HomeMy WebLinkAboutObservation of Excavation 10.01.2021IC+A& ASSWates, hw. -Kmw
Geotechnigl and Materials Engineers 5020 County Road 154
and Environmental Scientists Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employ" OwmW Company www.kumarusa.com
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October 1, 2021
Ashley Bean
335 Elk Range Road
Garfield County, Colorado 81623
ashleben&gmail.com
Project No. 21-7-308
Subject: Observation of Excavations, Proposed Detached Garage and Residence Addition,
Lot 40, Panorama Ranch, 335 Elk Range Road, Garfield County, Colorado
Dear: Ashley:
As requested, a representative of Kumar & Associates observed the excavations at the subject
site on September 20 and 24, 2021 to evaluate the soils exposed for foundation support. The
findings of our observations and recommendations for the foundation support are presented in
this report. The services were performed in general accordance with our agreement for
professional engineering services to you dated March 29, 2021.
The garage will be built next to the carport and the addition will be attached to the southwest
corner of the residence. Both structures are proposed to be supported by spread footings placed
on the natural soils.
At the time of our initial visit to the site, the foundation excavation for the garage was mostly
complete and the residence addition excavation had not been started. When observed on
September 24, both excavations had each been cut in one level from about 2%2 to 4 feet below the
adjacent ground surface. The soils exposed in the bottom of the footing trench excavations
consisted of calcareous silty sand with basalt gavel and scattered cobbles and boulders. Clay soil
was exposed in the slab area of the garage. Results of swell -consolidation testing performed on a
sample of the clay, shown on Figure 1, indicate low to moderate compressibility under
conditions of loading and wetting. The results of a gradation analysis performed on a sample of
the calcareous silty sand and gravel (minus 1 %-inch fraction) obtained from the site are
presented on Figure 2. The laboratory test results are summarized in Table 1. No free water was
encountered in the excavation and the soils were slightly moist.
Considering the conditions exposed in the excavations 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 should be adequate for support of the proposed additions. The
exposed clay and silty sand matrix soils tend to compress when wetted and there could be some
post -construction settlement of the foundation if the bearing soils become wet. 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 moistened and compacted or removed and the bearing level
Ashley Bean
October 1, 2021
Page 2
extended down to the undisturbed natural 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 12 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 backfill excluding rock larger than about 4 inches. A perimeter
foundation drain does not appear needed provided backfill is well compacted with a positive
slope away from the foundation. Structural fill placed within floor slab areas can consist of the
on -site silty sand soils or imported road base 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 10 feet of the foundation.
The recommendations submitted in this letter are based on our observation of the soils exposed
within the foundation excavations 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,
Steven L. Pawla
SLP/kac
Attachments: F
;sults
Figure 2 — Gradation Test Results
Table 1 — Summary of Laboratory Test Results
Kumar & Associates, Inc. � Project No. 21-7-308
SAMPLE OF: Sandy Clay
FROM: Garage Slab
WC = 7 %, DD = 104 Pcf
—200 = 76 %, ILL = 38, PI = 17
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These teat results apply only to the
j samples tested. The testing report
shall not be reproduced, except in
full, without the written approval of
`i Kumar and Associates, Inc. Swell
Consolidation testing performed in
accordance with ASTM D-4546.
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21-7-308 Kumar & Associates SWELL —CONSOLIDATION TEST RESULTS Fig. 1
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HYDROMETER ANALYSIS
SIEVE ANALYSIS
TIME READINGS
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SILT AND CLAY 29 %
LIQUID LIMIT —
PLASTICITY
INDEX —
SAMPLE OF: Calcareous Silty Sand with
Basalt Gravel
FROM: Garage
Footing Trench
These test 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.
21
— —7-308
Kumar & Associates
GRADATION TEST RESULTS
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