HomeMy WebLinkAboutObservation of Pits for Foundation Design 10.09.2019Kumar & Associates, Inc."
Geotechnical and Materiels 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
October 9, 2019
Bill Rice
P. O. Box 1252
Carbondale, Colorado 81623
b i l l ri ce(F4sopris. tiet
Subject:
Bill:
Project No. 19-7-526
Observation of Pits for Foundation Design, Proposed Lean -To Building,
544 County Road 100, Garfield County, Colorado
As requested, a representative of Kumar & Associates, Inc. observed two pits in the area of the
proposed building at the subject site on October 4, 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 you, dated September 5, 2019.
Proposed Construction: The proposed lean-to building will be a 32 foot by 210 foot single -
story wood frame structure with 4 units and pad and grade -beam foundation. Ground floor will
be slab -on -grade. Cut depths are expected to range between about 1 to 2 feet. Foundation
loadings for this type of construction are assumed to be relatively light and typical of the
proposed type of, construction.
If building conditions or foundation loadings are significantly different from those described
above, we should be notified to re-evaluate the recommendations presented in this report.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits in the proposed building area. The subsoils encountered, below about 1 to 2 feet
of fill, consist of silty sandy gravel with cobbles and small boulders down to the maximum depth
explored of 7 feet. Results of a gradation analysis performed on a sample of silty sandy gravel
(minus 8 -inch fraction) obtained from Pit 2 at a depth of 3 to 4 feet are presented on Figure 1.
No free water was observed in the pits at the time of excavation and the soils were slightly moist
to moist.
Findings and Recommendations: Considering the conditions exposed in the pits and the nature
of the proposed construction, spread footings placed on the undisturbed natural gravel soil
designed for an allowable soil bearing pressure of 3,000 psf can be used for support of the
proposed building. Footings should be a minimum width of 16 inches for continuous walls and
Bill Rice
October 9, 2019
Page 2
2 feet for columns. Loose and disturbed soils and existing fill 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 to resist a lateral earth pressure
based on an equivalent fluid unit weight of at least 45 pcf for on-site soil as backfill. Structural
fill placed within floor slab areas can consist of the on-site soils excluding rock larger than about
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. Landscape that requires regular heavy
irrigation, such as sod, and sprinkler heads should not be located within 5 feet of the foundation.
The recommendations submitted in this letter are based on our observation of the soils exposed
within the pit excavations near the building footprint. This study is based on the assumption that
soils throughout the building site 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,
Kumar & Associates, Inc.
Robert L. Duran
Reviewed by:
Steven L. Pawlak,
RLD/kac
attachment: Figure 1 — Paitic c Size Distribution Report
Kumar & Associates, Inc.
Project No. 19-7-526
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100 10 1 0 1
GRAIN SIZE - mm.
0.01 0.001
+3"
%Coarse
% Gravel
% Sand
% Fines
1 Fine
Coarse
Medium
T Fine
Silt I Clay
35
11
7
4
8
13
22
SIEVE PERCENT
SPEC.*
PASS?
Material Description
SIZE
FINER
PERCENT
(X=NO)
Silty Sandy Gravel with Cobbles
8
5
3
100
77
65
Atterberg Limits
1.5
3/4"
3/8"
58
54
50
PL= LL= PI=
Coefficients
#4
#8
#16
#30
47
44
41
37
D90= 165.6441 D85= 149.5554 D60= 46.4444
D50= 9.5250 D30= 0.2274 015=
010= Cu- Cc=
Classification
#50
#100
#200
32
27
22
USCS= AASFITO=
Remarks
r (no specification provided)
Location: Southwest Comer, Pit 2 @ 3'-4'
Sample Number: 424-19 Date: 10/4/2019
Kumar & Associates, Inc.
Glenwood Springs, Colorado
Client: Bill Rice
Project: 544 County Road 100, Garfield County, Colorado
Project No: 19-7-526 _ Figure 1 ,-
Tested
Tested By: KO
Checked By: SLP