HomeMy WebLinkAboutObservation of Excavation 03.26.2020K+A
Kumar & Associates, Inc.
Geotechnical and Materials Engineers
and Environmental Scientists
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
March 26, 2020
Darren Gallegos
58 Surrey Street
Carbondale, Colorado 81623
darrengallegos@hotmail.com
Project No. 20-7-200
Subject: Observation of Excavation, Proposed Residence, Lot 11, Ranch Creek PUD,
Ranch at Roaring Fork, Surrey Street, Garfield County, Colorado
Dear Darren:
As requested, a representative of Kumar & Associates, Inc. observed the excavation at the
subject site on March 23, 2020 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 March 23, 2020.
The proposed residence will be a two-story wood frame structure with an attached garage. The
main floor and garage floor will be slab -on -grade. Footing foundations were designed for an
assumed allowable soil bearing pressure of 1,500 psf.
At the time of our visit to the site, the foundation excavation was about 90% complete and had
been cut in one level about 21/2 feet below the adjacent ground surface. The garage footing
trench had not been excavated and the small area south of the garage is planned to be excavated
down an additional 10 inches. The soils exposed in the bottom of the excavation consisted of
medium dense, slightly silty sandy gravel with cobbles and scattered small boulders. The results
of a gradation analysis performed on a sample of slightly silty sandy gravel (minus 3-inch
fraction) obtained from the site are presented on Figure 1. No free water was encountered in the
excavation 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 1,500 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 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 (if any) should also be designed
Darren Gallegos
March 26, 2020
Page 2
to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 45 pcf for on -
site soil as backfill. A perimeter foundation drain should not be needed for the proposed slab -on -
grade main floor. Structural fill placed within floor slab areas can consist of the on -site soils
(4-inch minus) 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. Hardii
Rev. by: SLP
DEH/lac
attachment Figure 1 — Gradation Test Results
cc: Studio M — Mic Baca studiom.engineer@gmail.com
Kumar & Associates, Inc.
Project No. 20-7-200
HYDROMETER ANALYSIS
SIEVE ANALYSIS
100
TIME READINGS
24 HRS 7 HRS
45 MIN 15 MIN 6014111 19MIN 4MIN WIN
U.S.
STANDARD
SERIES
0
1 •
CLEAR SQUARE OPENINGS
3 4' 8'6' -'0
I-
I
90
—
1
r
10
I
1
--
80
I
I
I
20
f
I
70
I
I
I
---------♦
I
I
30
I
so
T
— - -
1
t
50
I
}
I
60
1
ao
I
}
1
so
4
20
—--
—1
-
80
10
—
I
1
90
-I-
-
0
I I III
I._.= I
I LI1 I
L I 1 11
i
T 1 I I R11__
1-1-1.1 1 1 I I I
= 100
_—L __LI1 _I —I
.001 .002 .005 .009 .019 .037 .075 .150 .300 I .600 1.18 12.36 4.75 9 5 19 38.1 76.2 127
.425 2.0 152
DIAMETER OF PARTICLES IN MILLIMETERS
200
CLAY TO SILT
SA ND
GRAVEL
FINE MEDIUM COARSE
MEDIUM
FINE
COBBLES
GRAVEL 59 % SAND 31 % SILT AND CLAY 10 %
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Slightly Silty Sandy Gravel FROM: SE Corner of Excavation at Footing Grade
These fest results apply only to the
samples which were tested. The
testing report shall not be reproduced,
except in full, without the written
approval of Kumar & Associates, Inc.
Sieve analysis testing is performed in
accordance with ASTM D6913, ASTM D7928,
ASTM C136 and/or ASTM D1140.
20-7-200
Kumar & Associates
GRADATION TEST RESULTS
Fig. 1