HomeMy WebLinkAboutObservation of Excavation 11.08.2019li+A
Kumar & Assoclatzta, 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
November 8, 2019
Jacob Sampson
c/o Alii Construction
Attn: Felipe Sales
8000 County Road 313
New Castle, Colorado 81647
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Project No. 19-7-672
Subject: Observation of Excavation, Proposed Garage/Shop Attached to Existing
Residence, 1159 County Road 259, Garfield County, Colorado
Gentlemen:
As requested, a representative of Kumar & Associates, Inc. observed the excavation at the
subject site on November 7, 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 Jacob Sampson, dated November 6, 2019. H-P Geotech (now Kumar &
Associates) previously observed the excavation for the existing residence as described in a letter
dated June 21, 2016, Job No. 116 253A.
The proposed shop will be 30' by 30' in plan size, one story with a slab -on -grade floor. The
garage will be attached to the east side of the existing house. The foundation will consist of
18-inch wide continuous concrete footings with CMU block foundation walls.
At the time of our visit to the site, the foundation excavation had been cut in one level from 2 to
3 feet below the adjacent ground surface. The soils exposed in the bottom of the excavation
consisted of medium dense, silty sand. Results of swell -consolidation testing performed on a
sample taken from the site, shown on Figure 1, indicate the soils have low compressibility under
light loading and a low collapse potential (settlement under constant load) when wetted. The
soils were moderately to highly compressible under increased loading after wetting. No free
water was encountered in the excavation and the soils were slightly 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 garage with a risk of
settlement if the bearing soils become wet. The exposed soils tend to compress when wetted and
there could be differential post -construction settlement of the foundation if the bearing soils
become wet. Footings should be a minimum width of 18 inches for continuous walls and 2 feet
Jacob Sampson
November 8, 2019
Page 2
for columns. Loose and disturbed soils and any existing fill in footing areas should be removed
and the exposed bearing soils moistened and compacted. 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 heavily reinforced top and bottom to span local anomalies such as by
assuming an unsupported length of at least 14 feet. Structural fill placed within floor slab areas
can consist of 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 well -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. Consideration should be given to the use of xeriscape near the garage.
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.
F
Daniel E. Hardin, P.E. ;c 24443 2:
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attachment Figure 1— Swei onsolidation Test Results
Rev. by: SLP
DEH/kac
Kumar & Associates, Inc.',
Project No. 19-7-672
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SAMPLE OF: Silty Sand
FROM: Footing Grade at Southeast
Corner of Garage
WC = 5.5 %, DD = 92 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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1,0 APPLIED PRESSURE - KSF 10 100
19-7-672
Kumar & Associates I SWELL —CONSOLIDATION TEST RESULTS
Fig. 1