HomeMy WebLinkAboutObservation of Excavation 10.23.2019Kumar & Associates, Inc.
Geotechnical and Materials Engineers
and Environmental 5cientisIs
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employee Owned Company www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
October 23, 2019
Kuersten Construction
Attn: John Kuersten
P.O. Box 1530
Rifle, Colorado 81650
joliuerstenconstruction.com
Project No. 19-7-603
Subject: Observation of Excavation, New Modular Building and Scales, Garfield County
Landfill, Anvil Points Road, County Road 256, West of Rifle, Garfield County,
Colorado
Dear John:
As requested, a representative of Kumar & Associates, Inc. observed the excavation at the
subject site on October 15, 2019 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 Kuersten Construction, dated October 9, 2019.
The proposed modular building will be a one story wood frame structure. The scales and
building will be supported on footings designed for an assumed allowable soil bearing pressure
of 3,000 psf.
At the time of our visit to the site, the foundation excavations had been cut in one level 31/2 feet
below the adjacent ground surface. The soils exposed in the bottom of the excavations consisted
of relatively dense, silty sandy gravel with cobbles (matrix supported, alluvial fan soils). The
subgrade had been compacted. The results of a gradation analysis performed on a sample of silty
sandy gravel with cobbles (minus 5 -inch fraction) obtained from the site are presented on
Figure 1. No free water was encountered in the excavations and the soils were slightly moist to
moist.
Considering the conditions exposed in the excavation and the nature of the proposed
construction, spread footings placed on the undisturbed natural soil designed for an allowable
soil bearing pressure of 3,000 psf can be used for support of the proposed modular building and
scales with a risk of settlement mainly if the bearing soils are wetted. Footings should be a
minimum width of 16 inches for continuous walls and 2 feet for columns. Loose disturbed soils
in footing areas should be compacted or removed and the bearing level extended down to the
Kuersten Construction
October 23, 2019
Page 2
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 45 pcf for on-site
gravel soil as backfill. A perimeter foundation drain should be provided to prevent temporary
buildup of hydrostatic pressure behind the crawlspace walls and prevent wetting of the lower
level. Structural fill placed within floor slab areas can consist of the on-site soils excluding rock
larger than 6 inches 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.
The recommendations submitted in this letter are based on our observation of the soils exposed
within the foundation excavation 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. In order to reveal the nature and extent of variations in
the subsurface conditions below the excavation, 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,
Kumar & Associates, Inc.
Daniel E. Hardin, P. .
Rev. by: SLP ,
DEH/kac
Q f-.
Attachment Figure 1 `' 'ratia'tion_T st Results
Kumar & Associates, Inc.
Project No. 19-7-603
HYDROMETER ANALYSIS
SIEVE ANALYSIS
TIME REAOINOS
29 HRS 7 NRS
100 s•r. MIN 15 MIN GOYIM 1914IM. 48111 1M11 !RM Tow /SO /1C R30 0 6 it?.
U.S. STANDARD SER/ES
90
60
70
60
50
40
30
20
10
0
.Ca I 002
I I Wizl r
oil
CLEAR Sa5AR£ OPENING!.
3/6' 3/4" i t/2' 3'
4 t. _ I 1.471s1
.160 .500 1 I I .1.600 I IIIr. I I .1 11111
1 R 2 0.36 4.76 6
DIAMETER OF PARTICLES IN MILLIMETERS
19
10
20
30
40
50
60
70
80
90
I I !_II.11 100
35.1 76.2 137 202
162
1
CLAY TO SILT
GRAVEL 60 X
LIQUID LIMIT
SAND
GRAVEL
FINE
SAND 22 X
I MEDIUM
COARSE
FINE
COARSE
COBBLES
PLASTICITY INDEX
SILT AND CLAY 18 X
SAMPLE OF: Silty Sandy Gravel with Cobbles FROM: Footing Grade
These teal results apply only to the
samples which were Tested. The
feellnp. roporl shall noI be reproduced,
esoept In full, wlthoul the pen
approval 01 Kutner & Assoaiolss, Ina.
Slays analysts lnl1ny is performed In
eecard0nee wlh ASTM 06913. ASTM D7928,
ASTM C136 and/or ASTM D1140.
19-7-603
Kumar & Associates
GRADATION TEST RESULTS
Fig. 1