l and 2 drilled for
our subsoil study. The proposed construction for the pool is similar to that discussed in
our report and consists of reinforced gunnite. The pool will be 8 feet deep in about the
western half sloping up to 3Yz feet deep at the east end. A spread footing foundation
bearing on the natural soils and/or compacted structural fill designed for an allowable soil
bearing pressure of 2,000 psf were recommended for foundation support.
On October 28, the excavation was about half complete (the western portion) with cut
depths of about l 0 feet below the adjacent ground surface and primarily clayey silty
sandy gravel with small cobbles exposed at subgrade. There were occasional pockets of
clay soils exposed within the gravel soils. While on site, we observed the soils exposed in
a backhoe excavated in the east-central end of the proposed pool. The soils in the pit
consisted of considerable fill and topsoil with clayey silty sand exposed in the bottom of
the pit at about 5Yz feet depth. Results of swell-consolidation testing perfonned on
samples taken from the site, shown on Figure I, indicate the sand soils are slightly
compressible and clay soils are moderately compressible under conditions ofloading and
wetting. No free water was encountered in the excavation and the soils were generally
moist. The clay soils were occasionally calcareous. At this time we recommended the
excavation be dug to design elevations and we observe the excavation subgrade
conditions.
Gray Builders
October 31, 2014
Page 2
On October 30, the excavation had been dug to design elevations ranging from about 5Yi
(east end) to 10 feet (west end) below the adjacent ground surface with clay soils exposed
in the east portion and topsoil overlying the clay in the southeast comer. At this time we
recommended the topsoil be removed. On October 31, the excavation was essentially
complete and had been cut from about 6Yi to 10 feet below the adjacent ground surface
with a slope down to the western half where the deep end bottom of the pool was
relatively flat. The eastern portion had been deepened up to about 30 inches below design
excavation grade to remove the topsoil and predominantly clay soils. The soils exposed
in the bottom of the excavation consisted of medium dense, clayey silty sandy gravel with
small cobbles in the western portion and medium dense, clayey silty sand in the eastern
portion. No free water was encountered in the excavation and the soils were generally
moist.
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 2,000 psf. Loose and disturbed soils should
be removed in the footing areas to expose the undisturbed natural soils and the subgrade
compacted. Road base consisting of~ inch aggregate base course compacted to at least
95% standard Proctor density should be used to re-establish design excavation subgrade.
The bearing soils should be protected from frost and concrete should not be placed on
frozen soils. Other recommendations presented in our previous report which are
applicable, including those relating to an underdrain below the pool, 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 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,
DAY/ksw
attachment
Job No. 114 172A
~tech
Moisture Content = 27.2 percent
0 Dry Density = 72 pcf
Sample of: Si lty Sandy Clay ---r-i-""() From: Pool Excavation , Bottom of North-Cen tral
1 ,_ ....._ Portion
~ \
2 -~ ~ * .._..
z 3
0 ') ...... Compression ........ en I ,.......
r-upon (/) \ i-_
w r---wetting a: 4 a. I
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0 \ (..)
5
' )
6
0.1 1.0 10 100
APPLIED PRESSURE ( ksf)
Moisture Content = 24 .0 percent
Dry Density = 97 pcf
Sample of: Clayey Silty Sand
From: Pit at East End of Poo l at 5 1/2 Feet Depth
0
-,__ --i-. i--(~ 1 -(_ ' ~ * ~' .._..
z 2
0 No 'O en
(/) movement w upon wettino a: 3 a.
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0
(..)
4
5
0.1 1.0 10 100
APPLIED PRESSURE ( ksf)
114 172A ~tech SWELL-CONSOLIDATION TEST RES UL TS FIGURE 1
HEPWORTH·PAWLAK GEOTECHNICAL