HomeMy WebLinkAboutObservation of Excavation 03.27.2015HEPWORTH-PAWLAK GEOTECHNICAL
March 27, 2015
Phil & Lisa Ensign
1 South Garfield Street
Denver, Colorado 80209
Job No, 114542R
Subject: Observation of Excavation, Proposed Residence, Lot 23, High Aspen
Ranch, Overlook Drive, Garfield County, Colorado
Dear Mr. & Mrs. Ensign:
As requested, a representative of Hepworth-Pawlak Geottehnieal, Inc. observed the
driveway subgade and excavation in the building area at the subject site on February
3, 2015 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 February 4, 2015.
At the time of our visit to the site, the driveway had been rough graded and the
building area had been ;pass excavated and cut in one level up to 8 feet below the
adjacent ground surface. The soils exposed at the driveway cut grade and bottom of
the excavation in the building area consisted of basalt rocks from gravel to boulder
size in a sandy silty clay matrix. The results of a gradation analysis performed on a
sample of basalt gravel and cobbles in sandy clay matrix (minus 5 inch fraction)
obtained from the site are presented on Figure 1. The soils have a USDA
Classification of very gravelly sandy loam. No free water was encountered in the
excavation and the soils were moist.
Residence: Considering the conditions exposed in the building area excavation and
the nature of the proposed construction, spread footings placed on the undisturbed
natural soil designed for an allowable soil bearing pressure of 2,000 psf can be used
for support of the proposed residence. Footings should be a minimum width of 16
inches for continuous walls and 2 feet for columns. Loose and disturbed soils in
footing areas should be compacted or removed and the bearing level extended down
to the undisturbed natural soils. The bearing soils should be protected against frost
and concrete should not be placed on frozen soils. Exterior footings should be
provided with adequate soil cover above their bearing elevations 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 10 feet. Foundation
walls acting as retaining structures should also be designed to resist a lateral earth
pressure based on an equivalent fluid unit weight of at least 50 pcf for on-site soil as
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Phil & Lisa Ensign
March 27, 2015
Page 2
backfill excluding rock larger than about 6 inches. A perimeter foundation drain
should be provided to prevent temporary buildup of hydrostatic pressure behind the
crawlspace and basement walls and prevent wetting of the lower level. Structural fill
placed within floor slab areas can consist ot'the on-site soils compacted to at least
95% of standard Proctor density at a moisture content near optimum. Backfill placed
around the structure should be compacted and the surface graded to prevent ponding
within at least 10 feet of the building.
Driveway Subgrade: The driveway subgrade appears stable. Low areas and holes
created by boulder removal should be backfilled with compacted structural till
consisting of the on-site soils or a suitable imported granular material minus topsoil,
organics and over -sized rock. The structural fill should be compacted to at least 95%
ofthe-maximum standard Proctor density at a moisture content near optimum.
The recommendations submitted in this letter are based on our observation of the soils
exposed within the building area excavation and exposed driveway subgrade and do
not include subsurface exploration to evaluate the subsurface conditions within the
loaded depth of foundation influence. This study is based on the assumption that soils
beneath the footings have equal or better support than those exposed. The risk of
foundation movement may be greater than indicated in this report because of possible
variations in the subsurface conditions. 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 -- PAWLAK GEOTECHNICAL, INC.
G
Daniel l.. 1 iarclin. €', f
Rev. by: S LP
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attachment Figure I — USDA Gradation Test Results
cc: Thunder Construction — Monty Thomson (ph tIpnlef t �-�
High Country Engineering- Matt Langhorst (Nblf _r,:11)
Job No 114 5421
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DIAMETER PAR 1 3Sw WitgCE
GRAVEL 51 % SAND 11 %
USDA SOC TYPE: Vey Gravelly Sandy am am
SILT 21 % CLAY 17 %
2
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FROM, Lot 23, High Aspen Ranon
H-PKUMAR
TABLE 2
PERCOLATION TEST RESULTS
PROJECT NO. 17-7-561
Page 2 of 2
HOLE NO.
HOLE
DEPTH
(INCHES)
LENGTH OF
INTERVAL
(MIN)
WATER
DEPTH AT
START OF
INTERVAL
(INCHES)
WATER
DEPTH AT
END OF
INTERVAL
(INCHES)
DROP IN
WATER
LEVEL
(INCHES)
AVERA
PERCOU
RAT
(MIN./IN
P4
38
15
5
41/4
3/4
60/1
4%
41/4
1/2
41/4
3%
'/2
41/2
41/4
1/4
41/4
4
1/4
P5
25
15
4
31/2
1/2
30/1
41/4
31/2
3/4
4
___. .... --........
4
31/2
1/2
31/2
1/2
31/2
3
1/2
P 6
24
15
6
53/4
1/4
120
53/4
51/2
1/4
51/2
51/4
1/4
51/4
51/2
1/8
51/
5
1/
GE 1
TION :
CH)
1
Note: Percolation test holes were hand dug in the bottom of backhoe pits and soaked
on August 2, 2017. Percolation tests were conducted on August 3, 2017. The
average percolation rates were based on the last two readings of each test.